Pelagic Shrimps of the

Sergestes edwardsii Species Group

Crustacea: Decapoda: Sergestidae)

DAVID C. JUDKINS

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 256
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SMITHSONIA N CONTRIBUTION S T O ZOOLOG Y • NUMBE R 25 6

Pelagic Shrimps of the

Sergestes edwardsii Species Group

(Crustacea: Decapoda: Sergestidae)

David C. Judkins

SMITHSONIAN INSTITUTION PRESS

City of Washington

1978
ABSTRAC T

Judkins, David C. Pelagic Shrimps of the Sergestes edwardsii Species Group

(Crustacea: Decapoda: Sergestidae). Smithsonian Contributions to Zoology,

number 256, 34 pages, 21 figures, 4 tables, 1978.—This global study of the systematics and distribution of the edwardsii species group is based upon examination of several hundred micronekton samples collected at stations scattered

throughout the world ocean. Eight species, including three new ones, are recognized and described. Although the group is represented in all tropical and in

certain subtropical oceanic regions, individual species have geographically restricted ranges. Conventional and numerical phyletic analyses reveal at least two,

and perhaps three, closely related yet distinct lineages within the group. Species

distributions tend to be allopatric or parapatric, overlap being most extensive

between species of different lineages. Evidence of character divergence in reproductive structures of co-occurring species is discussed.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea

cavernosa Linnaeus).

Library of Congress Cataloging in Publication Data

Judkins, David C.

Pelagic shrimps of the Sergestes edwardsii species group (Crustacea: Decapoda: Sergestidae)

(Smithsonian contributions to zoology ; no. 256)

Bibliography; p.

1. Sergestes. 2. Crustacea-—Classification. 3. Crustacea—Geographical distribution. I. Title. II.

Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 256.

QL1.S54 no. 56 [QL444.M33] 591'.08s [595'.3843] 77-608177
Contents

Page

Introduction 1

Methods 1

Abbreviations 3

Acknowledgments 3

Genus Sergestes Milne-Edwards, 1830 3

Sergestes edwardsii Species Group 4

Key to Species of the edwardsii Group 7

1. Sergestes edwardsii Kroyer, 1855 8

2. Sergestes brevispinatus, new species 13

3. Sergestes consobrinns Milne, 1968 16

a. California Current Form 16

b. Central Form 18

4. Sergestes tantillus Burkenroad, 1940 19

5. Sergestes semissis Burkenroad, 1940 21

6. Sergestes orientalis Hansen, 1919 23

7. Sergestes geminus, new species 25

8. Sergestes gibbilobatus, new species 27

Phylogenetic Relationships 28

Comments on Distribution 31

Literature Cited 33

in

Pelagic Shrimps of the

Sergestes edwardsii Species Group

(Crustacea: Decapoda: Sergestidae)

David C. Judkins

Introduction

Systematic studies of pelagic marine taxa have

been hindered by the circumglobal extent of many

of these groups and the frequently slight degree of

difference distinguishing their species. Consequently, many pelagic groups are in need of revision on a global scale, a task only recently made

possible by the combined efforts of many oceanographic organizations. Recent revisions of oceanic

taxa based on comparisons of material collected

from throughout the world ocean invariably have

revealed undescribed species (e.g., Ebeling, 1962;

Frost and Fleminger, 1968; Bowman, 1973; Fleminger, 1973; Fleminger and Hulsemann, 1974;

Johnson, 1974). In addition to refining our taxonomic resolution of important marine groups, such

studies also have contributed greatly to our knowledge of their evolution and distribution. The

present work is a global study of the taxonomy,

distribution, and relationships of the Sergestes edwardsii species group, a monophyletic assemblage of

pelagic decapod shrimps.

The edwardsii group is one of six species groups

comprising the holopelagic penaeidean genus Sergestes. Species of the edwardsii group occur throughout tropical and certain subtropical regions of the

world ocean. They are frequent and often abundant components of micronekton collections made

David C. Judkins, Oceanographic Sciences Division, Brookhaven National Laboratory, Upton, New York 11973.

within their ranges. The present study was

prompted by the near absence of distributional

data on the group and the need for full taxonomic

treatment of species, previously described in only

preliminary fashion by Burkenroad (1940). Early

in the study, I discovered several undescribed populations, three of which are sufficiently divergent in

morphology and geographical habitat from other

members of the group to be recognized as separate

species. In this report, I describe all species and

morphologically divergent populations of the edwardsii group and delimit their geographical distributions. I also examine and discuss phylogenetic

relationships and biogeographic patterns within the

group.

METHODS.—The majority of specimens examined

in this study were taken with either the Isaacs-Kidd

midwater trawl (IKMT) or the Blackburn micronekton net (BMN). However, a substantial number

were collected with other gear, including the

Tucker trawl and conical nets of various mouth

diameters. Collections varied greatly in speed and

duration of haul and in season, time of day, and

depth interval sampled. A listing of station data

and data sources has been deposited in the National

Museum of Natural History (NMNH), Smithsonian Institution, Washington, D. C.

With few exceptions, collections were examined

in their entirety for adults of the closely related

genera Sergestes and Sergia (cf. Omori, 1974). Figure 1 depicts the geographical distribution of collections containing specimens of those genera.
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 1.—Distribution of collections yielding specimens of the genera Sergestes and Sergia

(more than one collection may be represented by a single open circle at localities where stations

overlap).

These collections cover virtually the entire geographic range of the edwardsii species group.

Specimens of the edwardsii group were removed

from the collections and examined initially in

water with the aid of a stereomicroscope at magnifications of X 6 to X 50. Approximately 30 to 60

males and 10 to 25 females of each species were

selected from widely scattered samples for dissection and measurement. These specimens were prepared for dissection by digesting away all soft tissue

in heated aqueous KOH and then staining in

aqueous chlorozol-black-E. Stained material was

mounted in glycerine on glass slides and examined

with a compound or stereo microscope at magnifications of X 24 to X 200. All illustrations were

made from stained, glycerine-mounted specimens

with the aid of either a Wild M5 or M20 camera

lucida.

Length measurements were taken with an ocular

micrometer mounted in a stereomicroscope. All intact, identifiable specimens were immersed in water

and measured for carapace length (CL) at X 6 or

X 12; stained, glycerine-mounted specimens were

again measured for CL at X 12 or X 24. The left

petasmata of all stained, glycerine-mounted males

were dissected off and measured at X 100 along

their several distal lobes. The morphological details

of these are discussed under "Taxonomically Useful

Characters."

Species descriptions are based solely on sexually mature individuals. Values of measurements,

counts, and ratios are listed for each species after

its description. For counts and length measurements, the mean (x) and its 95% confidence limits

(cl) are presented along with the range (R) and

sample size (N). In the case of ratios, a median
NUMBER 256

(Md) rather than a mean value is listed. Citation

of material includes, in order, the lending institution, the expedition or cruise, the station or collection number, and the number of specimens and

their sex. Type specimens of new species have been

deposited in the National Museum of Natural History (NMNH), Smithsonian Institution, Washington, D. C, under the catalog numbers of the former

United States National Museum (USNM). Other

material deposited in NMNH and listed herein by

original collectors' numbers may be located through

NMNH's cross reference index. Abbreviations ap

pearing above for lending institutions, programs,

and gear are used in all citations of material examined.

Because of the wide variety of gear and sampling

methods used in collecting the material examined

in this study, no attempt is made to estimate densities. Hence, the maps depicting the geographical

distribution of species show only their presence or

absence at the sampling localities that yielded

Sergia or Sergestes. However, the relative abundance and frequency of occurrence of several species

have been determined from standardized samples

collected on EASTROPAC (ETP) Cruises 12 and

14 (Figure la,b). Both sets of samples were collected

at night with BMNs towed obliquely from about

200 m depth. ETP 12 sampled the sector of the

eastern tropical Pacific between 105° and 113°W,

whereas ETP 14 sampled the sector between 77°

and 92°W. Both cruises took place during late winter and early spring, 1967.

ABBREVIATIONS.—Appearing in "Taxonomically

Useful Characters," the key, species descriptions,

tables, and illustrations are the following morphological abbreviations:

AP

ASR

CL

COL

F

GC

LA

LC

LE

LI

LT

apical prominence

aperture to sperm

receptacles

carapace length

coxal lamella

foramen to body

cavity

genital cavity

lobus armatus

lobus connectons

lamina externa

lobus inermis

lobus terminalis

Maxl

Mxp3

Op

Ov

PA

PB

Per3

PM

PP

PU

PV

SP

maxilla 1

maxilliped 3

operculum

oviduct

pars astringens

processus basilis

pereopod 3

pars media

proximal projection

processus unifer

processus ventralis

sternal protuberance

ACKNOWLEDGMENTS.—I am most grateful to the

following individuals and their institutions for loan

of material examined in this study: A. Fleminger,

H. G. Snyder, Scripps Institution of Oceanography

(SIO), La Jolla, California; R. M. Laurs, Southwest

Fisheries Center (SWFC), National Marine Fisheries Service, La Jolla, California; R. H. Backus,

J. E. Craddock, R. L. Haedrich, D. L. Shores,

Woods Hole Oceanographic Institution (WHOI),

Woods Hole, Massachusetts; D. Damkaer, J. Bradford, R. Houbrick, Smithsonian Oceanographic

Sorting Center (SOSC), Smithsonian Institution,

Washington, D. C; J. Walters, Department of

Oceanography, University of Hawaii (UH), Honolulu, Hawaii; E. Bertelsen, T. Wolff, Universitetets

Zoologiske Museum (UZM), Copenhagen, Denmark; S. Pinkster, Instituut voor Taxonomische

Zoologie (ITZ), Universiteit van Amsterdam, the

Netherlands.

This paper is derived from a dissertation submitted in partial fulfillment of the requirements for

the Ph.D. degree at the University of California,

San Diego. E. Brinton, A. W. Ebeling, E. W. Fager,

A. Fleminger, J. A. McGowan, H. Stern, and B. A.

Taft served on my guidance committee and made

many useful suggestions towards improvement of

the dissertation. R. K. Johnson, M. D. Knight, and

J. H. Wormuth discussed various aspects of the

problem with me and provided many insights from

their own researches. I am especially grateful to E.

Brinton and A. Fleminger for their helpful advice

and criticisms throughout the course of this work

and also to F. A. Chace, Jr., and R. B. Manning for

their careful and thoughtful review of the final

version of the manuscript.

My thanks also go to H. G. Snyder for curatorial

aid and to K. Akutagawa for assistance in preparing

the illustrations.

This work was supported by a National Defense

Education Act Title VI Fellowship and by various

grants from the National Science Foundation, including the Sea Grant Program. Publication is

under the auspices of the U.S. Department of

Energy under contract No. EY-76-C-02-0016.

Genus Sergestes Milne-Edwards, 1830

DIAGNOSIS.—Sergestidae with specialized luminescent modifications of the gastrohepatic gland (organs of Pesta) but without dermal photophores.

Body semitransparent; color in life due primarily
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

to red stellate subcuticular chromatophores concentrated mainly on anterior part of body. Maxilliped

3 and pereopods 1, 2, and 3 elongate, slender, bearing stiff outstanding setae; pereopod 1 lacking

chela; pereopod 2 and pereopod 3 nearly always

with very small chelae; pereopod 4 and pereopod 5

without dactyli, pereopod 5 much shorter than

pereopod 4. Maxilla 1 usually with palp; maxilla

2 with two lobes; maxilliped 1 with segmented

palp. Possessing branchial lamellae as well as arthrobranchs; two arthrobranchs on pereopod 4,

none on pereopod 5. Petasma with processus ventralis not forked. (Modified from Yaldwyn, 1957,

according to Omori, 1974.)

PRESENT STATUS AND SUBDIVISIONS OF Sergestes.—

In a recent revision, Omori (1974) elevated Sergestes sensu stricto and Sergia, the two subgenera

composing Sergestes sensu lato (Burkenroad, 1940,

1945; Yaldwyn, 1957), to full genera. In Omori's

opinion, differences between the two taxa in luminescent structures and larval development justified

their separation at the generic level. Adults of the

revised genus Sergestes are distinguished by a semitransparent body and organs of Pesta. Sergia species

lack organs of Pesta, although many possess dermal

photophores instead. Most Sergia have fully pigmented cuticles, although some are only "half red."

