ROBERT J. MENZi

and MILTON A. MILLER

Systematics and

Zoogeography of the

Genus Synidotea

(Crustacea: Isopoda)

with an Account of

Californian Species

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SMITHSONIAN CONTRIBUTIONS TO

ZOOLOGY

NUMBER 102

Robert J. Menzies SySteiliatlCS and

and Milton A. Miller Zoogeography of the

Genus Synidotea

(Crustacea: Isopoda)

with an Account of

Californian Species

SMITHSONIAN INSTITUTION PRESS

CITY OF WASHINGTON

1972
ABSTRACT

Menzies, R. J., and M. A. Miller. Systematics and Zoogeography of the Genus

Synidotea (Crustacea: Isopoda) with an Account of Californian Species. Smithsonian Contributions to Zoology, number 102, 33 pages, 1972.—A general survey

of the systematics and distribution of the 36 species comprising the idoteid genus

Synidotea is presented, followed by a more detailed account of the eight species

represented in California. The characteristics of the Idoteinae are briefly reviewed,

and the relationship of Synidotea to the other genera in this subfamily is indicated.

Generic characters are discussed and the status of dubious species is clarified. The

geographic, thermal, and bathymetric distributions of the included species are

given. Most species of Synidotea occur in the Northern Hemisphere, predominantly

in the Arctic-Boreal regions of the North Pacific. Distributional data, combined

with paleoclimatic considerations, suggest the hypothesis that the North Pacific was

its center of origin and radiation. It is thought that the genus originated in the late

Mesozoic or early Cenozoic, when northern waters were much warmer than now,

and that ancestral populations emigrated and speciated rapidly during the glacial

Pleistocene. Lines of dispersal are postulated southward along both sides of the

Bering arc, and northward into the Arctic through the Bering Strait. S. laticauda

of San Francisco Bay is regarded as a relict descendant of an ancestral warmwater species, which also gave rise to the morphologically similar S. harfordi of

southern California and the Sea of Japan. An association between size, latitude,

and depth is indicated, with larger species occurring at higher (colder) latitudes

and greater depths. Keys, descriptions, and ecological notes are given for the eight

Californian species, including a new one from the central California coast, S. berolzheimeri.

Official publication date is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year.

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Contents

Page

Introduction 1

Acknowledgments 1

Systematic Account 1

Family Idoteidae Dana, Miers 1881 1

Subfamily Idoteinae Dana, 1852 1

Genus Synidotea Harger, 1878 2

Zoogeography 6

Geographic Distribution 6

Dispersal and Establishment 11

Thermal Distribution 11

Bathymetric Distribution 11

Systematics and Ecology of Californian Species 12

Key to Californian Species of Synidotea 13

1. Synidotea laticauda Benedict, 1897 13

2. Synidotea harfordi Benedict, 1897 16

3. Synidotea calcarea Schultz, 1966 18

4. Synidotea magnifica Menzies and Barnard, 1959 18

5. Synidotea bicuspida (Owen, 1839) 20

6. Synidotea ritteri Richardson, 1904 23

7. Synidotea pettiboneae Hatch, 1947 25

8. Synidotea berolzheimeri, new species 25

Ecology of Californian Species 28

Literature Cited 30
FIGURE 1.—Distribution of Synidotea. Note preponderance of species in Northern Hemisphere,

especially in the North Pacific.
Robert ]. Menzies

and Milton A. Miller

Systematics and

Zoogeography of the

Genus Synidotea

(Crustacea: Isopoda)

with an Account of

Californian Species

Introduction

The present paper deals in general with the systematics and distribution of the 36 species and subspecies now comprising the isopod genus Synidotea

Harger, and in particular with the eight species (including a new one herein described) that occur

along the coast of California.

A biosystematic review of this genus is needed.

The last previous attempt was made by Benedict

(1897) who published a revision of Synidotea comprising at that time 15 species. The genus has also

been treated, of course, in Miers' (1881) revision

of the family Idoteidae, to which it belongs, and in

regional monographs and checklists (notably, Richardson 1905, Hatch 1947; Gurjanova 1936, and

Schultz 1969).

The distributional picture is doubtless distorted

as a consequence of unequal collecting and reporting of these isopods from all geographic areas. Nevertheless, a synthesis of the scattered information

on the included species should lead to a better

understanding of their relationships and of factors

governing their distribution and evolution. Also, in

view of the need for up-to-date monographic accounts of most invertebrate groups on the Pacific

coast, the authors deem it desirable to include in

Robert ]. Menzies, Department of Oceanography, Florida

State University, Tallahassee, Florida, 32306, and Milton A.

Miller, Department of Zoology, University of California,

Davis, California, 95616.

this article a key to and descriptions of the Californian species of Synidotea along with ecological

notes.

Acknowledgments

The authors are grateful to the Charles P. Berolzheimer Foundation, Stockton, California, for assistance in the completion of this study. They also wish

to thank Professor Seth B. Benson, University of

California, Berkeley, for a critical review of the

manuscript.

Systematic Account

Family IDOTEIDAE Dana, Miers, 1881

Subfamily IDOTEINAE Dana, 1852

The Idoteinae, to which Synidotea and the great

majority of idoteid genera belong, differ from the

other idoteid subfamilies in that the uropods are

uniramous (except in Cleantis), the first three

pairs of pereopods are not subchelate (prehensile),

and the head is not laterally produced. The single

ramus (apical or terminal plate) of the idoteine uropod doubtlessly corresponds to the larger or ventral

plate of the biramous uropod of other valviferans,

but authorities differ as to whether this represents the

archetypal endopod or exopod. Caiman (1909) and

Racovitza and Sevastos (1910) interpret it as the

1
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 1.—Generic characters in Idoteinae.

Genera

Pleonal

sutures

complete + partial

Pereonites with

dor sally visible

epimeral sutures

Articles in

lagellum of

antenna 2

Articles in

maxillipedal

palp

Zenobiana Stebbing

Cleantis Dana

Idotea (Idotea) Fabricius

/. (Pentidotea Richardson) Menzies

Cleantiella Richardson

Engidotea Barnard

Paridotea Stebbing

Barnardidotea Menzies and Miller

Glyptidotea Stebbing

Pentias Richardson

Euidotea Collinge

Crabyzos Spence Bate

Synischia Hale

Synisoma Collinge (Stenosoma Auct.)

Colidotea Richardson

Synidotea Harger

Eusymmerus Richardson

Edotea Guerin-Meneville

Ronalea Menzies and Bowman

Erichsonella Benedict

(2-

3 + 1

3) + l

2 + 1

2 + 1

1+2

1 + 2

1+2

1+0

0 + 3

0 + 3

0 + 3

0 + 3

0 + 3

0+(2-3)

0+1

0+1

0+1

0+1

0+1

0 + 0

(1-2J-7

2-7

2- 7

2-7

2-7

2-7

5-7

0

2-7

2-7

2 7

0

0

2-7

5-7

0*

6-7

0*

5-7**

(1—2)—7***

1-3

1-3

many

many

1

many

many

many

many

many

many

many

many

few

few

many

1

1

1

1

5

4-5

4

5

5

5

5

3

5

5

4

5

5

4

4

3

4

3

4

4

*Epimera distinct only beneath pleural expansions of pereonites 2-4; none visible dorsally.

**Epimera distinct on all but pereonite 1; visible dorsally only on last three pereonites.

•**Anterolateral expansions of pleura on peronite 1 have sometimes been mistaken for epimera.

endopod, Tait (1917) thinks it is the exopod,

whereas Nordenstani (1933) believes both explanations are possible. Until further evidence (especially

from embryology and paleontology) can establish the

homologies, it would be better not to use the terms

"endopod" and "exopod" in referring to the branches

of the valviferan uropod.

The principal characteristics used in distinguishing

the 19 idoteine genera and the relationship of Synidotea to these are indicated in Table 1. It is evident

that fusion of parts—pleonites, epimera, antennal

flagellum, and maxillipedal palp—has played a prominent role in idoteid evolution. There seems to be

some linkage between pleonal and epimeral fusions

and reductions in various other parts, but there are

many instances in which the correlation breaks down.

The fact that idoteine genera can be arranged in

linear series on the basis of the degree of fusion in

one or more structures suggests the hypothesis that

they represent stages in evolution from an ancestral

idoteid which showed little or no fusion or reduction

of parts. The prototype was probably not unlike the

Oligocene fossil, Proidotea haugi Racovitza and Sevastos (1910). According to this concept, Synidotea

represents a fairly advanced stage, as it has a completely consolidated pleotelson (except for a pair of

lateral incisions), completely coalesced epimera, and

maxillipedal palp reduced to three articles. The flagellum of the second antenna, however, still shows the

generalized multiarticulate condition.