Although clearly of common lineage, Sergestes is

readily divisable into six distinct species groups:

arcticus, corniculum, atlanticus, sargassi, vigilax,

and edwardsii (Yaldwyn, 1957). These groups are

easily distinguished from one another and appear

to be natural phyletic units.

Sergestes edwardsii Species Group

DIAGNOSIS.—Sergestes with outer uropod (Figure

3m) setose along entire outer margin. Antennular

peduncle (Figure 2b) with segment 3 subequal to

segment I; stylocerite immobile. Maxilliped 3 much

longer than pereopod 3 (Figure 2a); dactylus (Figure

5g) with six subsegments and two terminal spines.

Pereopod 5 (Figure 3/) without setae on leading

margins of distal two segments. Petasma (Figures Sg,

4a-c) with short, broad pars media and very short,

unarmed processus unifer and processus ventralis.

Organs of Pesta spherical in shape. Pereopod 3 with

minute branchial lamella located posterodorsally

to single plumose arthrobranch.

GENERAL MORPHOLOGY.—Body (Figure 2a) long,

slender, fragile. Abdomen, when extended, somewhat less than twice length of cephalothorax; segment 6 strongly compressed, about twice as long as

high. Carapace (Figure 2a,b) with short, acute hepatic and supraorbital spines, strong branchial, hepatic, and anterior ridges, and weak cervical and

postcervical sulci. Rostrum (Figure 2a,b) short,

ascendent, armed with single terminal tooth reaching barely beyond base of eyestalk.

Eyestalk (Figure 2b) lacking ocular tubercle;

brown cornea wider than stalk.

Antennular peduncle (Figure 2a,b) about threefourths as long as carapace; outer margin of segment 1 considerably longer than that of segment 2

but only slightly longer than that of segment 3;

stylocerite (Figure 2b) short, acute, immobile. Antennular outer flagellum about three times as long

as peduncle; inner flagellum in female (Figure 2d)

short, simple; inner flagellum in male (clasping

organ) (Figure 2c) with deep proximomesial notch

and opposed curved spine.

Antennal peduncle armed with distolateral tooth

on basal segment (Figure 2b). Antennal flagellum

more than twice length of body, divided into proximal and distal parts by short section of annuli forming a double bend (cf. Foxton, 1969). Scaphocerite

(Figure 2b) distally tapered, reaching slightly beyond antennular peduncle, armed with small terminal tooth.

Mandibular cutting blades (Figure 2e,f) asymmetrical; right blade anteriorly armed with single

acute tooth occluding with deep notch on left

blade; both blades possessing posterolateral molarlike processes. Mandibular palp (Figure 2e) reaching to distal segment of antennular peduncle, first

of three segments very short.

Maxilla 1 (Figure 2g) with two paddle-shaped

lobes distally bearing numerous stiff setae; outer

lobe larger, usually with short fingerlike palp on

proximolateral margin. Maxilla 2 (Figure 2h) with

lamellar outer lobe (scaphognathite), fingerlike

inner lobe, and three mesial endites.

Maxilliped 1 (Figure 2i) with flat, semirectangular inner and outer lobes, lamellar exopodite, and

small epipodite (not shown); outer lobe with threesegmented leglike palp, segment 2 divided into two

unequal subsegments. Maxilliped 2 with very short

exopodite (not shown) and heavily bristled sevensegmented endopodite (Figure 2/) flexed posteriorly
NUMBER 256

at merocarpal articulation. Maxilliped 3 (Figure 2k)

much stouter and longer then pereopod 3 and over

twice as long as carapace (Figure 2a); propodus with

two subsegments, first nearly twice as long as second; dactylus (Figure 5g) with six subsegments, first

slightly shorter than second, proximal two together

about as long as distal four; inner margin of dactylus bearing constant number of large spines and

variable number of shorter ones, large spines consisting of single long distal spines on subsegments

1 to 5 and single shorter mesial spines on subsegments 1 and 2; outer margin of dactylus bearing

single distal spines of variable length on subsegments 1, 2, and 4 and one or two short mesial

spines on subsegments 1 and 2; subsegment 6 bearing two terminal spines.

Pereopod 1 (Figure 2/) about two-thirds as long

as pereopod 2 (Figure 3a); pereopod 3 (Figure 3c)

slightly longer than pereopod 2; pereopod 4 (Figure

Se) about equal in length to pereopod 1; pereopod

5 (Figure 3/) about half as long as pereopod 4. Pereopod 1 armed with numerous barbed spines at carpopropodal articulation (Figure 2m). Pereopod 1

and pereopod 2 armed with curved tooth on lateral

margin of ischium. Chelae (Figure Sb,d) with

dactylus slightly longer than palm, both dactylus

and palm bearing terminal tufts of long setae. Pereopod 4 and pereopod 5 laterally flattened, bearing

natatory setae on all but leading margin of distal

two segments.

Maxilliped 2 with branchial lamella and podobranch. Maxilliped 3 and pereopods 1 to 3 each

with large, plumose anterior arthrobranch and minute posterodorsal branchial lamella. Pereopod 4

with anterior arthrobranch about twice as long as

posterior arthrobranch.

Organs of pesta consisting of single anterior midventral organ and three pairs positioned anterolaterally, midlaterally, and posterolaterally (cf. Foxton, 1972).

Thelycum of female (Figure Ad) consisting of

modified portions of pereopod 3 coxa and thoracic

sternite 6. Pereopod 3 coxa with broad, flat proximal projection at proximomesial corner, low apical

prominence at distomesial corner, and elongate,

greatly hollowed genital cavity containing ovipore

occupying most or all of intervening mesial margin;

narrow, membranous coxal lamella protruding mesially from coxosternal articulation. Thoracic sternite 6 anteriorly forming operculum projecting posteriorly over common slitlike aperture of sperm

receptacles (Figure 4e); posterior half of sternite

with low transverse ridge terminating beneath proximal projections on coxa in two low anteriorly

directed sternal protuberances and with shallow

groove extending along midline between transverse

ridge and sperm receptacle aperture.

Petasma of male emerging from proximomesial

margin of pleopod 1 (Figure 3g) and interlocking

with member of opposite side by means of cincinulli on inner margin of pars astringens. Pars externa with flat, rectangular lamina externa and

short, distally rounded processus unifer. Processus

basilis large, triangular, bluntly rounded mesially

(Figure 4a). Pars media very short, wide, bearing two or three conspicuous lateral projections.

Processus ventralis very short (Figure Ab,c). Lobus

armatus elongate, usually bilobed, directed distally

and/or laterally. Lobus connectons with one to

three short, rounded lobes. Lobus terminalis with

elongate anterior and posterior lobes. Lobus inermis

directed distally, usually extending beyond outer

lobes.

Pleopod 1 of female (Figure $h) armed with

curved tooth at about same location on propodus

as origin of petasma of male. Pleopod 2 in both

sexes armed with small tooth near midpoint of

inner margin of propodus; propodus in male (Figure 3;) armed with second, slightly curved tooth at

distomesial corner. Appendix masculina (Figure

3A) single, paddle-shaped lobe bearing spines of

varying length on distal margin.

Telson (Figure 3/) distally rounded, lacking terminal spines. Outer uropod (Figure 3m) about onethird longer than inner uropod and setose along

entire outer margin.

TAXONOMICALLY USEFUL CHARACTERS.—Species

of the edwardsii group are morphologically very

uniform, differing significantly only in the features

discussed below.

Carapace Length (CL): Although overlapping to

varying degrees in CL, species differ significantly in

mean value of the measurement. In all species, females tend to be somewhat larger than males, and,

hence, the two sexes are considered separately in

this feature. CL was measured from the tip of the

rostrum to the dorsal midpoint of the posterior

margin of the carapace.

Maxilla 1 (Maxl) Palp: Although relatively large

in the majority of species, in Sergestes edwardsii
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 1.—Spination of the Mxp3 dactylus in the edwardsii group (additional data for columns

four and five in species descriptions)

Species

S. edwardsii

S. consobrinus.

California Current

Form

S. consobrinus.

Central Form

S. tantillus

S. semissis

S. orientalis

S. qibbilobatus

Subseqment 1

3/4 length

subsegment 2;

1 mesial spine

J length subsegment 2 ;

1 mesial spine

Distal spine <

| length

subsegment 2;

1 mesial spine

Distal spine 2

3/4 length

subsegment 2;

1 mesial spine

Distal spine 2

3/4 length

subsegment 2

1 mesial spine

Distal spine <

length subsegment 2;

1 mesial spine

Distal spine <

1/4 length subsegment 2; 2

mesial spines

As in orientalis

Outer Marqin

Subseqment 2

length subsegments 3 + 4;

1 mesial spine

total length

subsegments

3+4 ; 1 mesial

spine

Distal spine <

total length

subsegments 3 +

4; 1 mesial

spine

Distal spine ~

total length

subsegments 3 +

4+5 ; 1 mesial

spine

Distal spine ~

total length

subsegments 3 +

4; 1 mesial

spine

Distal spine ~

length subsegment 3 ;

1 mesial spine

Distal spine <

1/2 length

subsegment 3;

2 mesial spines

As in orientalis

Subseqment 4

3/4 length

subsegment 5

very short

Distal spine

very short

Distal spine

~ 3/4 length

subsegment 5

Distal spine --

length subsegment 5

Distal spine

minute

Distal spine

minute

As in orientalis

Inner Marqin

Total No.Spines

rf: 34-43

8:35-46

<f:27-37

8:36-42

rf:33-41

8:38-47

8:29-41

<f: 50-68

«:53-59

rf:36-49

8:46-57

rf:33-40

8:36-42

j. 33-45

5:35-42

rf:39-48

8:40-48

Terminal Spines

Lenqth Inner/Lenqth Outer

rf:0.85-1.20

¥:0.59-1.17

d^O. 52-0.83

¥:0.50-0.95

rf:0.49-0.92

cf:0.75-1.10

J:0. 86-1.15

8:0.77-1.00

rf:0.76-1.19

9:0.44-1.95

rf:0.37-1.00

8:0.40-0.89

9:0.40-0.59

^:0.43-0.80

8:0.40-0.71

and the Central form of S. consobrinus this structure is usually vestigial, and occasionally entirely

absent.

Maxilliped 3 (Mxp3) Dactylus: Aspects of the

spination of this structure can be of use in separating species of the group (Table 1). Unfortunately,

the Mxp3 is often damaged or missing in preserved

specimens. Features exhibiting interspecific differences are the number of spines on the inner margin,

the length of the outer distal spines on subsegments

1, 2, and 4, the number of outer mesial spines on

subsegments 1 and 2, and the relative length of the

terminal spines on subsegment 6. Certain of these

features also show ontogenetic and sexual differences; i.e., within species, inner margin spines tend

to be more numerous and outer margin spines relatively shorter in adult females than in adult males

or subadults of either sex. When the sexes are considered separately, significant interspecific differences are discernible in the mean or median values

of these features, yet considerable overlap still occurs

in the data. Characters of the Mxp3 dactylus should

be used with caution in separating species of the

edwardsii group.

Pereopod 3 (Per3) Coxa in Female: Species differ

slightly but consistently in size and shape of the

proximal projection (PP), apical prominence (AP),

and genital cavity (GC). Unfortunately, these structures can be easily observed only in cleared and

stained specimens from which the thelyca have been

carefully dissected (see "Methods"), and this inaccessibility minimizes their diagnostic value.
NUMBER 256

Petasma: Interspecific differences occur in the

shape, configuration, and, in some cases, length and

armature of the lobus inermis (LI), lobus terminalis

(LT), lobus connections (LC), lobus armatus (LA),

processus ventralis (PV), and pars media (PM).

Diagnostically, these are the most useful characters

within the group. Features measured include the

LI, the anterior and posterior lobes of the LT, the

outer lobe of the LC, and LA (cf. Figure 4b,c). The

LI, LT, and LC were measured distally from a

baseline connecting the inflection points on the

inner and outer margins of the PM. The LA, a

laterally directed lobe, was measured along its axis

from the inflection separating it from the LC. To

standardize these measurements against size effects,

they are presented in the text as ratios (LI/CL, LT

anterior/LI, LT posterior/LI, LC outer/LI, LA/

LI). Scattergrams of LI length and LT anterior lobe

length versus CL are useful in demonstrating differences in the petasmata of closely related populations (Figures 8, 11, 18).

Males usually were identified readily by examination of their petasmata. However, not all females

from regions of overlap could be separated to species because of the frequent absence of easily accessible diagnostic features.

Key to Species of the edwardsii Group

ADULT MALES

1. No inflection at base of LI; LT posterior lobe thumblike, unarmed, directed posteriorly

(Figure 14b-d); inhabiting northern Indian Ocean, Bay of Bengal, Arabian Sea

(Figure 15) 5. S. semissis

Strong inflection at base of LI; LT posterior lobe cylindrical or fingerlike, armed distally

with single tooth, directed distally 2

2. LI bearing distal protuberances; LI anterior lobe lamellar, twisted, armed distaily

with single exposed hook 3

LI without distal protuberances; LT anterior lobe fingerlike, armed with several hooks 5

3. LI posterior lobe with distal end strongly bent laterally; PV not reaching inflection

between LA inner and outer lobes (Figure 19b, c); inhabiting central and eastern tropical Pacific (Figure 20) 8. S. gibbilobatus

LI posterior lobe with distal end not bent laterally, PV reaching to or beyond inflection

between LA inner and outer lobes 4

4. LC usually trilobed, outermost lobe about equal in size to innermost lobe (Figure 16b, c);

inhabiting tropical Indian Ocean, Indo-Australian archipelago, western tropical Pacific,

Hawaiian archipelago (Figure 17) 6. $. orientalis

LC usually bilobed; outermost lobe, when present, tending to be smaller than innermost lobe

(Figure I6g, h); inhabiting eastern tropical Pacific (Figure 17) 7. S. geminus

5. LA and LC both single lobes (Figure 12b, c); inhabiting central and eastern tropical Pacific

(Figure 13) 4. S. tantillus

LA and LC bilobed 6

6. LA outer lobe directed laterally, distal half bent forward onto proximal half 7

LA outer lobe directed distolaterally, distal half not bent forward onto proximal half 8

7. Outer distal spine on subsegment 4 of Mxp3 dactylus very short; outer terminal spine on

subsequent 6 about two-thirds length on inner (Figure 9g); inhabiting outer California

Current region (Figure 10) 3a. S. consobrinus, California Current form

Outer distal spine on subsegment 4 very long; terminal spines on subsegment 6 subequal

(Figure 9h); inhabiting central north Pacific (Figure 10) ....3b. S. consobrinus, Central form

8. LT anterior lobe usually longer than posterior lobe (Figure 5b); outer distal spine on subsegment 4 of Mxp3 dactylus long, terminal spines on subsegment 6 subequal (Figure 5g);

inhabiting tropical Atlantic (Figure 6) 1. S- edwardsii

LI anterior lobe usually shorter than posterior lobe (Figure 5c); outer distal spine on subsegment 4 of Mxp3 dactylus very short, outer terminal spines on subsegment 6 noticeably

unequal (Figure 5/i); inhabiting eastern tropical Pacific (Figure 6) 2. S. brevispinatus

ADULT FEMALES

1. Two mesial spines on outer margin of either or both subsegments 1 and 2 of MxpS

dactylus - 2
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Key to Species of the edwardsii Group (cont'd)

One mesial spine on outer margin of subsegments 1 and 2 4

2. Per3 coxa with distinct bulge on distal margin of PP (Figure 16/) 3

Per3 coxa without distinct bulge on distal margin of PP (Figure 19/»); inhabiting central

and eastern tropical Pacific (Figure 20) 8. S. gibbilobatus

3. Inhabiting tropical Indian Ocean, Indo-Australian archipelago, western tropical Pacific,

Hawaiian archipelago (Figure 17) 6. S. orientalis

Inhabiting eastern tropical Pacific (Figure 17) 7. S. geminus

4. Outer distal spine on subsequent 4 of Mxp3 dactylus very short 5

Outer distal spine on subsegment 4 long, reaching to or beyond midpoint of subsegment ....7

5. GC of Per3 coxa extending distally to AP (cf. Figure 4d) 6

GC not extending distally to AP (Figure 14g); inhabiting northern Indian Ocean, Bay of

Bengal, Arabian Sea (Figure 15) 5. S. setnissis

6. GC of Per3 coxa broad, viewed ventrally; PP long, acute (Figure 9i). Inhabiting outer

California Current region (Figure 10) 3a. S. consobrintis, California Current form

GC relatively narrow, viewed ventrally; AP relatively short, blunt (as in S. edwardsii, cf.

Figure 5i); inhabiting eastern tropical Pacific (Figure 6) 2. S. brevispinatus

7. Mxp3 dactylus with 50 or more spines on inner margin (Figure I2d); GC of Per3 coxa with

indentation on dorsal margin (Figure 12e); inhabiting central and eastern tropical Pacific

(Figure 13) 4. S. tantillus

Mxp3 dactylus with less than 50 spines on inner margin; GC without indentation on dorsal

margin 8

8. GC of Per3 coxa very broad, viewed ventrally (Figure 9;); inhabiting central north Pacific

(Figure 10) 3b. S. consobrintis, Central form

GC relatively narrow, viewed ventrally (Figure 5i); inhabiting tropical Atlantic (Figure 6)

1. S. edwardsii

1. Sergestes edwardsii Kroyer, 1855

FIGURES 2e,f,h-m, 3, Aa,b,d,e, 5a-c,g,i,j, 6, 8, 216

Sergestes Edwardsii Kroyer, 1855:28; 1859:246, 277, 284, 285,

pi. 4: fig. 9a-*.-Hansen, 1896:961 [in part]; 1919:26, pi.

2: fig. 3.—Illig, 1914:363, fig. 25 [in part]; 1927:320, figs.

86, 89, 90, 91 [in part].

Sergestes occulataus Kroyer, 1855:28; 1859:243, 277, 284, 285,

pi. 3: fig. 5a-/.—Bate, 1888:406, pi. 74: fig. 1 [in part].—

Hansen, 1896:963

Sergestes brachyorrhos Kroyer, 1859:272, 281, 284, 285, pi.

5: fig. 13a,fo.

Sergestes edwardsi Bate, 1888:403, pi. 73: fig. 2 [in part].—

Borradaille, 1916:81:—Sund, 1920:27.-Hansen, 1922:182,

pi. 11: figs, la-i, 2a-/.-Gurney and Lebour, 1940:62, fig.

56.—Dennell, 1940:314, 320.

Sergestes (Sergestes) edwardsi.—Yaldwyn, 1957:8.—Milne, 1968:

29-31.—Crosnier and Forest, 1973:307, 320-322, figs. 108b,

lO9b,c, 110c,d.

TYPES.—Although Kroyer did not publish type

specimens or material examined in his description

of S. edwardsii, three of the specimens on which the

description is based have been labeled "Types."

The available data on these specimens, which were

loaned to me by the UZM, are summarized:

(1) 1 $ , 3.5 mm CL, collected in the Atlantic at

20°N, unspecified longitude; (2) 1 $ , 3.5 mm CL,

collected in the Atlantic at 10°22'N, 21°16'W;

(3) ltf, 4.8 mm CL, collected in the Atlantic at

7°N, 30°W. I have designated the last specimen

listed, the only male in the series, as the lectotype.

ADDITIONAL MATERIAL— WHOI, Chain 35: RHB 953<13),

958(1 £ , 1$), 959(13), 962(7 3 3 , 8$$) , 966(6$?), 970

(2$ $, 3 $ $), 975(1$), 980(8 3 3 , 12$ $). WHOI, Atlantis

II 13: RHB 1026(2 3 3). WHOI, Atlantis II 20: RHB

1201(13, 5$$) , 1203(53 3 , 3$$) , 1204(43 3 , 17$$) ,

1206(2 3 3,1$) , 1207(12 $ $), 1208(3 3 3 ,21 $ $), 1209(7 3 8 -

14$$) , 1210(13,1$), 1213(2$$), 1214(37 3 3,32$$) ,

1215(43 3 , 17$$) , 1216(13, 2$$) , 1217(43 3), 1219(13-

7 $ $), 1222(1 3). WHOI, Chain 60: RHB 1253(1 $, 1 $),

1257(4 3 3), 1258(13, 6$$) , 1267(1$), 1271(7$$), 1272

(23 3 , 3$$) , 1273(3$$), 1276(13, 1$), 1277(6$$),

1282(63 3 , 11$$) , 1290(83 3 , 16$$) , 1291(2$$), 1312

(23 3 , !?)> 1314(23 3 , 2$$) . WHOI, Chain 72: RHB

1505(13), 1516(13, 5$$) . WHOI, Atlantis II 49: RH B

1935(13), 1942(2$ $).

T h e material listed is deposited in NMNH.

DESCRIPTION.—Maxl palp (Figure 5;) usually vestigial and without setae, occasionally entirely absent.

Mxp3 dactylus (Figure 5g, Table 1) with single

mesial spines on outer margins of subsegments 1

and 2. Outer distal spine on subsegment 1 usually

reaching to origin of outer distal spine on subsegment 2; outer distal spine on subsegment 2 usually
NUMBER 256

c,d,f,g,h,i m

FIGURE 2.—Sergestes geminus, $, 6.4 mm CL: a, habitus lateral; b, anterior cephalothorax,

dorsal; c, distal end of $ antennular flagellum showing clasper, ventral. 5. brevispinatus,

9, 6.3 mm CL: d, distal end of $ antennular peduncle showing lower flagellum, ventral.

S. edwardsii, $, 5.1 mm CL: e, mandibles (left palp incomplete), ventral; /, mandibles (palps

incomplete), dorsal. S. gibbilobatus, $, 6.9 mm CL: g, left maxilla I, anterior. S. edwardsii,

$, 5.1 mm CL: h, left maxilla 2, anterior; i, left maxilliped 1, anterior; ;, left maxilliped 2,

lateral; k, left maxilliped 3, lateral; /, left pereopod 1, lateral; m, articulation between carpus

and propodus of left pereopod 1, mesial.
10

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 3.—Sergestes edwardsii, $, 5.1 mm CL: a, left pereopod 2, lateral; b, chela of left

pereopod 2, lateral; c, left pereopod 3, lateral; d, chela of left pereopod 3, lateral; e, left pereopod 4, lateral; /, left pereopod 5, lateral; g, $ pleopod pair 1 with petasraata attached, posterior. 9, 6.1 mm CL: h, $ left pleopod 1, posterior. $, 5.1 mm CL: i, $ left pleopod 2,

mesial: /, $ left pleopod 2, posterior; *, $ left appendix masculina, mesial; /, telson, ventral;

m, left uropod, ventral.
NUMBER 256 11

a.

UJ

hO

CE

o

LJ

h00

O

CL

LI

r

cr

g

cc

UJ

1—

<

_ l

1.0 mm

0.7 mm

d,e

0.5 mm

b,c

9, 6.3 mm CL: d, $ thelycum and adjacent features (bracket on left side delimits sixth thoracic segment), posteroventral view; e, sperm receptacles (stippled, lying beneath line drawing

of external features of thelycum), posteroventral.

reaching beyond end of subsegment 4; outer distal

spine on subsegment 4 usually reaching beyond

midpoint of subsegment 5; outer terminal spine on

subsegment 6 usually more than three-fourths

length of inner spine. Distal spines on outer margin

of subsegments 1, 2, and 4, and outer terminal

spine on subsegment 6 tending to be relatively

shorter in female.

Per3 coxa in female (Figure hi) with short, blunt

PP and low, blunt AP; GC narrow in ventral view,

extending distally to DP.

Petasma (Figure ba-c) with LI fingerlike, strongly

inflected at proximomesial margin, sometimes

slightly expanded distally. LT lobes both fingerlike;

anterior lobe distally rounded, armed both anteriorly and posteriorly with large hooks; posterior

lobe slenderer, usually slightly shorter than anterior

lobe, armed with single large terminal hook. LC

bilobed; inner lobe low, rounded, armed with row

of large hooks extending longitudinally along posterior face, over distal margin, and then laterally

along anterior face to point below base of outer

lobe; outer lobe bulbous, directed distolaterally,

distally armed with several small hooks. LA bilobed; inner lobe low, rounded, distally covered

with numerous minute hooks; outer lobe slender,

elongate, directed distolaterally, armed with large

terminal hook and lateral row of four to six smaller
12

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

OMS-2

a,d,g,h,j,k b.c.e.f

FIGURE b.—Sergestes edwardsii, $, 4.5 mm CL: a, left petasma, posterior; b, c, capitulum of

left petasma, posterior and anterior. 5. brevispinatus, $ , 5.7 mm CL: d, left petasma, posterior; e, f, capitulum of left petasma, posterior and anterior. S. edwardsii, $, 5.1 mm CL:

g, dactylus of left Mxp3, mesial (OMS-1, -2 = outer mesial spines of subsegments 1, 2; ODS-1,

-2, -4 = outer distal spines of subsegment I, 2, 4). S. brevispinatus, $, 5.4 mm CL: h, left

Mxp3 dactylus, mesial. S. edwardsii, §, 6.3 mm CL: i, thelycum, posteroventral. S. edwardsii,

$, 5.1 mm CL: ;, left Maxl, anterior. S. brevispinatus, $, 5.4 mm CL: k, left Maxl, anterior.
NUMBER 256

13

hooks on proximoanterior margin. PV extending to

about level of inflection between LC and LA. PM

with three conspicuous projections on lateral margin.