Genus Synidotea Harger, 1878

The genus Synidotea was established by Oscar Harger

(1874:374) for Idotea nodulosa Kroyer, a circumpolar species, with the following description (in

it, he later placed I. bicuspida Owen) : "Antennae

with an articulated flagellum. Epimeral sutures not

evident from above. Pleon apparently composed of

two segments, united above but separated at the sides

by short incisions. Operculum with a single apical

plate. Palpus of maxillipeds three-jointed."

Miers (1881) relegated Synidotea (along with

three other genera) to the synonymy of Edotea with
NUMBER 10 2

the statement, "The only distinction that can be

cited to separate the species of Synidotea from Edotea, viz., the long antennae with the more numerous

articulated flagellum, is, I think, scarcely of generic

importance, since the length of the flagellum is subject to considerable variation, even in different individuals of a single species." He divided Edotea

into three sections, however, one containing the two

species that Harger placed in Synidotea plus E. hirtipes (Milne-Edwards). He also described a new

variety of the latter from Japan (E. hirtipes laevidorsalis), which Benedict (1897) elevated to full

species status in the restored genus Synidotea.

Benedict (1897) divided the genus Synidotea, as

then constituted, into two new sections on the basis

of whether the pleotelson is emarginate or pointed

at the distal end. It is more or less emarginate in all

but seven species: It is pointed in S. nodulosa

(Krayer), S. spinosa spinosa Gurjanova, and S. s.

anadyrensis Gurjanova; broadly rounded in S. magnifica Menzies and Barnard and S. calcarea Schultz;

and truncate in S. pulchra Birstein and S. neglecta

Birstein. (In the latter two species, lateral teeth

bordering the truncate apical margin make it appear

somewhat excavate.) The pleotelson tapers narrowly in

S. sculpta Gurjanova and S. s. bathyalis Gurjanova,

but the author's figures indicate a slight terminal

emargination in both. The pleotelson of S. bogorovi

Gurjanova is spatulate (somewhat as in S. magnifica

and S. calcarea), but again her illustrations show a

slight emargination of the apex. Two observations

support the view that an entire, pointed apex is the

primitive condition. (1) The pleotelson of the fossil

Proidotea haugi Racovitza and Sevastos (1910) terminates thus. (2) In species having an emarginate pleotelson, the apical excavation may be absent or inconspicuous in small, immature specimens, suggesting that ontogeny recapitulates phylogeny.

There has been some confusion regarding epimeral

fusion in Synidotea. In his revision of the genus, Benedict (1897) emended the second sentence of Harger's

original diagnosis to read, "Epimeral sutures not evident above on the first four segments; on the last

three the lines of demarcation are more or less distinct." Richardson (1905) states that the epimera of

all the thoracic segments in Synidotea are ". . . perfectly and firmly united with the segments . . ." but

she also mentions the occasional presence on the last

three pereonites of ".. . a faint depression marking

the place of coalescence." The epimeral condition in

Synidotea was clarified by Sheppard (1957) who observed that the so-called epimera of the first four

somites in this genus are actually pleural expansions

of the terga, whereas those of the posterior three are

coxal in origin. She found that the coxal joints of

the first four pereopods are clearly defined and that

the outer, ringlike margin of all but the first is

marked off from the overhanging ventral surface of

the pleuron by a suture not visible in dorsal view.

The epimera of the first and posterior three pereonal

somites, however, are completely fused to their tergites. Hence, it may be stated that, in Synidotea, no

epimeral sutures are visible in dorsal view, but can

be seen from below on pereonites 2-4.

Another emendation was added by Menzies and

Miller (1956) who noted that, in Synidotea, the

genital apophyses on the midventral line of the

seventh pereonal segment of the male are fused to

form a single penis. As Sheppard (1957) shows, fusion of the paired penial processes is uncommon, but

not unique, in the Idoteidae, since it also occurs in

the closely related genus Edotea. She also points out

that a single penis is characteristic of the Astacillidae,

Pseudidotheidae, and Amesopodidae.

Thirty-six valid species have been described to

date (Table 2). Compilation of the list was difficult

because of the lack of a recent critical revision, the

scattered literature, and the many inadequate and

poorly illustrated descriptions. The task was somewhat easier for western American species, as specimens were available in our collections which helped

resolve several taxonomic tangles.

Fairly complete synonymies for the eight species

represented in California are given in the last section

which gives an account of these species. Additional

taxonomic considerations regarding several non-Californian species are given below.

Synidotea setifer Barnard, 1914, an African species,

has been transferred to another genus, Barnardidotea

Menzies and Miller, 1956, as it has one complete

pleonal suture, rather than the single incompletely

fused suture characteristic of Synidotea.

Synidotea epimerata Richardson, 1909, reported

from the Sea of Okhotsk, has been regarded as a

dubious member of the genus for two reasons. (1)

Richardson's figure of this species indicates a complete, rather than a partial, pleonal suture. This is

explained, however, by her text statement, "The abdomen is composed of a single segment with a suture

line distinct at the sides, but less distinct in the mid-
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 2.—Geographic, biogeographic (thermal) and bathymetric distribution of Synidotea.

Species

S. acuta Richardson, 1909

S. angulata Benedict, 1897

S. berolzheimeri, n. sp

S. bicuspida (Owen, 1839)

S. b. lata Gurjanova, 1933

S. bogorovi Gurjanova, 1955

S. brazhnikovi Gurjanova, 1933 ..

S. calearea Schultz, 1966

S. epimerata Richardson, 1909

S. erosa Benedict, 1897

S. excavata Gurjanova, 1933

S. fluviatilis Pillai, 1954

S. harfordi Benedict, 1897

S. hirtipes (Milne-Edwards,

1840).

S. laevidorsalis (Miers, 1881) ....

S. laticauda Benedict, 1897

S. longicirra Gurjanova, 1933 ....

S. magnifica Menzies and Barnard, 1959.

S. marplatensis Giambiagi, 1922

S. nebulosa Benedict, 1897

S. neglecta Birstein, 1963

S. nodulosa (Kroyer, 1848)

S. pacific a Nobili, 1906

S. pallida Benedict, 1897

S. pavlovskii Gurjanova, 1955

S. pettiboneae Hatch, 1947

S. pulchra Birstein, 1963

S. ritteri Richardson, 1904

Geographic Distribution

N. Pacific (Bering Sea)

N. Pacific (Washington)

N. Pacific (central California)

N. Pacific (Alaska, Bering Sea,

Washington, central California) ; Arctic; N. Atlantic

(Labrador).

N. Pacific (Sea of Japan)

N. Pacific (Sea of Okhotsk)

N. Pacific (Sea of Japan)

N. Pacific (southern California).

N. Pacific (Sea of Okhotsk)

N. Pacific (Alaska, Bering Sea)

N. Pacific (Sea of Okhotsk,

Sea of Japan).

Indian (Chilka Lake, Quilon,

Cochin).

N. Pacific (Sea of Japan; Morro Bay, Southern California;

Baja California).

Red Sea (Suez); S. Atlantic

(Cameroons, Saldhana Bay).

N. Pacific (Sea of Japan)

N. Pacific (San Francisco Bay,

California).

N. Pacific (Sea of Okhotsk) ....

N. Pacific (southern California).

S. Atlantic (Argentina)

N. Pacific (Alaska, Bering Sea,

Washington).

N. Pacific (Northwest region) .

N. Pacific (British Columbia,

Alaska, Sea of Okhotsk);

Arctic; N.Atlantic (George's

Banks, Halifax, Greenland,

Spitzbergen).

S. Pacific (Tuamotus, Mangareva?).

N. Pacific (Alaska, Bering Sea,

NW, Pacific).

N. Pacific (Sea of Okhotsk)

N. Pacific (Washington, central

California).

N. Pacific (northwest region)

N. Pacific (Vancouver Island,

B.C.; central California).

Biogeographic Region*

Arc tic (Subarctic) -Boreal

(Beringian).

Boreal (N.W. American Temperate).

Boreal (N.W. American Temperate).

Arctci-Boreal (Beringian-N.W.

American Temperate).

Boreal (E. Asiatic Temperate)

Arctic (Subarctic)

Boreal (E. Asiatic Temperate)

N. Warm Temperate (W.

American Transition).

Arctic (Subarctic)

Arctic (Subarctic)-Boreal

(Beringian).

Arctic (Subarctic)—Boreal

(E. Asiatic Temperate).

Tropical (E. Indian)

Boreal (E. Asiatic and W.

American Temperate)—N.

Warm-Temperate (W.

American Transition).

Tropical-S. Warm-Temperate

Boreal (E. Asiatic Temperate)

Boreal (W. American Temperate).

Arctic (Subarctic)

N. Warm Temperate (W.

American Transition).