CL

MEASUREMENTS, COUNTS, AND RATIOS

x (mm) 95% cl (mm) R (mm)

4.6 ±0.1 3.6-5.9

5.5 ±0.1 4.0-7.0

Total number of spines on Mxp3 dactylus inner margin

x 95% cl R

$ 37.2 ±1.8 34-43

9 38.4 ±2.4 35-46

N

112

259

N

10

10

Length of inner/length of outer terminal spines on Mxp3

dactylus

s

9

Petasma ratios

LI/CL

LT anterior/LI

LT posterior/ LI

LC outer/LI

LA/LI

Md

1.00

0.89

Md

0.136

0.62

0.58

0.51

0.48

R

0.85-1.20

0.59-1.17

R

0.106-0.153

0.54-0.71

0.48-0.67

0.40-0.58

0.35-0.36

N

15

10

N

32

32

32

32

31

DISTRIBUTION.—Sergestes edwardsii is broadly distributed throughout the tropical Atlantic, Caribbean, and Gulf of Mexico (Figure 6). Records at

relatively high northern latitudes in the western

Atlantic are probably the result of transport by the

Gulf Stream.

2. Sergestes brevispinatus, new species

FICURES Id, 5d-f,hjt; 6-8, 216

HOLOTYPE.—USNM 155056, adult tf, 6.0 mm

CL.

TYPE-LOCALITY.—Sorted from micronekton collection taken at ETP 14 sta 081 (ll°02'S, 81°41'W);

14 Feb 1967; nighttime oblique tow with BMN

from ca. 200 m.

ALLOTYPE.—USNM 155058, adult 9, 9.0 mm CL;

sorted from micronekton collection taken at

ETP 14 sta 091 (14°48'S, 79°58'W); 16 Feb 1967;

nighttime oblique tow with BMN from ca. 200 m.

PARATYPES.—USNM 155057, 5 adult and subadult cfcT, 5.5, 5.7, 5.8, 5.9, 6.0 mm CL; from same

collection as holotype. USNM 155059, 5 adult and

subadult $ ? , 7.4, 7.5, 7.6, 8.4, 9.0 mm CL, and 1

adult c?, 5.9 mm CL; from same collection as

allotype.

ADDITIONAL MATERIAL.—SIO, Shellback: 13(1 $). SIO,

Eastropic: 16(1 ^ , 9 9 9). SIO, Anton Brunn 12: 65-603(15).

65-606(7 $ $), 65-608(1 £). SWFC, ETP 12: 059(32 $ $, 19).

084(1 $), 094(1 $), 106(2$ $), 118(1 3). SWFC,ETP 14: 014(1 3),

018(115 5), 022(75 5. 4 9 9). 027(15). 043(5 5 5), 051

(215 5, 29 9). 081(19), 086(10 5 5), 091(205 5, 19).

099(25 5. 19), 106(25 5), 110(1$), 120(35 5), 124(35 5,

19). 132(2 5 5). 138(95 5, 3 9 9). 154(25 5). 232(15).

240(15), 247(115 5, 19), 255(195 5, 49 9), 263(4 5 5),

271(1 5), 287(1 5,499) . 303(4 5 5 , 10 9 9), 326(1 5).

The material listed is deposited in the SIO Zooplankton

Collections.

DESCRIPTION.—Maxl palp (Figure bk) relatively

large, with one or two distal setae.

Mxp3 dactylus (Figure bh, Table 1) with single

mesial spines on outer margins of subsegments 1

and 2. Outer distal spine on subsegment 1 seldom

reaching beyond subsegment 2; outer distal spine

on subsegment 2 seldom reaching beyond subsegment 4; outer distal spine on subsegment 4 very

short; outer terminal spine on subsegment 6 usually

less than three-fourths length of inner terminal

spine. Distal spines on outer margin of subsegments

1, 2, and 4 and outer terminal spine on subsegment

6 tending to be relatively shorter, and inner margin

spines more numerous in female.

FICURE 6.—Geographical distribution of records of Sergestes

edwardsii and S. brevispinatus (line through solid circle =

literature records; see Crosnier and Forest, 1973).
14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

ETP 12

W)

ETP 14

(77° - 92° W)

ETP 12

W)

ETP 14

(7 7°-92° W)

FICURE 7.—Based on collections from ETP cruises 12 and 14, representing the western and

eastern sectors of the eastern tropical Pacific, respectively, four species of edwardsii group

compared: a, frequency of occurrence; b, relative abundance (frequency of occurrence = the

percentage of the total number of collections made on each cruise in which an individual species

occurred; relative abundance = the percentage of the total number of specimens taken on each

cruise representd by an individual species; 1 = S. brevispinatus; 2 — S. tantillus; 3 = 5. geminus;

4 = 5. gibbilobatus).

Per3 coxa of female as in S. edwardsii (cf. Figure

5i).

Petasma (Figure 5d-f) very similar to that in S.

edwardsii but differing in following features: LI

usually more rounded proximally and seldom expanded distally; LT posterior lobe usually slightly

longer than anterior lobe (Figure 8c); LC inner lobe

armed with hooks posteriorly and distally, but not

anteriorly; LA outer lobe armed with six to eleven

hooks along proximoanterior margin; LI and LT

anterior lobe tending to be longer relative to CL

(Figure Ba,b).

CL

MEASUREMENTS, COUNTS, AND RATIOS

x (mm) 95% cl (mm) R (mm) N

5.0 ±0.1 3.6-6.7 193

6.6 ±0.3 4.7-8.7 44

Total number of spines on Mxp3 dactylus inner margin

* 95% cl R N

S 33.8 ±2.3 27-37 10

$ 39.3 ±1.7 36-12 10

Length of inner/length of outer terminal spines on Mxp3

dactylus

Md R N

0.70

0.65

Petasma ratios

Md

LI/CL 0.113

LT anterior/LI 0.66

LT posterior/LI 0.71

LC outer/LI 0.69

LA/LI 0.67

0.52-0.83

0.50-0.95

R

0.091-0.023

0.57-0.79

0.58-0.80

0.53-0.80

0.51-0.81

10

12

N

25

25

25

25

25
NUMBER 256 15

0.70 -

0.60 -

0.50

S. edwardsii •

5. brevispinatus O

O o

O O

o o

ooo

o

o o

o •

o o

—

E

E

HLU

OD

o_J

§ 0.40

oc

UJ

t -

2

 I

X

to

ill

_J

5. edwardsii

S. brevispinatus

•

> • • •

• • •

o o

•

o

•

1

•

• o

•

• •

•

o c

o

0

9

o *

CD

O

O CO

o

«O« CO

o

o

•

o

-

o

-

oo

5.00

CL ( mm)

6.00

0.50

5.00

CL (mm)

6.00

S. edwardsii •

5. brevispinatus O

• • O

O o

O O

O

• • O O

• O

• «O» O O

• o o o

• o o -

c 0.40

LENGTH POSTERIOR LOBE LT(mm)

FIGURE 8.—Sergestes edwardsii and 5. brevispinatus compared for certain relationships: a, LI

length and CL; b, LT anterior lobe length and CL; c, LT anterior and posterior lobe lengths.

0.50

DISTRIBUTION.—Sergestes brevispinatus is clearly

indigenous to the eastern tropical Pacific (Figure 6).

Judging from its frequency of occurrence in collections from ETP 12 and 14 (Figure la), this species

appears to prefer oceanic waters close to the continental margin of Central and South America. It is

by far the most abundant of the four edwardsii

species present in ETP collections from that sector

of the eastern tropical Pacific (Figure 76).

REMARKS.—Size of the Maxl palp and spination

of the Max3 are the most obvious characters separating S. brevispinatus from S. edwardsii. However,

differences in these features may be simply a consequence of differing developmental rates resulting

from different levels of food in their respective geographical habitats (cf. Reeve, 1969). This interpretation is supported by the generally smaller size of S.

edwardsii and the similarity of immature S. brevi-
16

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

spinatus to mature S. edwardsii in features of the

Maxl palp and Mxp3 dactylus. It should be noted,

however, that the relative importance of environmental versus genetic factors in bringing about

these interspecific differences remains a matter of

speculation. Moreover, differences in the petasmata

of the two forms, although relatively inconspicuous,

do not appear to be size related and, thus, are more

likely to be of genetic origin.

My decision to recognize S. brevispinatus as a

separate species is based on biogeographical, as well

as morphological grounds. S. edwardsii is restricted

to the tropical Atlantic, whereas S. brevispinatus is

endemic to the eastern tropical Pacific, and thus,

there is little likelihood of gene flow between them

now or in the recent past. Furthermore, the eastern

tropical Pacific supports many endemic pelagic

species while excluding many of their more widespread tropical congeners. The region's unique and

exclusive pelagic fauna may be a consequence of

the extremely low oxygen tensions characterizing

its near surface waters (Knauss, 1963), a phenomenon quite possibly requiring special physiological

and behavioral adaptations in the mesopelagic

species occurring there. For these reasons, I think

that it is likely that S. edwardsii and S. brevispinatus are reproductively isolated and, thus, should be

considered separate species.

ETYMOLOGY.—The specific name is derived from

the latin brevis (short) plus spinatus (spined).

It refers to the shortness of the outer distal and

outer terminal spines on the Mxp3 dactylus of the

new species relative to the same spines in 5.

edwardsii.

3. Sergestes consobrinus Milne, 1968

FIGURES 9-11, 216

Sergestes (Sergestes) consobrinus Milne, 1968:26-33, figs. 5-9.

TYPE-LOCALITY.—Great Bear cruise 199, IKMT

haul 227 (off southern California: 33°44'N, 124°53'

W).

PRELIMINARY REMARKS.—Milne's (1968) description of this species is based on specimens collected

from the outer sector of the California Current system. Collections from, the central North Pacific

examined in the present study contained individuals similar, but not identical, in morphology to

S. consobrinus from the California Current region.

For reasons discussed below, I am not recognizing

these morphologically divergent populations at the

present time as separate species but rather as geographical variants, termed the "California Current" and "Central" forms, respectively. The two

forms are described separately.

3a. California Current Form

FIGURES 9a-c,g,i, 10, 11, 21 b

MATERIAL— SIO, Pelagic Area Survey: 8(2$ $, 1 9),

11(13, 5 9 $)- 1*(23 3)- SIO, Tethys: 4(1 $). SIO, CalCOFI

H6204: 60.100(4$ 9), 60.120(19), 60.160(4 9 9), 60.180(4 3 $,

19), 90.120(5 3 3), 90.160(13), 100.80(53 3 , 3 9 9), 100.90

(13 , 3 9 9), 100.100(63 3 , 12 9 9), 100.120(4 3 3), 100.120

(13 , 2 9 9), 110.160(13), 120.45(19), 120.90(19). 120.90

(13 , 2 9 9). SIO, CalCOFI 7008: 90.145i/2(93 3 , 8 9 9),

120.45(8 3 3 , 119 9), 120.120(12 9 9), 120.120i/2(3 3 3, 8 9 9).

The material listed is deposited in the SIO Zooplankton

Collections.

DESCRIPTION.—Maxl palp relatively large, with

one distal seta (cf. S. brevispinatus, Figure 5k).

Mxp3 dactylus (Figure 9g, Table 1) with single

mesial spines on outer margins of subsegments 1

and 2. Outer distal spine on subsegment 1 seldom

reaching beyond midpoint of subsegment 2; outer

distal spine on subsegment 2 seldom reaching much

beyond juncture of subsegments 3 and 4; outer

distal spine on subsegment 4 very short, seldom

reaching to subsegment 5. Outer terminal spine on

subsegment 6 typically one-half to two-thirds as

long as inner spine. Distal spines on outer margin

of subsegments 1, 2, and 4 and outer terminal spine

on subsegment 6 tending to be relatively shorter

and inner margin spines more numerous in female.

Per3 coxa in female (Figure 9i) with long, broad

PP and low, blunt AP; GC broad in ventral view

and extending distally to AP.

Petasma (Figure 9a-c) with LI stout, fingerlike,

strongly inflected at proximomesial margin. LI

lobes both fingerlike; anterior lobe stouter and

much longer than posterior lobe, armed both anteriorly and posteriorly with hooks; posterior lobe

armed with single terminal hook. LC bilobed:

inner lobe low, rounded, armed posteriorly with

longitudinal row of large hooks; outer lobe bulbous, directed distolaterally, armed distally and

posteriorly with hooks of varying size. LA bilobed:

inner lobe low, rounded, covered distally with numerous minute hooks; outer lobe slender, directed
NUMBER 256 17

laterally, distally flexed onto anterior face, armed

with large terminal hook and lateral row of six to

11 large hooks on proximoanterior margin. PV

reaching to level of inflection between LC and LA.

PM with three conspicuous lateral projections.

MEASUREMENTS, COUNTS, AND RATIOS

CL

x (mm)

5.6

6.6

95% cl (mm)

±0.2

±0.2

R (mm)

3.8-6.7

4.4-8.1

Total number of spines on Mxp3 dactylus inner margin

x 95% cl R

39.8 ±2.1 33-41

41.3 ±2.3 38-47

N

60

79

N

10

10

Length of inner/length of outer terminal spines on Mxp3

dactylus

Petasma ratios

LI/CL

LT anterior/LI

LT posterior/LI

LC outer /LI

LA/LI

Md

0.66

0.55

Md

0.103

0.79

0.66

0.69

0.56

R

0.49-0.92

0.48-0.72

0.089-0.119

0.69-0.86

0.55-0.77

0.57-0.87

0.48-0.52

N

10

10

N

27

27

27

27

27

DISTRIBUTION.—This geographical form of S.

consobrinus appears to be restricted to the outer

sector of the California Current region.

LC LI

1.0 mm 0.7 mm 0.5 mm

o,d,g,h i,j b,c,e,f

FIGURE 9.—Sergestes consobrinus, California Current form, $, 6.1 mm CL: a, left petasma,

posterior; b, c, capitulum of left petasma, posterior and anterior. Central form, $, 4.9 mm

CL: d, left petasma, posterior; e, f, capitulum of left petasma, posterior and anterior. California Current form, $, 6.0 mm CL: g, left Mxp3 dactylus, mesial. Central form, $, 4.4 mm

CL: h, left Mxp3 dactylus, mesial. California Current form, $, 6.2 mm CL: i, thelycum,

posteroventral. Central form, $, 4.3 mm CL: /, thelycum, posteroventral.
18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 10.—Geographical distribution of records of the California Current

and Central forms of Sergestes consobrinus (line through solid circle =

literature record of the California Current form; see Milne, 1968).

3b. Central Form

FICURES 9d-f, h, j, 10, 11, 21 &

MATERIAL.-SIO, Tethys: 27(1 9), 28(1 $). SIO, Naga: 61-341

(13,2 9 $). SIO, Styx VII: 68-447(2 9 9). 68-451(23 $), 68-

468(13,19), 68-471(13, 99 9), 68-478(2 3 3 , 19). SIO, Climax II: A6<13, 19), A7<53 3 , 19), A9<23 3 . 29 9)- SIO,

FCRG 71-2: 68(13, 19)-

The material listed is deposited in the SIO Zooplankton

Collections.

DESCRIPTION.—Maxl palp vestigial and without

setae, or sometimes entirely absent (cf. S. edzvardsii,

Figure 5;).

Mxp3 dactylus (Figure 9/i) with single mesial

spines on outer margins of subsegments 1 and 2.

Outer distal spine on subsegment 1 usually reaching well beyond midpoint of subsegment 2; outer

distal spine on subsegment 2 usually reaching to or

beyond subsegment 5; outer distal spine on subsegment 4 long, usually reaching beyond midpoint

of subsegment 5. Outer terminal spine on subsegment 6 at least three-fourths as long as, sometimes

longer than, inner terminal spine.

Per3 coxa in female (Figure 9;) very similar to

that in California Current form.

Petasma (Figure 9d-f) very similar to that in

California Current form but differing in following

features: all distal lobes tending to be slenderer;

LA outer lobe with flexure occurring proximally

rather than distally and with only five to

eight hooks on anterior face; PV a mere bud, not

extending to inflection between LA and LC.

MEASUREMENTS, COUNTS, AND RATIOS

CL

x (mm)

4.1

4.8

95% cl (mm)

±0.2

±0.3

R (mm)

3.6-4.8

4.2-6.7

Total number of spines on Mxp3 dactylus inner margin

x 95% cl R

$ 33.0 ±3.7

9 36.9 ±3.1 29-41

N

15

18

N

10

10

Length of inner/length of outer terminal spines on Mxp3

dactylus

8

9

Petasma ratios

LI/CL

LT anterior/LI

LT posterior/LI

LC outer/LI

LA/LI

Md

1.02

1.01

Md

0.108

0.84

0.74

0.73

0.51

R

0.75-1.10

0.77-1.30

R

0.091-0.126

0.74-0.94

0.62-0.89

0.62-0.86

0.39-0.75

N

10

10

N

16

16

16

16

16

DISTRIBUTION.—The Central form of S. consobrinus occurs widely throughout the vast expanse of

the subtropical North Pacific (Figure 10). Unfor-
NUMBER 256 19

0.70

0.60

0.50

0.40

0.30

0.20

1 1 r

"California Current Form"

Adults O

Subadults ®

"Central Form" • O

o

o o

o

o

®

4.00 5.00 6.00

CL (mm)

FIGURE 11.—Relationship between LI length and CL in the

California Current and Central forms of Sergestes consobrinus.

tunately, this region of the Pacific is poorly represented by the collections examined, and, hence,

the range of the Central form is imprecisely known.

The area in the eastern Pacific (ca. 15°-30° N,

130°-140° W) where the two forms of S. consobrinus are most likely to co-occur and perhaps

intergrade is especially poorly sampled.

REMARKS.—A striking difference between the

California Current and Central forms of S. consobrinus is the conspicuously smaller size of the

Central variety. Judging from development of the

petasma, California Current males reach sexual

maturity when they are about the size of the largeest Central males (cf. Figure 11). It is noteworthy

that subadult California Current individuals are

quite similar to adult Central specimens in development of the Maxl palp and spination of the

Mxp3 dactylus. The possibility that these differences may be caused by differing food levels in their

respective environments must be given consideration.

Although the differences distinguishing the Central and California Current forms of S. consobrinns

closely parallel those separating S. edwardsii and

S. brevispinatus, I am not recognizing the two

forms as separate species, at least at the present

time. I have not done so because I have not had

the opportunity to examine any specimens from

the northeast Pacific where the two forms are

likely to co-occur and may intergrade. A definitive

study based on adequate material from the region

of presumed overlap may yield insight into the

relative importance of heredity and environment

in bringing about the observed differences between

the two forms and, thus, permit taxonomic treatment more satisfactory than is now possible.

4. Sergestes tantillus Burkenroad, 1940

FIGURES 7, 12, 13, 21fc

Sergestes tantillus Burkenroad, 1940:42.

Sergestes (Sergestes) tantillus.—Yaldwyn, 1957:8.

TYPE-LOCALITY.—Dana sta 3556 II (eastern tropical Pacific: 2°52'N, 82°38'W).

TYPES.—The holotype male, the only specimen

cited by Burkenroad (1940) in his description of

this species, apparently has been lost. I have deposited the following neotype in NMNH: USNM

155585, adult cf, 6.1 mm CL, sorted from a micronekton collection taken at ETP 12 sta 252 (8°25'N,

112°07'W; 17 Mar 1967; nighttime oblique tow

with BMN from ca. 200 m).

REFERENCE SPECIMENS.—I have deposited the following reference specimens in NMNH: USNM

168089: 4 adult tf tf, 5.5, 6.0, 6.1, 6.1 mm CL, and

3 adult 9 9 , 5.8, 6.0, 6.0 mm CL; sorted from same

micronekton collection as neotype.

ADDITIONAL MATERIAL.—SIO, Shellback: 13(1 $). SIO, Eastropic: 2(1 3), 4(4$$, 5$?) , 5(2$ $), 6(1 $, 1$). SIO,

Tethys: 5(1 $), 6(3$ 9), 7(34$ $), 8(21 £3 . 19). 9(2 3 3 .

29 9), H(19), 17(19), 18(1 $, 109 9), 19(203 3,4 2 9 9).

20(173 $, 429 9), 21(1^. 49 9). SIO, Styx VI: 2(23 $),

5(34$ $, 29 9). 6(33 3)- SIO, Aries I: E(13), G(22 3 3).

SWFC, ETP 12: 084(13), 106(13), 235(173 3 . 1$). 244

(3 3 3), 260(16 3 3)- SWFC, ETP 14: 199(63 3 , 19).

206(13), 213(13), 232(5 3 3), 240(2 3 3). SOSC, USARP

Eltanin 31: 67-39(13).

The material listed is deposited in the SIO Zooplankton

Collections.

DESCRIPTION.—Maxl palp relatively large, distally with one or two setae (cf. S. gibbilobatus,

Figure 2g).

Mxp3 dactylus (Figure 12d, Table 1) with single

mesial spines on outer margins of subsegments 1

and 2. Outer distal spine on subsegment 1 usually
20

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

LA

LA

PV

INDENTATION

0.7 mm

0.5 mm

b,c

FIGURE 12.—Sergestes tantillus, $, 6.3 mm CL: a, left petasma, posterior; b, c, capitulum ot

left petasma, posterior and anterior. $, 7.1 mm CL: d, left Mxp3 dactylus, mesial. 9, 6.1

mm CL: e, thelycum. posteroventral.

reaching to origin of outer distal spine on subsegment 2; outer distal spine on subsegment 2 usually

reaching to origin of distal spine on subsegment

4; outer distal spine on subsegment 4 usually reaching beyond midpoint of subsegment 5; outer terminal spine on subsegment 6 typically subequal to

inner terminal spine. Outer distal spines on subsegments 1, 2, and 4, and outer terminal spine on

subsegment 6 tending to be relatively shorter in

female.

Per3 coxa in female (Figure 12e) with short PP,

low, rounded AP, and distinct indentation at midFIGURE 13.—Geographical distribution of records of Sergestes tantillus (line

through solid circle = literature record; see Burkenroad, 1940).
NUMBER 256 21

point of dorsal lip of GC; GC extending distally

to AP.

Petasma (Figure \2a-c) with LI distinctly tapered, mesially slightly concave, bearing slight projection immediately beyond acute proximomesial

inflection. LI lobes both fingerlike; anterior lobe

shorter and stouter than posterior lobe, distally

armed with several small hooks; posterior lobe

armed with single large terminal hook. LC single,

thumblike, distally directed lobe armed with numerous hooks of varying size on posterior and distal

margins. LA single, thumblike lobe directed distally with end bent laterally and somewhat anteriorly, armed with numerous minute hooks on

upper surface. PV not reaching to inflection between LC and LA. PM with three conspicuous

lateral projections.

MEASUREMENTS, COUNTS, AND RATIOS

CL

x (mm)

5.5

6.2

95% cl (mm)

±0.1

±0.2

f spines on Mxp3 dactylus

X

55.0

56.2

95% cl

±3.9

±1.6

R (mm)

3.6-7.0

4.3-7.5

inner margin

R

50-68

53-59

N

202

83

N

10

10

Length of inner/length of outer terminal spines on Mxp3

dactylus

Md R N

$ 1.00 0.86-1.15 10

? 0.91 0.77-1.00 21

Petasma ratios

LI/CL

LT anterior/LI

LT posterior/LI

LC outer/LI

LA/LI

Md

0.091

0.69

0.79

0.96

0.43

R

0.067-0.111

0.57-0.111

0.63-1.06

0.80-1.22

0.35-0.56

N

21

11

21

21

21

DISTRIBUTION.—Sergestes tantillus is indigenous

to the eastern and central equatorial Pacific (Figure 13). Its range is obviously centered north of

the equator, with most records falling between 0°

and 20°N. It occurred most frequently in ETP

collections farthest from the Central and South

American land masses (Figure la) and, thus, appears to be more oceanic in distribution than

either S. brevispinatus or S. geminus.