Antiboreal

Arctic (Subarctic)-Boreal

(Beringian).

Arctic-Boreal

Arctic-Boreal

Tropical (S.E. Polynesian)

Arctic-Boreal

Arctic (Subarctic)

Boreal (N.W. American Temperate ).

Arctic-Boreal

Boreal (N.W. American Temperate ).

Depth

meters

86

56-79

Intertidal

29-88

5-20

2,300

5-25

813

20-80

869

7

0-10

?

9.5

1-9

30-141

55-92

Littoral

10-60

1,693

10-198

1,380; 1,641

135

Intertidal

2,887-2,917

Intertidal

Length**

mm

12

8.5-11.5

11.8

25,32

20

29

20

6

13

21

12

12.3

18

4,9,10

19, 25, 28

17.5

26

6

12.5

19,21

9.3

14,26

3

22, 8.5

12

7.5-10.5

15

12.5
NUMBER 10 2

TABLE 2.—Geographic, biogeographic (thermal) and bathymetric distribution of Synidotea—Continued.

Species

S. sculpta Gurjanova, 1955

S. s. bathyalis Gurjanova, 1955 ..

S. sphaeromiformis ManeGarzon, 1946.

S

1

. spinosa Gurjanova, 1933

S. s. anadyrensis Gurjanova,

1955.

S. tuberculata Richardson, 1909

S. variegata Collinge, 1917

S. worliensis Joshi and Bal, 1959

Geographic Distribution

N. Pacific (Sea of Okhotsk) ...

N. Pacific (Sea of Okhotsk) ...

S. Atlantic (Uruguay, Puerto

de la Paloma).

N. Pacific (Sea of Okhotsk, Sea

of Japan).

N. Pacific (Bering Sea)

N. Pacific (Sea of Okhotsk)

Indian (Gulf of Manaar, Indochina).

Indian (Bombay)

Biogeographic Region*

Arctic (Subarctic)

Arctic (Subarctic)

Antiboreal

Arctic (Subarctic)-Boreal (E.

Asiatic Temperate).

Arctic (Subarctic)

Arctic (Subarctic)

Tropical (E. Indian, Indochinese).

Tropical (E. Indian)

Depth

124-240

400

4.5

80-90

40-80

120-135

Littoral

Length**

20

16

8

16

18

16.5

7.5, 8.0

10

•Biogeographic regions adapted from Hedgpeth (1957), Sverdrup et al. (1942), and Thorne (1963).

**Measurements separated by commas are of specimens from different localities; those hyphenated indicate ranges in one

locality.

TABLE 3.—Distribution of Synidotea

A. Geographic Distribution

Oceans

Arctic

N. Pacific

S. Pacific

N. Atlantic ...

S. Atlantic

Indian

Antarctic

No. of

species

Total

2

29

1

2

3

3

0

Endemic

0

27

1

0

2

3

B. Latitudinal (Thermal) Distribution

Regions

Arctic

Arctic-Boreal

Boreal

N. Warm-Temperate

Tropical

S. Warm-Temperate

Antiboreal

Cold-Water

Warm-Water

No.

of

species

8

10

9

3

5

1

2

29

9

Length

Mean

±S.E.

(mm)

18.8 + 2.6

17.0 ±3.0

16.0±1.9

10.0

8.0 ±2.2

8.0

10.0

16.7±1.1

9.0 ±1.4

Range

(mm)

12-29

9-32

9-24

6-18

3-12

8-12

8-32

3-18

C. Bathymetric Distributiot

Depth

(m)

0-10

10-100

100-1,000

1,000-2,000

2,000-3,000

No.

of

species

9

O CO ~ CM

Length

Mean

±S.E.

(mm)

13.8 + 2.0

16.9 ±2.4

17.4 ±2.8

15.3

22

i

Range

(mm)

8-24

6-32

6-26

8.5-22

15-29

die, indicating another partly coalesced segment at

the base." (2) The figure also shows distinct epimera

on the first pereonite, and the accompanying text

states that they ". . . arise from the lateral margin

and project anteriorly beyond the place where they

are visible in dorsal view." This question has been

resolved, however, by one of our reviewers who states

that examination of specimens in the collections of

the National Museum of Natural History would show

Richardson to be in error on this point.

Synidotea excavata Gurjanova, 1933, is included

on this list of valid species, but with some hestitation

as it may be conspecific with S. epimerata. Both occur

in the Sea of Okhotsk and seem quite similar from

their descriptions, assuming the above interpretations

of the pleonal and epimeral conditions in S. epimerata are correct. Gurjanova apparently regards them

as distinct, but she may have been mislead by Richardson's figures which she reproduces in her 1936

paper. The figures, however, indicate other differences which might warrant specific separation, if

constant. For example, S. excavata seems to lack

certain tubercles on the head shown by S. epimerata,

and it has only three middorsal tubercles on the
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

pereon (pereonites 2—4), whereas 5". epimerata has a

longitudinal row of seven (one middorsally on each

pereonite). Critical morphological and ecological

comparisons of the two forms are indicated.

Synidotea laevis Benedict, 1897, and S. muricata

Benedict, 1897, we regard as junior synonyms of the

widely distributed S. nodulosa Kroyer, 1848. Hence,

these two species are not listed and their distributions are incorporated with data for the senior species

in the next section.

Synidotea marplatensis Giambiagi, 1922, a South

American species, we now consider correctly placed.

In our 1956 paper, we had suggested that it perhaps

should be put in a separate genus on the basis of

Mafie-Garzon's (1946) figures of this species. These

show a completely consolidated telson with no lateral

incisions and a maxillipedal palp of two, rather than

three, articles. Since Mane-Garzon states in the text,

however, that there is a pleonal suture line and that

the maxillipedal palp is triarticulate (as in Giambiagi's original descriptions and figures), judgment

was suspended pending clarification. We can now

confirm that Mafie-Garzon's text statements are correct, but his figures are in error on both counts.

Through the courtesy of Plinio Soares Moreira of

the Oceanographic Institute of the University of Sao

Paulo, we received specimens of S. marplatensis

which he collected at Praia Grande, south coast of

Brazil, at a depth of 16 meters. Although these isopods were taken considerably north of the previously

known range of this species (previously recorded

from Mar del Plata, Buenos Aires [type-locality] and

Rocha, Uruguay), they conform nicely to the descriptions and confirm its generic assignment.

Zoogeography

Geographic Distribution

The 36 species of the genus Synidotea are widely,

but unevenly distributed around the world (Figure 1,

Tables 2 and 3A). Of these, 33 species occur in the

Northern Hemisphere. One of these, S. hirtipes,

occurs also in the Southern Hemisphere, being found

on both sides of the equator in the Ethiopian region

(Red Sea, Cameroons, and Saldhana Bay). About

three-fourths of the known species of the genus occur

in the Northern Pacific, predominantly in the Bering,

Okhotsk, and Japanese seas. Most of these have

been described, relatively recently, by Gurjanova

(1933, 1935). By contrast, only two species (S. nodulosa and S. bicuspida) are represented in the North

Atlantic. Both of these are also found in the North

Pacific and Arctic oceans. They are probably circumpolar with southward extensions into cold-temperate

waters of both the Atlantic and Pacific.

In the Southern Hemisphere, only four species have

been reported—one in the central Pacific (S. pacifica), two along the temperate east coast of South

America (S. marplatensis and S. sphaeromiformis),

and one in South Africa (S. hirtipes), mentioned

above as the only bipolar species.

The preponderance of Arctic-Boreal species and

the paucity of species in the antipodal AntarcticAntiboreal and tropical regions are most striking. Although additional collecting will doubtless reveal additional species, it seems unlikely that future discoveries will essentially alter the present imbalance.

The poor representation in warm waters is not too

surprising since valviferans in general are scarce in

tropical and subtropical regions (Miller, 1968).

In both hemispheres, major gaps disrupt the circumglobal distribution of the genus. No species have

been reported from the presumably well-surveyed

European Atlantic and Mediterranean coasts. The

genus is not listed in the South Australian fauna

(Hale 1929), nor in the New Zealand area (Hurley

1961), nor among Chilean marine isopods (Menzies

1962).

Within the genus, one finds an interesting diversity

of distributional patterns. The records indicate a high

degree of endemicity, but some of this may be more

apparent than real, due to inadequate collections and

perhaps to incorrect determinations. Nevertheless, it

does appear that there are just a few wide-ranging

species and that the rest are relatively restricted.

The most widely distributed species are Synidotea

nodulosa and S. bicuspida whose ranges widely overlap along the western coast of Canada and Alaska

and probably along the Arctic coast of North America

(Figure 1). It should be mentioned, parenthetically,

that the distributions of these two species herein given

incorporate the localities of their synonyms. Moreover, it is assumed that their distributions are essentially continuous between reported localities. Another

far-ranging species is S. hirtipes found along the coasts

of western, southern, and northern Africa, again assuming continuous distribution between reported lo-
NUMBER 10 2

calities. It is the only species of Synidotea known from

that entire continent.