5. Sergestes setnissis Burkenroad, 1940

FIGURES 14, 15, 2lb

Sergestes semissis Burkenroad, 1940:42-43.

Sergestes {Sergestes) semissis.—Yaldwyn, 1957:8.

HOLOTYPE.—Dana 3905 I, 1 tf, 4.0 mm CL (deposited in UZM).

TYPE-LOCALITY.—Dana sta 3905 I (northwestern

Indian Ocean: 4°44'N, 89°06'W); 1929.

ADDITIONAL MATERIAL.—SOSC, IIOE Anton Brunn 3: 1A

(103 c?. 15$ 9), 1B(4$3.19) , 2(1 3), SA(13 . 19), 3B(3«5 $),

4B(1 9). SOSC, IIOE Anton Brunn 6: 328A(3 $ $, 2 9 9), 328B

(5$$, 139 9), 329B(47^3 , 269 9), 330B(23<$, 29 9),

331A(2 3 $, 2 9 9), 331B(13, 2 9 9). 335A(3^ $, 19)- SOSC,

IIOE Kristna 26: 703(1 $).

All specimens other than holotype are deposited in NMNH.

DESCRIPTION.—Maxl palp relatively large, with

one or two distal setae (cf. S. gibbilobatus, Figure

2g)-

Mxp3 dactylus (Figure 14^, Table 1) with single

mesial spines on outer margins of subsegments 1

and 2. Outer distal spine on subsegment 1 usually

not reaching beyond midpoint of subsegment 2;

outer distal spine on subsegment 2 usually not

reaching much beyond juncture of subsegment 3

and 4. In male, outer terminal spine on subsegment 6 usually subequal to inner terminal spine;

in female, outer terminal spine only one-half to

three-fourths as long as inner spine.

Per3 coxa in female (Figure 14g) with broad,

blunt PP and low, rounded DP; GC not extending

to AP.

Petasma (Figure \Aa-d) with LI stout, directed

distomesially, with small projection at about midpoint of mesial margin but without strong proximomesial inflection. LT situated posteriorly to LJ;

anterior lobe cylindrical, elongate, directed distomesially, armed distally with single, large exposed

hook; posterior lobe stout, thumblike, unarmed,

directed posteriorly. LC single, thumblike, laterally directed lobe armed distally with small number of minute hooks and anteriorly with lateral

row of large hooks. LA bilobed; inner lobe with

lower margin elongate, projecting below origin of

PV, covered distally with numerous minute hooks;

outer lobe flexed back onto anterior face of inner

lobe, armed with large terminal hook and lateral
22 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

2.0 mm

f

1.0 mm

a,e

0.7 mm

0.5 mm

b-d

FIGURE 14.—Sergestes semissis, $, 5.5 mm CL: a, left petasma, posterior; b, c, capitulum of

left petasma, posterior and anterior; d, LI and LT, lateral; e, left Mxp3 dactylus, mesial; /,

$ left pleopod 2 (endopod and exopod incomplete), mesial. ?, 6.3 mm CL: g, thelycum,

posteroventral.

row of small hooks on proximoanterior margin.

PV reaching distally to or beyond inflection between LA and LC. Middle projection on PM low,

rounded.

Pleopod 2 in male (Figure 14/) with two denticles, instead of one (cf. Figure 3*,;), on midmesial

margin of propodus.

MEASUREMENTS, COUNTS, AND RATIOS

CL

x (mm)

8 5.1

$ . 6.5

95% cl (mm) R (mm)

±0.2

±0.3

3.6-6.7

4.4-7.9

Total number of spines on Mxp3 dactylus inner margin

X

$ 43.8

9 48.5

Length of inner/length

dactylus

S

?

Petasma ratios

LI/CL

LT anterior/LI

LT posterior/LI

LC outer/LI

LA/LI

95% cl

±3.3

±2.8

R

36-49

46-57

of outer terminal spines on

Md

1.00

0.74

Md

0.105

0.81

0.58

0.60

0.51

R

0.76-1.19

0.44-0.95

R

0.094-0.108

0.77-0.90

0.55-0.63

0.52-0.64

0.45-0.60

N

84

66

N

10

10

Mxp3

N

15

10

N

13

13

13

13

13

FIGURE 15.—Geographical distribution of records

of Sergestes semissis (line through solid circle =

literature record; see Burkenroad, 1940).

DISTRIBUTION.—Sergestes semissis inhabits the

northern Indian Ocean, the Arabian Sea, and the

Bay of Bengal (Figure 15).
NUMBER 256 23

6. Sergestes orientalis Hansen, 1919

FIGURES I6a-e,kj, 17, 18, 21a

Sergestes orientalis Hansen, 1919:22-26, pi. 2: fig. 2.

Sergestes (Sergestes) orientalis.—Yaldwyn, 1957:8,—Kensley,

1971:238, fig. 12.

TYPES.—Although Hansen did not designate type

specimens in his publication, individuals from

Siboga stations 148 and 230 have been labeled,

perhaps by Hansen himself, as "Types" and "Cotypes," respectively. Data on these specimens, which

were loaned to me by UZM and ITZ, respectively,

are summarized below. I have designated the male

labelled "cotype" as the lectotype.

"Types": 5cfcT, 4.0, 4.4, 5.1, 5.4, 5.4 mm CL;

3 ? $, 4.9, 5.1, 6.0 mm CL; 1 juvenile, 2.4 mm

CL; from Siboga sta 148 (0°17.6'S, 129°14.5'E);

9 Aug 1899; tow with Hensen vertical net from

1000 m to the surface; deposited in ITZ.

"Cotypes": ltf, 6.5 mm CL; 19, 6.5 mm CL;

from Siboga sta 230 (3°58'S, 128°20'E); 14 Nov

1899; tow with Hensen vertical net from 2000 m

to the surface; deposited in UZM.

ADDITIONAL MATERIAL.—SIO, Monsoon: 2(35 5 , 6$$) ,

3(12), 4(1^ , 32 9), 5(2,$3. 129$), 7(1$. 39 9). SIO,

Fazor II: Plum-28(1 $), Quince-29(2 9 9)-SIO, Styx VI: 4(4 $ ).

SIO, Circe: 15(4$$), 20(25 3 . 3 9 9) 63(1$), 80(1$), 96

(2$$), 129(2 5 3)- SIO, Scan: 41(23 3 . 7 9 9), 55(5$ $,

3 9 9)- SIO, Antipode IV: 11(3 9 9), 12(2 3 3, 2 9 9). 13(13.

19), 14(19), 15(19), 16(15, 39 9), 17(13, 59 9), 18(23 3 -

59 9), 20(23 3,4 9 9). 21(23 3 . 1 9), 22(1 3), 23(2 3 3 . 1$).

24(23 5 , 39 9), 25(2 9 9), 26(23 3 , 1$). 27(13), 28(13).

SIO, Naga: 60-215(2 2 2), 60-219a(2 3 5,3 9 2), 60-226d(15),

60-244(2 5 3), 60-248(15), 61-060(32 2), 61-065(12), 61-208

(19), 61-271(19), 61-282(19), 61-296(19), 61-299(15), 61-309

(35 5 , 59 9), 61-312(29 9), 61-316(39 9), 61-321(32 9), 61-

323(15), 61-324(35 5, 49 9), 61-326(2 2 2), 61-328(12),

61-329(25 5, 5 2 9), 61-331(5 5 5 , 13 9 9). SIO, Antipode

IX: 71-71(385 5 , 499 9). SOSC, HOE Anton Bruun 3:

3A(147-7013(1 9)), 3A(147-7016(2 5 5)), SOSC, Anton Bruun 6:

338A(7220(2 5 5)), 339A(7228<1 5 , 2 9 9)), 34OA(7238(1 5)), 340B

(7242(3 5 5)), 342B(7258(2 5 3)). 343A(7263(1 5)). UH, Blind

Faith: 6(95 3)-

Also examined were the Siboga Expedition collections (deposited in ITZ) cited by Hansen (1919) in the original description of the species. SIO and UH specimens are deposited in

the SIO Zooplankton Collections. SOSC material is deposited

in NMNH.

DESCRIPTION.—Maxl palp relatively large, with

one or two distal setae (cf. S. gibbilobatus, Figure

2g)-

Mxp3 dactylus (Figure 16A) usually with two, but

occasionally only one, mesial spines on outer margins of subsegments 1 and 2. Outer distal spines

on subsegments 1 and 2 very short, outer distal

spine on subsegment 4 minute, often little more

than seta. Inner terminal spine on subsegment 6

thicker and about twice as long as outer terminal

spine.

Per3 coxa in female (Figure 16/) with long,

broad, distally acute PP with distinct bulge on

anterior margin; AP acute; GC very broad viewed

ventrally, extending distally to AP.

Petasma (Figure I6a-e) with LI gently inflected

at proximomesial margin, distally bearing variable

number of irregular protuberances. LT with pronounced proximoposterior ledge; anterior lobe

lamellar, twisted, distally armed with large exposed

hook; posterior lobe cylindrical, elongate, distally

armed with large recessed hook. LC usually

(71% of males examined) with three, but sometimes only two, low rounded lobes armed with

numerous hooks; middle lobe largest, outer and

inner lobes about equal in size. LA bilobed; inner

lobe low, rounded, covered distally with numerous

minute hooks; outer lobe short, thumblike, directed

laterally and somewhat anteriorly, armed on anterior face with numerous hooks increasing in size

distally. PV reaching to or beyond inflection between LA inner and outer lobes. Middle projection on PM low, rounded.

CL

MEASUREMENTS, COUNTS, AND RATIOS

x (mm) 95% cl (mm) R (mm)

6.0 ±0.1 4.2-8.0

6.6 ±0.2 4.6-8.9

Total number of spines on Mxp3 dactylus inner margin

x 95% cl R

5 37.3 ±1.7 33-40

2 39.4 ±1.2 36-42

N

112

140

N

10

10

Length of inner/length of outer terminal spines on Mxp3

dactylus

Md R N

5 0.54 0.37-1.00 15

2 0.54 0.40-0.89 10

Petasma ratios

LI/CL

LT an tenor/LI

LT posterior/LI

LC outer/LI

LA/LI

Md

0.116

0.85

0.67

0.44

0.33

R

0.107-0.134

0.77-0.98

0.51-0.76

0.37-0.53

0.21-0.45

N

52

51

51

51

51
24 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

b-e,g-j

FIGURE 16.—Sergestes orientalis, $, 1A mm CL: a, left petasma, posterior; b, c, capitulum of

left petasma, posterior and anterior. 5. orientalis, $, 7.1 mm CL: d, distal LI, posterior. S.

orientalis, $ , 6.5 mm CL: e, distal LI, posterior. 5. geminus, $ , 7.7 mm CL: /, left petasma,

posterior; g, h, capitulum left petasma, posterior and anterior. 5. geminus, $ , 7.1 mm CL:

i, distal LI, posterior. 5. geminus, $, 6.9 mm CL: /', distal LI, posterior. 5. orientalis, $,

7.1 mm CL: k, left Mxp3 dactylus, mesial. 5. orientalis, ? , 7.9 mm CL: /, thelycum, posterior.
FIGURE 17.—Geographical distribution of records of Sergestes orientalis and S. geminus (line

through solid circle = literature record of S. orientalis; see Hansen, 1919, Kensley, 1971).

0.90

S. orientalis

S. geminus

"£0.80

E

0.70

OO«

o

» o

• •(30

O<X> O o

O O O

o o

o

6.00 7.00 8.00

CL (mm)

5. orientalis •

S. geminus o

.0.70

0.60

• ••• o O

00 • O O

> ao o * o

#«D «D

• • CJO O

» • OODO O O O

• • O O O

> OCD» O

O

•DO

6.00 7.00 aoo

DISTRIBUTION.—Sergestes orientalis occurs throughout the tropical Indian Ocean, the Indo-Australian

Archipelago, and the western tropical Pacific (Figure 17). The few specimens reported by Kensley

(1971) off southern Africa are probably "waifs"

advected into the region by the Agulhas Current.

A possibly isolated population of S. orientalis

occurs in the vicinity of the Hawaiian Islands.

REMARKS.—Examination of taxonomically useful

features revealed no evidence of geographic variation in S. orientalis. Samples from the Indian

Ocean, Indo-West Pacific, and Hawaiian Islands

were found by analysis of covariance not to differ

significantly (p >0.20) in length of the LI or LT

anterior lobe relative to CL. However, additional

specimens from the vicinity of the Hawaiian

Islands will have to be examined before a final

determination of that population's relationships

can be made.