A species with restricted distribution is Synidotea

laticauda which is confined to the less saline (mesohaline and oligohaline) and warmer reaches of the

San Francisco Bay system and its freshwater tributaries (Petaluma River and near the Suisun Bay delta

of the Sacramento-San Joaquin rivers (Figure 2).

Two other estuarine or freshwater species, S. fluviatilis of India and S. mar plat ensis of South America,

also have limited distributions. There are, of course,

several marine species known from single localities,

such as S. pacifica which, when more collections are

made, probably will be found to have wider distribution than the records indicate.

An intriguing case of disjunct distribution is the

occurrence of Synidotea harfordi on both sides of the

North Pacific. Along the eastern coast, it ranges from

temperate Morro Bay, California, to warm-temperate

Baja California with long gaps between the few known

localities (Morro Bay and San Diego area, California,

and Magdalena Bay, Baja California). On the west

side of the Pacific, Gurjanova (1933) reports it from

the temperate littoral waters of the Sea of Japan.

The widely distributed S. bicuspida and S. nodulosa

also occur on both sides of the Pacific, in the Arctic,

and in the Atlantic with long gaps between reported

localities. Discontinuities, of course, may sometimes be

attributed to inadequate collecting. Hypotheses to

account for the distribution of these and other species

will be presented next.

The distributional data indicate a North Pacific

center of origin and radiation of the genus Synidotea,

as Gurjanova (1935) has already stated. Assuming

its probable establishment there in the warm environment of the Cretaceous or early Cenozoic, we might

imagine a veritable explosive evolution and dispersal

associated with paleoclimatic changes, notably the

cooling of northern waters culminating in the Pleistocene (Durham 1950, Ericson et al. 1956, Ewing and

Donn 1956, Briggs 1970). Durham presents evidence

that during the Paleocene, the 20°C. marine isotherm

along the Pacific coast, at least, was probably north

of 49° north latitude, and in the Eocene it certainly

was. Since then, he finds, it has been shifting southward, possibly with minor oscillations, until the Pliocene when it reached its present position at about 24°

north latitude. During the Pleistocene, the marine

isotherms apparently shifted intermittently northward

and southward, corresponding to glacial and interglacial epochs.

The original species in the North Pacific probably

responded to these climatic changes in various ways,

either adapting or migrating or a combination of

both. The major lines of dispersal from the North

Pacific center of origin are visualized as follows.

1. Emigrants along the west side of the Pacific

basin gave rise to present day forms in the Sea of

Okhotsk and the Sea of Japan.

2. Some ancestral populations presumably continued southward into the Indian Ocean giving rise

to the existing Indian and African species. The two

South American species may have derived from this

line. This hypothesis is supported by the similarity of

many species along the postulated migratory route

from the North Pacific center of origin southward

along the Asiatic coast, around the Malayan Peninsula to India, then westward to Africa, and around

the Cape of Good Hope to west Africa and South

America. In order of occurrence, the similar species

along this line are S. laevidorsalis and S. harfordi

(Sea of Japan), S. variegata (Indochina, Ceylon,

Chilka Lake), S. hirtipes (Africa), and S. mar platensis (South America). All of these are more or less

smooth bodied, all have the frontal margin of the

head entire (or with only a slight median excavation),

and all show an emarginate pleotelson. They are so

similar that Monod (1931) has suggested that these

forms comprise "un groupe 'hirtipes'." The other

South American species, S. sphaeromiformis MafieGarzon (1946), is somewhat similar to Monod's

hirtipes-group, being smooth bodied with an entire

frontal margin and an emarginate (slightly) pleotelson, but its broadly ovate, depressed form sets it apart.

This distinction does not preclude the possibility that

it could have evolved from the same line. Also,

Monod's inclusion of S. laticauda of San Francisco

Bay, California, in his hirtipes group is not inconsistent with our hypothesis, as will become apparent

under point 5.

3. Emigrants along the east side of the Pacific

basin gave rise to the present-day species of Synidotea

occurring along the western coast of North America

from Alaska to Baja California.

4. A few species, represented today by Synidotea

bicuspida and S. nodulosa, dispersed northward

through the Bering Strait (open since late Pliocene)

and spread both eastward and westward along the

Arctic coasts of North America and Eurasia to the

far North Atlantic and to the Barents Sea, respectively.
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

LEGEND

Synidotea laticauda

Pt. San^Qilentin

O

=

 Synidotea bicuspida

BERKELEY

AN FRANCISCO BAY

CALIFORNIA

FIGURE 2.—Distribution of Synidotea laticauda and S. bicuspida in San Francisco Bay. Note

that S. laticauda occurs mainly in the warmer, less saline parts of the bay system, probably as

a relict species (see text, page 10). S. bicuspida occupies the mouth and southern arm of the

bay, and extends northward along the Pacific coast to Alaska and circumpolar regions.
NUMBER 10 2

2. Miocene crumpling and folding.

3. Pliocene erosion and folding. 4. Pliocene mountain-making.

5. Late-Pliocene erosion. 6. Early Pleistocene faulting.

FIGURE 3.—Evolution of the central California landscape during the Cenozoic. Th e present

shoreline of the coast and San Francisco Bay is indicated by dashed lines (see also Figure 2).

(Adapted from Howard 1962.)
10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Apparently, however, they did not quite reach the

western European coast from either direction (Gurjanova, 1933b). The migration of species from the

North Pacific to the North Atlantic apparently followed the predominantly eastward trend noted by

Durham and MacNeil (1967) for other invertebrates,

notably mollusks. They attribute this largely unidirectional migration to the prevailing eastward current

pattern in the Arctic. They also suggest that the

marked dominance of Pacific emigrants may be a

function of the richer biotas of the Pacific than those

of the Atlantic. Briggs (1970) also comments on the

relatively depauperate contemporary shore faunas of

the North Atlantic and further suggests that this

ocean ". . . has provided its marine fauna a more

rigorous environment than the North Pacific," primarily, more severe temperature alterations during

the Pleistocene. The distributional data for Synidotea

supports the assumptions of these authors.

5. Some ancestral species emigrated southward

along both sides of the Bering arc, as indicated by

the occurrence of three contemporary species on both

sides of the Pacific, namely, Synidotea harfordi, S.

bicuspida, and S. nodulosa. As mentioned above, the

precursors of the latter two also dispersed northward

through the Bering Strait, thus radiating in several

directions from their presumed center of origin in the

North Pacific.

Present distributions indicate that Synidotea bicuspida and S. nodulosa are cold-water species, whereas

S. harfordi is warm-temperate. In line with our previously stated hypothesis of a North Pacific center of

origin of the genus followed by radiation and dispersal associated with paleoclimatic changes, we suggest that the ancestral S. harfordi originated when

North Pacific waters were warm and, being relatively

stenothermal, it later retreated southward along both

sides of the Bering arc before the advancing cold

water from the north. The precursors of S. bicuspida

and S. nodulosa, however, either adapted to, or originated in, the cooling North Pacific waters, and then

moved southward with the advancing cold water.

They thus followed and replaced the earlier warmwater emigrants in northern latitudes.

On the Asiatic side, the southward emigrating

populations of Synidotea harfordi reached the now

temperate Sea of Japan where their descendants exist

today. On the opposite side of the Pacific, they

eventually reached as far south as Baja California,

leaving detachments along the California coast now

represented by populations at Morro Bay and in the

San Diego region.

On the west Pacific coast, the ancestral Synidotea

bicuspida apparently reached the Sea of Japan and

evolved the subspecies S. b. lata—the only form

known and the only locality recorded for this species

along the entire Asiatic coast. On the eastern side,

it is known from several widely separated localities

from Alaska to central California.

The ancestor of Synidotea nodulosa seemingly did

not migrate as far south on either side of the Pacific

as the ancestral S. bicuspida. On the Asiatic side,

S. nodulosa is found in the Sea of Okhotsk; on the

North American side, this species is not known south

of British Columbia.

The close morphological resemblance between

Synidotea harfordi and S. laticauda and their distinctness from other Californian species clearly indicates a common ancestry despite their present geographical separation. The wide gap between their

known ranges (Table 2) can readily be explained

by extension of the preceding hypothesis regarding

S. harfordi. Let us assume that the ancestral, warmwater precursor of this species, retreating slowly

southward along the western American coast, arrived

in central California before San Francisco Bay was

formed. Populations became established in the area

and flourished in the warm coastal waters during

the successive periods of subsidence, elevation, folding, erosion, and faulting that preceded the ultimate

formation of the San Francisco Bay system in the

late Pleistocene (Figure 3). They were thus in an

advantageous position to move into it as the outside

waters became colder, and cold-water species, such

as S. bicuspida, arrived in the area. There they

adapted to the lower salinities and favorable ambient

bay temperatures and eventually evolved as S. laticauda. If speciation occurred after San Francisco

Bay was formed, which seems likely, the origin of

5*. laticauda may be dated as not earlier than the

late Pleistocene when local subsidence, coupled with

postglacial rises in sea level, inundated the common

mouth of the Sacramento and San Joaquin rivers to

form it (Howard 1962).

Meanwhile, other populations of the ancestral

Synidotea harfordi moved down to southern and Baja

California, leaving S. laticauda as a relict descendant

in San Francisco Bay. Outside, they were completely

replaced by S. bicuspida and other colder water

species now living in the area (Figures 1 and 2).
NUMBER 10 2 11

S. bicuspida occurs today along the outer coast and

in the central and southern parts of San Francisco

Bay where it overlaps slightly with S. laticauda. Because of the tidal influx through the narrow Golden

Gate and relatively minor freshwater dilution in

those parts of the bay occupied by S. bicuspida, salinities are higher and temperatures lower than in the

regions where S. laticauda is abundant (Table 5).

Dispersal and Establishment

The above-postulated dispersals doubtless occurred

slowly over long periods of geologic time. Being

benthic and lacking larvae, these isopods must depend

on transport either by natural rafts or currents or

both for dispersal over long distances. Such mechanisms leave much to chance. Founding populations

would have to be preadapted or able to adapt to

conditions of existence in the new locality which

might be quite different. Not only would the immigrants have to survive, but they would also have to

produce viable offspring in sufficient numbers to

establish and maintain the population. The presence

among the new arrivals of many females with young

in the brood pouch would favor establishment. The

availability of open ecological niches, absence or

paucity of predators, and reinforcements would also

favor colonization.

Several questions regarding the geographical distribution of Synidotea remain unanswerable in the

present state of our knowledge. How did the genus

cross the tropical barrier and reach its present loci

in the Southern Hemisphere? Some speculations as

to the origin of the two South American species and

the lone African species have been presented. But it

is difficult to conceive how the genus reached the

Tuamotus in the central Pacific where S. pacifica

occurs as the only member of the genus in the whole

South Pacific—separated by thousands of miles of

ocean from any other species of Synidotea. Future

collections, especially in the western Pacific, may help

close the gap, but until then the origin of this isolated

species must remain a mystery.

Another question is, why is it absent from the

seemingly ecologically suitable Australian, Chilean,

and European regions? Partial answers may be distance from the supposed North Pacific center of

origin and prior occupation of ecological niches in

these areas by dominant competitors and predators.

Thermal Distribution

On the point of thermal distribution, the great

majority are cold-water forms (Table 3B). Most

are rather stenothermal with 23 species found in

only one province. Twelve species occupy two provinces, but none more than two.

Although Synidotea and valviferans generally do

not conform to the rule of tropical diversity, as

exemplified by many invertebrates including other

isopods, they do fit the generalization that tropical

forms tend to be smaller than their cold-water relatives. Sive in valviferans increases poleward (analgous

to Bergmann's rule for homoiotherms), and some

frigid-zone species are remarkably large (e.g., Glyptonotus in the Antarctic and Saduria in the Arctic

region).

In Synidotea, a positive association between size

and latitude is clearly indicated, at least in the northern hemisphere (Table 3B). Mean lengths increase

progressively poleward from 8.0 ± 2.2 mm in the

five tropical species to 18.8 ± 2.6 mm in the eight

Arctic species, a highly significant difference (P

<0.01). The smallest species (S. pacifica, 3 mm) is

tropical; the largest (S. bicuspida, up to 32 mm) is

Arctic-Boreal. In the higher latitudes (Boreal to

Arctic), the differences in mean length of species in

contiguous regions are small and not statistically significant, although consistently in the expected direction. Pooled data show that cold-water species

average significantly larger than warm-water species.

In the foregoing analysis of size in relation to

latitude, depth was disregarded. It would be desirable, of course, to compare sizes of isopods in the

major latitudinal regions at the same depth intervals,

as well as sizes within each region at various depths.

Unfortunately, the data are too meager for such

critical comparisons. For example, no Arctic or

Arctic-Boreal species is recorded from shallow water

(<10 meters), and there are no depth data for

four of the five tropical species. The relationships

of size to depth, disregarding latitude, will be analyzed in the following section, and the role of

temperature will be discussed.

Bathymetric Distribution

Synidotea ranges from intertidal to depths of nearly

3,000 meters (Table 3C). Nineteen of 30 species for

which depths are recorded occur at depths of less
12 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

than 100 meters; only three have been found below

1,000 meters.

There is some indication of a relationship between

size and depth per se, but this can not be demonstrated statistically from available data. Shallow-water

species (<1 0 meters) average smaller than those of

deeper waters (Table 3C), but the difference between means of these two categories (13.7 ± 2.0 mm

and 18.1 ± 1.3 mm, respectively) is not quite statistically significant (P = 0.08). Statistical significance

could be established, however, if the four small tropical species for which no depth data are available

should prove to be shallow-water forms—a strong

possibility. Inclusion of their measurements with the

known shallow-water species would lower the mean

for this group to 12.2 ± 1.8 mm, which is significantly lower than that for the deeper water species

(P<0.02). The largest species, S. bicuspida, is recorded from 10 to 100 meters.

The reason for increased size in Synidotea with

latitude and possibly with depth is not readily apparent, but ambient temperature is probably involved. In both cases, larger mean sizes are associated

with colder temperatures. Lowered temperatures, of

course, reduce metabolic rate in poikilotherms. As

Sverdrup et al. (1942) suggest, however, this is

counterbalanced by the fact that lowered metabolism

lengthens the time required for such animals to reach

sexual maturity, thus permitting a longer growing

period with resultant larger size. They also state that

warm-water animals are relatively smaller, because

of more rapid attainment of sexual maturity and

more rapid turnover of generations. Other suggestions to account for larger size of cold-water forms

include more food and dissolved oxygen, and less

competition and predation.

The foregoing analyses of the relationship of size

to latitude, depth, and temperatures are somewhat

crude. The original data are taken mainly from the

literature which usually gives measurements of typespecimens or others which may or may not be representative, and little or no information on size variation, especially upper limits. Depth and temperature

data are frequently lacking. The distribution of most

species is imperfectly known, some being recorded

only from the type-locality. Analyses are based on

mean sizes of species, grouped rather broadly because

of paucity of data. It would be highly interesting

to compare sizes within a single wide-ranging species

such as S. bicuspida to determine whether a cline in

this character can be demonstrated in relation to

latitude and depth parameters. Finally, more studies

are needed to establish causes for the observed

relationships.

Systematics and Ecology of Californian Species

Eight species of Synidotea are represented in the

coastal waters of California: S. bicuspida (Owen),

S. harfordi Benedict, S. laticauda Benedict, S. magnifica Menzies and Barnard, S. calcarea Schultz, S.

pettiboneae Hatch, S. ritteri Richardson, and a new

one herein described. As indicated in the key given

below, these species can readily be distinguished by

the nature of the sculpturing (if any) on the dorsal

surface. Supplementary key characteristics include

the emargination (or lack of it) of the frontal margin

of the head and apex of the telson. Additional characteristics are given in the detailed descriptions which

follow the key. As noted below, some of these are

more useful than others.

The appendixes masculinae are of taxonomic value

since they show distinct differences among the species

examined as well as some similarities which help

establish relationships. For example, these stylets are

quite similar in Synidotea laticauda of San Francisco

Bay and S. harfordi of southern California (see Figures 4e and 6g). These two species also closely resemble each other and differ from the remaining six

Californian species in lacking tubercles, carinae or

other sculpturing on the dorsal body surface, and in

the absence of a median notch on the frontal margin

of the head. It will be recalled that a special hypothesis was advanced in the zoogeographical section

of this paper to account for the close morphological

resemblance of these now geographically isolated

species. Again, the appendixes masculinae of S. pettiboneae and of our new species are rather similar (see

Figures lid and I2d) and differ from those described

in other species. This similarity correlates with the

similarity of sculpturing, especially of the head, in

these two species, thus confirming their close relationship. Unfortunately, the structure of the appendix

masculina is unknown in two closely related species,

S. magnifica and S. calcarea, from southern California; their descriptions are based on female holotypes.

Among the less useful characteristics are mouthparts and the epistomal region which have been valuable in distinguishing Californian species of other
NUMBE R 10 2 13

idoteid genera, notably Idotea. For instance, the

maxillipeds in all Californian Synidotea have a single

coupling hook, except S. calcarea in which it is presumed to be absent as it is neither mentioned nor

figured in the description. Also, the frons in all

species examined lacks a protruding frontal process;

it is completely hidden in dorsal view under the

prominent postfrontal ridge or shelf, even in forms

with a median frontal notch. In the latter, however,

the protruding upper lamina of the clypeus, but not

the frons, is visible in dorsal view through the notch.