7. Sergestes geminus, new species

FIGURES 2a-c, 7, 16/-;, 17, 18, 21a

HOLOTYPE.—USNM 155060, adult tf, 7.1 mm

CL.

FIGURE 18.—Sergestes orientalis and 5. geminus compared

for certain relationships: a, LI length and CL; b, LT anterior lobe length and CL.

CL ( mm)
26 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TYPE-LOCALITY.—Sorted from micronekton collection taken at ETP 14 sta 326 (4°48'N, 83°38'W);

1 Apr 1967; nighttime oblique tow with BMN from

ca. 200 m depth.

ALLOTYPE.—USNM 155061, adult $, 8.9 mm

CL; sorted from micronekton collection taken at

ETP 14 sta 037 (0°46'N, 80°42'W); 8 Feb 1967;

nighttime oblique tow with BMN from ca. 200 m

depth.

PARATYPES.—USNM 155063, 1 adult tf, 7.1 mm

CL; sorted from micronekton collection taken at

ETP 14 sta 138 (7°55'S, 88°46'W); 2 Mar 1967;

nighttime oblique tow with BMN from ca. 200 m

depth. USNM 155062, 4 adult and subadult &<$,

6.2, 6.4, 7.0, 7.3 mm CL, and 5 adult and subadult

° $, 6.8, 8.5, 8.7, 9.3, 9.4 mm CL; from same

collection as allotype.

ADDITIONAL MATERIAL.—SIO,Shellback:2(l $),6(23 3,29 9),

10(13,3? 9), 11<13,3$ $), 13(1 9)-SIO, Eastropic: 3(3 9 9).

4(63 5- 59 9), 5(43 3 , 89 9). 6(23 5 . 39 9), 8(13, 19).

9(153 3 , 189 9), 11(173 5, 19), 12(13), 13(23 5, 69 9),

14(23 5- 4 9 9), 15(5 9 9)- SIO, Tethys: 8(23 5, 69 9),

9(4 9 9). SIO, Anton Bruun 12: 65-606(13). SIO, Piquero:

29(1 3), 32(1 9), 43(2 3 5). 8-2(1 3). SIO, Quebrada: 16(2 3 5),

21(103 3). SIO, Aries I: E(13), 2(13), 3(23 5)- SWFC,

ETP 12: 059 (93 3 , 4 9 9). 067(5 3 3 , 49 9)> 075(19),

084(43 3 , 149 9), 094(23 3 , 39 9). 106(4 3 3), 142(13),

212(1 3), 224(1 9), 235(4 3 3,4 9 9), 244(1 3 , 1 9), 252(22 3 $),

260(39 9). SWFC, ETP 14: 001(29 9), 014(13), 018(113 $,

19), 022(143 3), 027(23 3), 031(33 3 , 19), 037(63 3 ,

17 9 9). 043(7 3 3). 081(13), 132(3 3 3). 138(43 3 , 19).

154(23 5. 19), 199(23 3 . 29 9). 206(13, 19), 213(43 3 ,

39 9), 232(113 5, 19), 240(93 3 , 39 9). 255(13), 263

(17 3 5). 280(15), 287(63 3 , 19). 303(23 5). 310(35 5 .

3 9 9), 326(4 3 3).

The material listed is deposited in the SIO Zooplankton

Collections.

DESCRIPTION.—Maxl palp, Mxp3 dactylus, and

thelycum as in S. orientalis (cf. Figure \6k,l)

Petasma (Figure 16/-;) very similar to that in

S. orientalis but differing in following features:

LC usually bilobed (59% of males examined),

third lateral lobe, when present, tending to be

smaller than either inner lobe; LI and LT anterior

lobe tending to be shorter relative to CL (Figure

MEASUREMENTS, COUNTS, AND RATIOS

Total number of spines on Mxp3 dactylus inner margin

x 95% cl R N

3 38.5 ±2.3 33-45 10

9 38.1 ±1.8 35-42 10

Length of inner/length of outer terminal spines on Mxp3

dactylus

Md R N

3 0.50 0.38-0.72 15

9 0.45 0.40-0.59 15

Petasma ratios

LI/CL

LT anterior/LI

LT posterior/LI

LC outer/LI

LA/LI

Md

0.108

0.86

0.68

0.43

0.33

R

0.96-0.119

0.79-0.97

0.58-0.78

0.33-0.51

0.23-0.44

N

46

46

46

46

46

CL

s

9

x (mm)

6.4

7.4

95% cl (mm)

±0.1

±0.2

R (mm)

5.0-7.7

4.9-9.8

N

239

147

DISTRIBUTION.—Like S. brevispinatus, S. geminus

is clearly indigenous to the eastern tropical Pacific

(Figure 17), differing in distribution from the former species primarily by its greater abundance

in the western part of that region (Figure la,b).

REMARKS.—Because of their close similarity in

all features, it is difficult to defend my separation

of S. geminus from S. orientalis on strictly morphological grounds. However, S. geminus and the

main population of S. orientalis appear to be separated by a large expanse of water in the central

Pacific (a hiatus occupied by S. gibbilobatus and

S. tantillus), and, thus, it does not seem likely that

there is gene flow between them. The Hawaiian

population of S. orientalis also appears to be isolated from S. geminus. Moreover, morphometric

differences in the petasmata of the two forms, although apparently minor, do indicate that they

clearly have diverged genetically. Furthermore,

there are numerous examples in other pelagic taxa

of closely related yet distinct species having disjunct distributions in the eastern and western equatorial Pacific (cf. Fleminger and Hulsemann, 1973).

Because of these parallel examples in other taxa,

as well as the morphological evidence of genetic

divergence, I prefer to recognize S. geminus as a

species distinct from S. orientalis.

ETYMOLOGY.—The name geminus ("twin" in

Latin) connotes the obvious similarities existing

between the new species and 5. orientalis.
NUMBER 256 27

8. Sergestes gibbilobatus, new species

FIGURES 2g, 4c, 7, I9a~h, 20, 21a

HOLOTYPE.—USNM 155064, adult tf, 5.6 mm

CL.

TYPE-LOCALITY.—Sorted from micronekton collection taken at Styx VI sta 3 (0°0'S, 165°42'W);

11-12 Sep 1968; nighttime oblique tow with IKMT,

2550 m maximum warp out.

ALLOTYPE.— USNM 155065, adult 9, 8.0 mm

CL; from same collection as holotype.

PARATYPES.—USNM 155066, 5 adult cftf, 5.7,

5.8, 5.9, 6.1, 6.1 mm CL, and 5 adult 9 $, 6.2,

6.3, 6.3, 7.2, 7.5 mm CL; from same collection as

holotype and allotype.

ADDITIONAL MATERIAL.—SIO, Capricorn: 41(2 $ $, 69 $).

SIO, Tethys: 11(13, 29 9), 12(1^), 14(1 ^, 19). 15(1 $),

16(1 3 , 1$), 17(4 9 9). SIO, Piquero: 29(18$ $, 29 9). 39

(2$$ , 69 9). 43(1$), 49(3$$. 29 9)- SIO, Styx VI:

2(2$ $), 3(15$ $, 249 9), 4(2$ $, 29 9). SWFC, ETP 12:

126(2$$). 134(4$$), 142(6$$), 192(4 9 9). SWFC, ETP

14: 124(1$), 128(19), 132(4$ $), 280(1$).

The material listed is deposited in the SIO Zooplankton

Collections.

DESCRIPTION.—Maxl palp (Figure 2g) relatively

large, with one or two distal setae.

Mxp3 dactylus (Figure 19g) similar in spination

to that in S. orientalis and S. geminus but tending

to have more spines on inner margin.

Per3 coxa in female (Figure \9h) similar to that

LA

1.0 mm

0.7 mm

0.5 mm

b-f

FIGURE 19.—Sergestes gibbilobatus, $, 6.9 mm CL: a, left petasma, posterior; b, c, capitulum

of left petasma, posterior and anterior. $ , 6.6 mm CL: d, distal LI, posterior. $, 7.5 mm

CL: e, distal LI, posterior. $, 7.4 mm CL: /, distal LI, posterior. $, 6.9 mm CL: g, left

Mxp3 dactylus, mesial. 9, 7.8 mm CL: h, thelycum, posteroventral.
28 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

100* 140* 180* 140* 100* 60*

FICURE 20.—Geographical distribution of records of Sergestes gibbilobatus.

in 5. orientalis and 5. geminus but lacking distinct

bulge on anterior margin of PP and having somewhat narrower GC.

Petasma (Figure 19a-/) similar to that in S. orientalis and 5. geminus but differing in following

features: LT posterior lobe with laterally directed

flexure at distal end; LC bilobed, never trilobed,

inner lobe longer than outer lobe; PV seldom

reaching to inflection between LA inner and outer

lobes.

CL

MEASUREMENTS, COUNTS, AND RATIOS

x (mm) 95% cl (mm) R (mm)

6.1 ±0.2 4.9-7.4

6.6 ±0.2 5.0-8.1

Total number of spines on Mxp3 dactylus inner margin

x 95% cl R

$ 42.5 ±2.0 39-48

9 44.3 ±2.7 40-48

N

62

57

N

10

10

Length of inner/length of outer terminal spines on Mxp3

dactylus

Md R N

S 0.56 0.43-0.80 15

$ 0.50 0.40-0.71 13

Petasma ratios

LI/CL

LT anterior/LI

LT posterior/LI

LC outer/LI

LA/LI

Md

0.120

0.86

0.72

0.44

0.30

R

0.093-0.139

0.78-0.98

0.64-0.88

0.38-0.52

0.25-0.38

N

20

20

20

20

20

DISTRIBUTION.—Sergestes gibbilobatus inhabits

the equatorial Pacific between approximately 80°W

and 170°E (Figure 20). In the western part of its

range, 5. gibbilobatus occurs in the immediate

vicinity of the equator, but to the east it appears

to be absent from equatorial waters, occurring no

farther north than 8°S in material examined. A

factor which may contribute to the apparent exclusion of S. gibbilobatus from the more equatorial portions of the eastern tropical Pacific are

the persistently low oxygen tensions characterizing

those regions (Knauss, 1963).

REMARKS.—The similarity of S. gibbilobatus to

S. geminus and 5. orientalis is obvious, the former

differing from the latter two species in only a few

features of the petasma and female genital coxa.

I found no evidence, however, of intergradation

between S. gibbilobatus and S. geminus in sectors

of the eastern tropical Pacific where the two species overlap, and, hence, I have no doubts that

5. gibbilobatus is a separate species.

ETYMOLOGY.—The specific name, from the Latin

gibbus (bent) plus lobatus (lobed), refers to the

distal flexure of the LT anterior lobe in the new

species.

Phylogenetic Relationships

Morphological separation of species of the edwardsii group is concentrated in the male copulatory apparatus, the petasma. Species differ to a

much lesser degree in development of the palp on

the first maxilla, in spination of the third maxilliped, in shape of the female genital coxa, and in

carapace length. My discrimination of relationships

within the group is based in part on conventional
TABLE 2—Character states in the edwardsii group (species are listed in parentheses after the character states they exhibit:

E = S. edwardsii; B — S. brevispinatus; CL = S. consobrinus, California Current Form; C2 = 5. consobrinus, Central Form;

T = S. tantillus; S = S. semissis; O = S. orientalis; Ge = S. geminus; Gi = S. gibbilobatus)

1. Palp on Maxl

2.