Certain other relationships may be noted. Synidotea

bicuspida is intermediate between the smooth and

the heavily sculptured forms. All Californian species

have emarginate pleons except S. magnified and S.

calcarea of southern California in which the telson

is apically rounded. These resemble S. bogorovi of

the Sea of Okhotsk in the shape of the telson.

Key to Californian Species of Synidotea

1. Body smooth. Head without preocular horns or other projections 2

Body with tuberculations, carinae or bumps. Head with preocular horns and other processes

of various size and shape 3

2. Pleotelson much less than 1/3 longer than broad (pleotelson length measured along middorsal line, width at broadest part near its anterior end). Frontal margin of head transverse or slightly concave with a slight median excavation 1. S. laticauda

Pleotelson at least 1/3 longer than broad. Frontal margin of head transverse or slightly

convex with no median emargination 2. S. harfordi

3. Apex of pleotelson broadly rounded 4

Apex of pleotelson broadly emarginate 5

4. Dorsum of head between eyes bearing 2 large, conical tubercles (larger than preocular

tubercles). Margins of head and pereon minutely serrated; posterolateral margins of

pleotelson denticulate. Eyes lightly pigmented, with few ocelli 3. S. calcarea

Dorsum of head bearing 2 small interocular tubercles (smaller than preocular tubercles).

Margins of head, pereon and pleon smooth, not serrate or denticulate. Eyes darkly pigmented, with many ocelli 4. S. magnified

5. Dorsal surface of body with transverse carinae on each pereonal somite, but without tuberculations or bumps. Preocular horns not reaching frontal border of head .... 5. S. bicuspida

Dorsal surface of body with tubercles. Preocular horns large, extending to or beyond frontal

border of head 6

6. Middorsal line of pereon generally lacking tubercles. Preocular horns project forward.

6. S. ritteri

Middorsal line of pereon with at least 1 tubercle on each somite. Preocular horns project

laterally 7

7. Lateral borders of first 4 pereonites acute. Each pereonal somite with a transverse row of

3 pointed tubercles 7. S. pettiboneae

Lateral borders of second, third, and fourth pereonites blunt. Pereonal somites beset with

small tubercles 8. S. berolzheimeri

1. Synidotea laticauda Benedict, 1897

FIGURES 4 and 5

Synidotea laticauda Benedict, 1897, pp. 393-394, fig. 4.—

Richardson 1899, p. 849; 1900, p. 228; 1905, pp. 386-

387, figs. 425-426.—Filice 1958, p. 186.—Miller 1968,

pp. 21-22, fig. 3.—Schultz 1969, p. 67, fig. 75.

DIAGNOSIS.—Cephalon. Preocular horns absent;

frontal margin concave or transverse and with slight

median excavation; eyes bulge outward, forming part

of lateral cephalic margin; tubercles or rugosities

lacking.

Pereon. Dorsal surface and lateral margins smooth,

lacking rugae, tubercles, or scales; first three pereonites with lateral margins evenly rounded, not sharply

angulate; borders of other pereonites fairly straight.

Median semilunar or crescentic patterns set off on

anterior part of tergum of pereonites 2—4, becoming

markedly narrower on posterior pereonites.

Pleon. Apex with medial terminal excavation.

Appendix masculina straight, apex bluntly pointed,

lateral margin covered with scales. Pleotelson only

slightly longer than wide.

GEOGRAPHICAL RANGE.—This species is known only

from the San Francisco Bay system, predominantly

its northern section, including Oakland Estuary, San

Pablo Bay, Carquinez Strait, Suisun Bay, and the

mouths of the Petaluma and San Joaquin rivers.
14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 4.—Synidotea laticauda: a, dorsal view of male; b, female; c, ovigerous female; d,

pleopod 1 of male; e, tip of appendix masculina; /, pleopod 2 of male; g, pereopod 1 of

male; h, pereopod 7 of male; i, uropod.
NUMBER 10 2

15

FIGURE 5.—Mouthparts of Synidotea laticauda, male: a and b, right and left mandibles,

respectively; c, maxilla 1; d, maxilla 2; e, maxilliped.

LOCALITIES.—California.

San Francisco Bay System. "Albatross" dredge

stations (Schmitt, 1921, Appendix IIA: 323-379.

See also Fig. 2) : #5720, 20 February 1912; #5721,

20 February 1912; #5766a, 8 April 1912; #5760,

23 April 1912; #5793, 7 October 1912; #5816,

3 December 1912; #5817, 3 December 1912; #5819,

10 December 1912. South San Francisco Bay: San

Francisco Buoy #1 , 29 July 1943, M. A. Miller.

Central San Francisco Bay: Crissey Field Seaplane

Station Buoy CF, 5 August 1943, M. A. Miller;

Oakland Estuary, May, June, July, and September

1941, H. W. Graham; Berkeley Yacht Harbor, 2

August 1949, E. Swan.

San Pablo Bay. San Pablo Lighted Buoy #10,

20 July 1943, M. A. Miller. Carquinez Strait: Point

Edith Buoy, 26 July 1943, M. A. Miller; Carquinez

Strait Restricted Area Buoy, 4 August 1943, M. A.

Miller. Suisun Bay: near Seal Island, 29 November

1951, F. Filice. San Joaquin River: near Pittsburg,
16 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

July 1961, A. F. Heart. Petaluma River: about 6

miles from mouth, August 1967, A. Kuris and J.

Born; 2-3 miles from mouth, 6 February 1968, W. M.

Hamner and G. Davies.

REMARKS.—The restricted distribution of this species doubtless accounts for its slight mention in the

literature and its simple synonymy.

The most distinctive features of Synidotea laticauda

are its relatively wide pleon, smooth body, and the

absence of preocular horns. In the latter two respects,

it closely resembles S. harfordi. Only its relatively

wide pleon, and the concave and medially excavated

frontal margin of its head, distinguish it from S.

harfordi. Because of the great morphological similarity between these two geographically isolated species, it has been suggested (page 10) that S. laticauda

is a relict descendant of a once widespread S. harfordi or of a common ancestral species similar to it.

As usual with quantitative characters, there is

considerable variation in relative lengths of the pleotelson and some overlapping between Synidotea harfordi and S. laticauda with respect to this character

(Table 4). Intraspecific variations are due to age and

sex with ovigerous females in general having wider

pleotelsons than males and non-ovigerous females.

Mean values for pleotelson indices (median length/

greatest width) in each of these three categories

differ greatly between the two species, however, and

the differences are highly significant, both statistically

and systematically. It should be easy to distinguish

at least between adults of Synidotea laticauda and

S. harfordi on the basis of pleotelson indexes alone,

although an occasional specimen with an intermediate

pleotelson might be difficult to identify.

2. Synidotea harfordi Benedict, 1897

FIGURE 6

Idotaea marmorata Harford, 1877, p. 117.

Synidotea harfordi Benedict, 1897, p. 402, fig. 13.—Richardson 1899, p. 849; 1905, pp. 387-388, figs. 427, 428.—

Gurjanova 1936, pp. 163-164, 266, fig. 100.—Schultz

1969, p. 67, fig. 76.

DIAGNOSIS.—Cephalon. Preocular horns absent;

frontal margin transverse or slightly convex, with no

median emargination; eyes bulge outward, forming

part of contour of lateral margin; tubercles or rugae

lacking.

Pereon. Dorsal surface and lateral margins smooth,

lacking rugae, tubercles, or scales; first three pereonites with lateral margins evenly rounded, not sharply

angulate; borders of other pereonites straight. Median

dorsal pattern on pereonites 2-4 triangulate, rather

than rounded posteriorly as in Synidotea laticauda.

Pleon. Posterior border with a median excavation.

Appendix masculina straight, apex bluntly pointed,

lateral margin scaly. Pleotelson about one-fourth

longer than its greatest width, appearing much longer

than wide.

GEOGRAPHIC RANGE.—Morro Bay, California, to

Magdalena Bay, Baja California, Mexico; Sea of

Japan.

LOCALITIES.—

California. Morro Bay, 23 January 1959, M. O.

Brown. La Jolla: 18 August 1946, gravid female from

Phyllospadix roots, R. J. Menzies and R. J. Berman;

June, 1949, 3 females among seaweed cast up into

tide pool, T. Bowman. Pacific Beach, 1 February

1943, R. J. Menzies.

TABLE 4.—Pleotelson indices (PI = length /width) in two closely related species of

Synidotea

Species

S. laticauda

No. examined

Mean PI±S.E.

Range PI

S. harfordi

No. examined

Mean PI±S.E.

Range PI

Females

Ovigerous

66

1.13±0.01

1.00-1.38

3

1.46 ±0.03

1.42-1.52

Non-ovigerous

120

1.24 + 0.01

1.05-1.43

1

2.08

Males

43

1.20±0.01

1.00-1.38

2

1.47

1.38-1.55

All

229

1.20± 0.007

1.00-1.43

6

1.57 + 0.11

1.38-2.08
NUMBER 10 2 17

FIGURE 6.—Synidotea harfordi, male: a, dorsal view; b, left mandible; c, maxilla 1; d, maxilla 2; e, maxilliped; /, pleopod 1 ; g, tip of appendix masculina; h, pleopod 2; i, pereopod 1 ;

;, pereopod 7.
18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Mexico. Cedros Island, 11 July 1953, male, intertidal, L. Berner.

REMARKS.—Harford's original description of this

species, under the name of Synidotea marmorata,

contains mainly generic characters. It is considered

applicable, however, because it is the only intertidal

species of the three species of the genus occurring in

southern California and Baja California, and the

only one of them with an incised telson. Benedict

(1897) gave the species its present name upon discovering that Harford's name was preoccupied by

S. marmorata Packard, a name now considered a

junior synonym of S. bicuspida (Owen).

Marjorie Brown's discovery (unpublished) of

Synidotea harfordi in Morro Bay, California, extends

the previously known northern limit of this species

in the eastern Pacific (formerly the San Diego Bay

region) some 300 miles northwesterly along the California coast. Her find also reduces by half the former

600-mile gap between it and its closest relative,

S. laticauda of San Francisco Bay. More significantly,

this extends the thermal distribution of S. harfordi

from the warm-temperate waters (Western American

Transition) of southern and Baja California with

their distinctive fauna (Garth 1955) into the colder

waters (West American Temperate) north of Point

Conception (34/2° north latitude, 13°C. isocryme).

This major thermal breakpoint between these two

provinces lies about 70 miles south of Morro Bay.

The discovery of S. harfordi in temperate waters of

California was not too surprising in view of Gurjanova's (1933) report of this species from equivalent

waters of the Japanese Sea (East Asiatic Temperate).

The disjunct and spotty distribution of Synidotea

harfordi on both sides of the Pacific and the long gap

between it and the closely related S. laticauda of

San Francisco Bay are explained by a hypothesis

presented in the zoogeographical section of this paper

(page 10).

3. Synidotea calcarea Schultz, 1966

FIGURE 7

Synidotea calcarea Schultz, 1966, p. 21, pi. 15; 1969, p. 68,

fig. 78.

DIAGNOSIS.—Body. Covered with fine short hairs.

Margins of head and pereonal segments minutely

serrate.

Cephalon. Preocular and anteromedial tubercles

submarginal; dorsum bearing 2 large conical tubercles

between eyes. Eyes lightly pigmented, with few ocelli.

Antenna 1 with 4 joints; antennae 2 with 5 peduncular and 6 flagellar articles. Mandible with toothed

incisor; lacinia mobilis with setal row; molar process

toothed. Endopod of maxilla 1 with 2 sensory projections. Maxillipedal palp much wider than endite;

endite with several sensory setae.

Pereon. Pereonites bear 2 or 3 dorsolateral longitudinal rugae with 2 large mediolateral tubercles.

Pereopod 1 with long unguis; dactylus and propodus

somewhat chelate. No pereopods bearing projecting

flanges on basis.

Pleon. Bluntly rounded, spatulate, with several

small teeth on posterolateral margins. Pleotelson

crossed by 3 suture lines, indicating former presence

of 4 segments; first pleonal suture continuous with

grooves in lateral margins of pleotelson. Uropods

with 2 sensory dorsolateral setal spines.

GEOGRAPHICAL RANGE AND LOCALITIES.—Known

only from type locality, Tanner Canyon, a submarine

canyon off southern California, 32°37'54" north latitude, 118°58'40" west longitude. Depth 813 m;

green mud and sand substrate.

REMARKS.—The apically rounded, spatulate pleotelson of Synidotea calcarea and S. magnifica distinguishes them from all other Californian species of

the genus which have excavated telsons. Both closely

resemble S. bogorovi Gurjanova (1955) of the

Okhotsk Sea in body shape and pattern of sculpturing. These three species show progressive reduction

in pereonal rugae with depth, possibly also with ambient temperature; S. magnifica (55-92 meters) is

much more rugose than S. calcarea (813 meters)

which is more sculptured than S. bogorovi (2,300

meters). In the Okhotsk species, the flagellum of the

second antenna has more articles (15) than that of

the Californian species (8 in S. magnifica, 6 in S.

calcarea), and its telson is more truncate than theirs.

The two Californian species can be distinguished

from each other by the characteristics given in the

key and in the above remarks.

4. Synidotea magnifica Menzies and Barnard, 1959

FIGURE 8

Synidotea magnifica Menzies and Barnard, 1959, pp. 26-27.

figs. 20, 21.—Schultz 1969, p. 69, fig. 79.
NUMBER 10 2 19

FIGURE 7.—Synidotea calcarea, female: a, dorsal view; b, maxilliped; c, pereopod 1; d, pereopod 7; e, uropod. (After Schultz, 1966)
FIGURE 8.—Synidotea magnified, female: a, dorsal view: b, first antenna; c, maxilliped; d, uropod. (After Menzies and Barnard 1959)

DIAGNOSIS.—Cephalon. Tubercle in front of eye

and anteromedial tubercles submarginal; dorsum of

head bearing a pair of smaller tubercles between

eyes; anterolateral preocular processes of head not

hornlike.

Pereon. Body segments bearing 3-4 dorsolateral

longitudinal rugae; anterior segments tuberculate.

Pereopods 2-6 bear flange on upper third of article 2.

Pleon. Apex bluntly rounded, spatulate.

GEOGRAPHICAL RANGE.—Southern California coastal

shelves: Point Conception to Oceanside.

LOCALITIES.—Menzies and Barnard (1959) report

this species from 12 stations with a depth range of

30-50 fathoms (55-91 meters).

REMARKS.—As mentioned for the preceding species, the affinities of Symidotea magnified are with another southern Californian species, S. calcarea, and a

deep-water form from the Sea of Okhotsk, S. bogorovi. All have spatulate pleotelsons.

5. Synidotea bicuspida (Owen 1839)

FIGURE 9

Idotea biscuspida Owen 1839, p. 92, pi. 27, fig. 6.—Streets

and Kingsley 1877, p. 108.

Idotaea consolidata Stimpson 1856, p. 97; 1857, p. 502.

Idotaea marmorata Packard 1867, pp. 296-297, pi. 8, fig.

6.—Whiteaves 1875, p. 262.

Idothea rugulosa Buchholz 1874, p. 285.

Idotaea pulchra Lockington 1877, p. 45.

Synidotea bicuspida.—Harger 1879, p. 160.—Sars 1885, p.

116, pi. 10, figs. 24-26.—Benedict 1897, pp. 391-392,

fig. 1.—Richardson 1899, p. 228; 1905, pp. 385-386, fig.

424; 1909, p. 110.—Hatch 1947, p. 219 ["biscuspida

Owen"].—Schultz 1969, p. 63, fig. 67.

Synidotea incisa Sars 1880, p. 433.

Edotea bicuspida.—Miers 1881, p. 66.

Synidotea marmorata.—Benedict 1897, pp. 392-393, fig.

2.—Richardson 1901, p. 542; 1905, p. 384, fig. 422.—

Ortman 1901, p. 153.—Gurjanova 1936, pp. 154-155,

267, fig. 90.—Schultz 1969, p. 64, fig. 68.

Synidotea macginitieii Maloney 1933, pp. 144-146, fig. 1.

Synidothea bicuspida.—Gurjanova 1936, pp. 152-153, 267,

fig. 88.

Synidothea bicuspida var. lata Gurjanova 1836, pp. 153—

154, 267, fig. 89.

DIAGNOSIS.—Cephalon. Prefrontal lobes small,

close to frontal margin; frontal margin usually slightly

concave, with slight median excavation; eyes swollen,

but may or may not extend beyond lateral margin;

2 minute tubercles located toward front of head near

midline.