3. LI proxi

4. LT poste

6. LC

7. Lobe(s) of LC

8. LA

9. LA outer lobe

10. PV

11. I'M mesial pro

12. LI length/CL

14. LT posterior lobe length/LI

15. LC outer lobe length/LI

16. LA length/LI

20. Outer distal spine

subsequent 1 of Mx

21. Outer distal spine on

subsegment 2 of Mxp3 dactylus

22. Outer mesial spines on

subsegments 1 and 2 cf M>p3

dactylus

26. Number

27. Number spi

29. Mean CL (mm)

30. Mean CL (mm)

b. Reduced, lacking setae (E,C2)

b. Absent (E,B,C1,C2,T,S)

nflection at

b. Nearl traight (S)

a. Tapered, fingerlike (E,B,C1,C2,T)

d. Thumblike,

b. Twisted, lamellar (S,O,Ge,Gi)

a. Single lobed (T,S)

c. Usually trilobed (6)

rounded (O,Ge,Gi)

b.

a. Single lobed (T)

b. Bilobed, inner lobe projecting distally (E,B,

c. Bilobed, inner lobe projecting laterally (S)

LA (E,B,Cl,C2,T,S,O,Ge)

(E,B,C1,C2,T)

a. < 0.100 (T)

b. 0.100 - 0.120 (B,Cl,C2,S,O,Ge,Gi)

c. > 0.120 (E)

a. < 0.60 (E,S)

b. 0.61 - 0.70 (Cl,O,Ge)

c. 2 0.71 (B,C2,T,Gi)

a. < 0.50 (0,Ge,Gi)

b. 0.51 - 0.75 (E,B,C1,C2,S)

c. > 0.75 (T)

a. < 0.35 (O,Ge,Gi)

b. > 0.35 (E,B,C1,C2,T,S)

a. Extends to AP (S)

b. Does not extend to AP (E,B,C1,C2,T,O,Ge,Gi)

b. Dors,

a. Ante argin with bulge <O,Ge)

h length subsegment 2(O,Ge,Gi)

b. i length subsegment 3(E,B,C1,C2,T,S)

a. I (E,B,C1,C2,T,S)

b. 2 (O,Ge,Gi)

Prominent (E,C2,T)

a. < 0.60 (O,Ge,Gi)

b. 0.61 - 0.80 (B,C1)

c. > 0.80 (E,C2,T,S)

a. < 0.60 (Cl,O,Ge,Gi)

b. 0.61 - 0.80 (B,S)

c. > 0.80 (E,C2,T)

50 (T)

50 (T)

5,O,Ge,Gi)

;,O,Ge,Gi)

b. 2 mesial projections (S)

a. 4.0 - 4.5 (C2)

b. 4.6 - 5.4 (E,B,S)

c. 5.5 - 5.9 (Cl.T)

d. 6.0 - 6.4 (O,Ge,Gi)

a. 4.5 - 5.0 <C2)

b. 5.1 - 6.0 (E)

c. 6.0 - 7.0 <B,Cl,T,S,O,Gi)

d. 7.1 - 7.5 (Ge)
30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

considerations of petasma morphology and in part

on 30 equally weighted characters drawn from all

aforementioned features. These characters and their

expression ("character state") in different species

of the group are listed in Table 2.

To assess phenetic similarities within the edwardsii group, I used the 30 characters in calculations of an index of affinity between all possible

pairs of geographic populations. The two forms of

S. consobrinus are considered separately in this

analysis. In its present usage, the index of affinity

J

 l

is denned as — =., where C is the numC 2VC

ber of characters examined in the analysis and J

is the number of character states which are identical in the pair of populations being compared.

Values of the index greater than 0.5 have been

found empirically to provide objective groupings

of species (Fager, 1969; Fleminger and Hulsemann,

1974).

Examination ot the index of affinity matrix

(Table 3) reveals two mutually exclusive assemblages of species. Within either assemblage all values of the index exceed 0.5. One assemblage comprises S. edwardsii, S. brevispinatus, and S. consobrinus; the other comprises S. orientalis, S. geminus,

and S. gibbilobatus. Both of these assemblages (or

"lineages") are easily recognizable through subjective evaluation of diagnostic characters, particularly the petasma.

Although S. tantillus did not show high numerical affinities with every member of the S. edwardsii

assemblage (Table 3), obvious similarities in petasma structure strongly suggest that it is a member of that lineage, although apparently a diverTABLE 3.—Morphological similarity of species of the edwardsii

group, as estimated by the index of affinity (values >0.50

underlined)

\

s.

s.

s.

s.

s.

s.

s.

\

\

\

\

Specie

edvards

brevlap

consobr

Califor

Current

consobr

Central

tantill

aeniasr

orienta

ae-inus

Species

V

\

\

i i

ClTatus

inus,

n i a

Form

inus

Form 118

5

Lis

3

a

0

n

oi

0 .

0 .

0 .

0 .

0 .

0 .

0 .

24

1 1

41

2 8

19

23

a3

077T

c

1

i

VI

0.

c.

0.

0.

0

0

0

2 4

3 4

4 1

2 8

1 4

2 8

^_,

c

col

0.2 1

0 . 34

0.4 4

0.2 4

0 . 14

0.3 1

01

tn

E

•

0.4 4

0.4 8

O_J1

0 .

0.

8

11

p

H

C

oil

0.58

07T4

67T7

0.5 4

5

13

O

3

8

ui

0

c

u

0.7 1

075?

oTSs

•

i a

0

c

« o a

C -H

O C a

H h V

CJ U J3

oil in

0.5 8 0.6 8

877?

gent one. S. semissis does not show particularly

high affinities with either of the two major lineages,

and judging from certain unique features in its

petasma, male second pleopod, and female genital

coxa, it seems likely that this species represents a

third, independent lineage within the edwardsii

group.

On the basis of similarities in petasma morphology, S. edwardsii and S. brevispinatus, on the one

hand, and the two geographical forms of S. consobrinus, on the other hand, would appear to comprise distinct, although closely related, pairs of

populations within their lineage. In the numerical

analysis (Table 3), these similarities are to a large

extent obscured by the inclusion of other, less

complex features. Within the other major lineage,

comparison of petasma structure reveals that S.

orientalis and S. geminus comprise a sibling pair

distinct from S. gibbilobatus.

Although morphological separation of geographical populations within the edwardsii group is concentrated in the petasma, similarities in this structure should not be used as absolute indicators of

genealogical (i.e., "cladistic") relationships. It is

likely that interspecific differences in the petasma

serve to reproductively isolate closely related, sympatric forms. There is growing evidence that selection against the wastage of gametes in hybrid mating between related but genetically divergent species builds premating isolating mechanisms (Dobzhansky, 1970:376-382). Thus, it is significant that

closely related edwardsii species that overlap

in distribution, however slightly, (e.g., S. geminusS. gibbilobatus) tend to be much more divergent in

petasma structure than closely related pairs which

appear to be allopatric (e.g., S. geminus-S. orientalis

and 5. edwardsii - S. brevispinatus). On the basis of

available data, the Central and California Current

forms of S. consobrinus appear to be contiguous in

distribution, and, hence, appear not to conform to

the morphological-distributional pattern observed

between other closely related members of the group.

However, final judgment on this must await examination of material from the zone of potential overlap between the two forms.

To summarize, the edwardsii species group, although of monophyletic origin, appears to have

diverged early in its history into two, or possibly

three, separate lineages. Judging from interspecific

differences in petasma structure, more than one epi-
NUMBER 256 31

sode of speciation has occurred in the two major

lineages. Separation of the morphologically most

similar pairs of species within the group (i.e., S.

edwardsii - S. brevispinatus and S. orientalis - S.

geminus) would appear to be the result of the most

recent episode(s). This interpretation is, of course,

tentative, and the actual genealogical sequence of

speciation may be obscured by character divergence

(Mayr, 1970:51-53) resulting from selection against

the wastage of gametes during hybridization.

Comments on Distribution

Although the edwardsii species group is represented throughout all tropical and in certain subtropical regions of the world ocean, individual species have rather restricted ranges (Figure 2la,b): S.

edwardsii is indigenous to the tropical Atlantic; S.

orientalis and S. semissis inhabit contiguous sectors

of the tropical Indo-West-Pacific region; S. brevispinatus, S. tantillus, S. geminus, and S. gibbilobatus

occupy adjacent regions in the eastern and central

tropical Pacific; the larger form of S. consobrinus

inhabits the outer portion of the California Current

region whereas the smaller form appears to occur

throughout most of the central North Pacific.

On the basis of collections examined in this

study, the vertical distribution of the edwardsii

group cannot be described in any detail. However,

recently acquired, but incompletely analyzed, data

/

scr i»* i6c w iw izo* eo* 40*

FIGURE 21.—Probable distributions of related species of the two major lineages within the

Sergestes edwardsii group: a, S. orientalis, S. geminus, and S. gibbilobatus; b, S. edwardsii,

S. brevispinatus, S. consobrinus, and S. tantillus, also 5. semissi, a divergent species within

the edwardsii group.
32

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

from the Atlantic indicates that S. edwardsii concentrates within the upper 125 m at night but reveals little about its daytime range (Judkins, unpubl.). Similar epipelagic habits are suggested for

S. orientalis, S. brevispinatus, and S. geminus by

their frequent occurrence in extensive series of

shallow (<200 m) nighttime tows made within their

respective ranges. Furthermore, published records

(Hansen, 1919, 1922; Sund, 1920; Gurney and Lebour, 1940) suggest that, as larvae and postlarvae,

S. edwardsii and S. orientalis occur in the upper

few tens of meters, and it is probable that the early

developmental stages of other species of the group

are epipelagic, as is generally the case throughout

the genus Sergestes (Gurney and Lebour, 1940;

Omori, 1974).

If the above suppositions concerning the vertical

distribution of species of the edwardsii group are

correct, it is likely that their geographical distributions are profoundly affected by conditions in the

surface layers. A conspicuous feature of tropical

regions of the world oceans are their systems of

zonally arranged eastward and westward flowing

surface currents and near-surface undercurrents

(Knauss, 1963). The restriction of S. brevispinatus,

S. geminus, S. tantillus, and S. gibbilobatus to distinct, limited sectors of the tropical Pacific (Figure

21 a,b) is perplexing in view of the strength and

complexity of the equatorial current system in that

region (Wyrtki, 1967). These species maybe adapted

behaviorly to seek vertical strata where currents

serve to maintain them in, or return them to,

favored geographical regions. The contiguous, but

essentially nonoverlapping Indian Ocean distributions of S. orientalis and S. semissis possibly are

maintained by similar behavioral patterns in conjunction with the extensive monsoonal reversals in

circulation which typify that ocean (Taft, 1971).

However, these explanations are hypothetical and

must remain so until a fuller understanding of the

ecology and behavior of these species is achieved.

Within the edwardsii group, species appear to

exhibit relatively little overlap in their geographical

ranges (Figure 21a,6). Co-occurrences of two or

more species in the same collection were restricted

to two regions: the Indian Ocean and the eastern

tropical Pacific (Table 4). To assess the degree

of overlap within these regions co-occurrences

were analyzed by means of the index of affinity

(Fager and McGowan, 1963). In this usage, the

index is the geometric mean of the proportion

of joint occurrences corrected for sample size; i.e.,

J 1

—^^2 . ~> where A and B are the numbers

VAXB 2VB

of collections in which the two species respectively

occur, B < A, and J is the number of joint occurrences.

In only two comparisons did the index exceed

0.1 and in none did it exceed 0.5 (Table 4), a value

chosen by Fager and McGowan (1963) to signify

association in the same community. The largest

values of the index occurred between S. geminus

and S. brevispinatus (0.40) and between S. geminus

and S. tantillus (0.33). Significantly, S. geminus appears to be of a lineage distinct from that of the

two species with which it occurs most frequently.

Values of the index found between species of the

same lineage (i.e., S. geminus-S. gibbilobaus, S.

brevispinatus - S. tantillus) were low, corroborating

the subjective impression of a tendency towards

allopatry-parapatry within lineages.

TABLE 4.—Extent of overlap of co-occurring species in the

edwardsii group

Co-occurring species

Eastern tropical Pacific

S. tantillus - S. brevispinatus

5. tantillus" - S. qlbbllobatus

S. tantillus - 5. geminus

S. brevispfnatus - S. qibbilobatus

qemlnus

qibb~lloobatus

Indian Ocean

S. orientalis - S. semissis

Number of

Co-occurrences

0.07

0.03

0.33

0.01

0.40

0.07

Closely related groups of species within other

well studied pelagic taxa also tend to be allopatric

(cf. Ebeling, 1962; Ebeling and Weed, 1963; Frost

and Fleminger, 1968; Gibbs, 1969; Baird, 1971;

Fleminger, 1973; Fleminger and Hulsemann, 1974;

Johnson, 1974), supporting the idea that the prevailing mode of speciation in sexually reproducing

animals begins with genetic divergence of spatially

separated stocks (Mayr, 1970). Unfortunately, pelagic metazoans lack the fossil record necessary for

direct determination of the events leading to their

present day distribution. I am of the opinion, however, that valuable insights into the evolution and

zoogeography of these groups will result from a

better understanding of the factors determining

their present day distributions.
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