Pereon. Covered with minute scales, particularly

evident along margins; each pereonite with a slight
NUMBER 10 2 21

FIGURE 9.—Synidotea bicuspida: a, dorsal view of young male; b, head of female; c, head of

adult male; d, head of young male; e, head of small ovigerous female; /, maxilliped; g, pereopod 7; h, appendix masculina, i, scales at apex of appendix masculina; ;', uropod. Drawings are of topotypes and homeotypes of 5. macginitiei Maloney taken 14 December, 1912 from

mud in San Francisco Bay at Albatross Station D5821 USNM 53165) which had been determined by Pearl H. Boone as S. laticauda. Maloney's species is herein assigned to the synonymy

of S. bicuspida (see page 20).
22 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

transverse ride near its posterior border; first two

pereonites with lateral margins evenly rounded, not

sharply angulate; borders of other pereonites generally

straight.

Pleon. Posterior border with median excavation.

Appendix masculina curved medially near apex which

is pointed; ventrolateral margin near apex densely

covered with spines.

GEOGRAPHICAL RANGE.—Synidotea bicuspida is a

circumpolar Arctic-Boreal-Temperate species, which

is known on the Pacific coast as far south as central

California, and on the Atlantic coast as far south as

Labrador. Gurjanova's records (1933, 1936) indicate

that it is a prominent member of the isopod fauna

of the Arctic Ocean. A subspecies, S. bicuspida lata,

occurs in the Sea of Japan.

LOCALITIES.—

Washington. San Juan Islands and vicinity: San

Juan Channel, Puget Sound, 16 July 1928, 20 meters,

K. L. Hubbs; Shoal Bay, Mud Bay, Lopez Sound,

23 July 1952, Beam Trawl, L. B. Holthuis; Friday

Harbor, 16, 31 August and 2 September 1949, J. L.

Mohr; Whidby Island, Partridge Bay, 13 meters, M.

Pettibone. Clallam County, Lapush, intertidal, 29

August 1969, M. A. Miller.

California. Sonoma County: Bodega Rock, 21

meters, summer 1968, R. Sikora; Bodega Bay, near

entrance, 9-10 meters, August 1946, July, August

1947, R. J. Menzies. Marin County: off Estero

Americano, 23 January 1948. San Francisco Bay:

"Albatross" dredge stations (Schmitt 1921, Appendix

IIA: 323-379. See also fig. 2): #5704, 1, 2 February 1912; #5705, 6 February 1912; #5711, 16 February 1912; #5712, 16 February 1912; #5724, 6 March

1912; #5727, 8 March 1912; #5731, 11 March 1912;

#5732, 11 March 1912; #5733, 11 March 1912;

#5738, 13 March 1912; #5739, 13 March 1912;

#5741, 18 March 1912; #5742, 18 March 1912;

#5745, 18 March 1912; #5767(a), 9 April, 1912;

#5776(b), 17 April 1912; #5779(a), 8 May 1912;

#5799, 29 October 1912; #5805, 30 October 1912;

#5821, 17 December 1912; #5828, 30 January 1913;

#5830, 21 March 1913.

REMARKS.—The synonymy of Synidotea bicuspida

(Owen) indicates more than the usual nomenclatural confusion so often associated with an early

described, widely distributed, variable species. Much

of the tangled taxonomy resulted from the failure of

Benedict (1897) and subsequent American authors,

notably Richardson (1905), to follow completely

Miers' (1881) synonymy of this species. Miers erred

only in placing it in the genus Edotea, from which it

was correctly removed and transferred to Synidotea

by Benedict. With this amendment and some additions, we accept Miers' synonymy in full. In the

following discussion, we shall analyze several difficult

cases and give the bases for our decisions.

Miers (1881) referred Idotaea consolidata Stimpson to the synonymy of Owen's bicuspida, but Benedict and his followers did not concur and compounded the error by applying the name consolidata

to a strikingly different species of Synidotea. Menzies

and Miller (1954) assigned Benedict's misidentified

form to S. pettiboneae Hatch, 1947 (see later discussion of that species). In our opinion, Miers was

correct in his interpretation of Stimpson's consolidata

for the following reasons:

1. Stimpson (1857: 503) described in his specimens, "a sharp, slightly elevated transverse ridge

across the thorax on each segment near its posterior

margin." These ridges are characteristic of S. bicuspida, which otherwise has an unsculptured pereon.

2. Stimpson did not mention the transverse row

of three prominent tubercles on each pereonal tergite

which Benedict, Richardson, and others describe in

their version of consolidata and which are characteristic of S. pettiboneae. Stimpson surely would have

noted these conspicuous tubercles had they been present on his specimens.

3. Distributional and locality data, though not conclusive alone, reinforce the morphological evidence

that the consolidata of Stimpson and that of Benedict

and his followers are distinct species, now recognized

as S. bicuspida and S. pettiboneae, respectively.

Stimpson's description was based on specimens taken

from sandy bottom at 10 fathoms (about 18 meters)

near the entrance of San Francisco Bay, where S.

bicuspida has often been found (Figure 2). The

specimens presumed by Benedict to belong to Stimpson's species were taken about 100 miles southward

at Pacific Grove, bottom and depth unspecified.

There is no record of S. pettiboneae in San Francisco Bay or its entrance, although it does occur both

north and south of that area, usually on outer coastal

reefs.

Benedict (1897) and his followers, including

Richardson (1905), also did not recognize Miers'

referral of Idotea marmorata Packard to Owen's
NUMBER 10 2 23

bicuspida, but maintained it as a distinct species of

Synidotea. Descriptions and figures given by Benedict

(1897: 391-392), however, indicate that the distinction is based on body proportions, marmorata being

smaller and slightly narrower with thinner epimera

than bicuspida and having relatively longer and

more slender antennal joints. Such differences among

isopods are suspect as criteria for distinguishing species; size and shape often vary with age, sex, and

breeding condition (ovigerous females are usually

wider than non-gravid females and males). Small or

unrepresentative samples may lead to erroneous conclusions. Unless found statistically significant or

clearly correlated with other characters, slight differences in bodily proportions or size should not be

used for taxonomic distinctions. Since marmorata is

only found in the North Atlantic whereas bicuspida

occurs in the Pacific and Arctic oceans, it might be

argued that the above-mentioned differences are associated with their distribution. In support of this

argument is the fact that Gurjanova's (1936) variety

or subspecies, S. bicuspida lata, is broader than the

species proper and that it is isolated from the latter

in the Sea of Japan. In this instance, however, there

are also other morphological differences so that some

taxonomic distinction is warranted, whereas no other

differences are indicated in the case of marmorata.

Hence, we accept Miers' disposition of marmorata

as a synonym of bicuspida.

Maloney (1933) distinguished his Synidotea macginitiei from S. bicuspida (Owen) on variable characteristics, especially the number of apical setae on

the maxillae. This character shows considerable developmental variation. Examination of specimens

identified by Maloney indicates that they are probably identical with S. bicuspida. If so, Monterey Bay,

where Maloney's specimens were taken, is the only

record of S. bicuspida south of San Francisco Bay

and its southern limit.

6. Synidotea ritteri Richardson, 1904

FIGURE 10

Synidotea ritteri Richardson, 1904, pp. 219-220, figs. 99a,

100, 101a; 1905, pp. 377-378, figs. 409-410.—Hatch

1947, p. 220, pi. 8, fig. 98.—Menzies and Miller 1954,

pp. 144, 154.—Schultz 1969, p. 64, fig. 69.

DIAGNOSIS.—Cephalon. Preocular horns large,

projecting well beyond frontal margin; frontal border

markedly excavate medially; eyes bulging, forming

part of lateral contour; a pair of large spiniform

tubercles anterior and medial to eyes; behind these

is another pair of swollen tubercles.

Pereon. Dorsolateral surfaces of each somite with

2-4 rugosities in a transverse row; first two pereonites

with lateral borders evenly rounded, not sharply

angulate; borders of others straight.

Pleon. Posterior border with median excavation.

Appendix masculina straight and pointed near apex

which bears 2 setae, spines or scales lacking. Pleotelson slightly wider than long.

GEOGRAPHICAL RANGE.—Cox Bay, Vancouver Island, British Columbia, to Lands End, San Francisco,

California.

LOCALITIES.—

British Columbia. Vancouver Island, Cox Bay,

15, 16 October 1970, M. A. Miller.

Oregon. Coos County, Coos Head, intertidal,

1940, G. M. Shearer.

California. Sonoma County: Goat Rock, 23 September 1968, J. Bodle; Shell Beach, intertidal, 10

July 1967, M. A. Miller; Schoolhouse Beach, intertidal, 24 September 1968, J. and J. Bodle; Bodega

Head, 8 August 1967, J. Brill. Marin County: Dillon

Beach, January 1935, O. Hartman; 15 May 1947,

M. Barr; on algae, bryozoans, and hydroids (especially Aglaophenia), 1946-1947, R. J. Menzies; 26

October 1954, M. A. Miller and J. Downey.

REMARKS.—Richardson's (1904) original description of Synidotea ritteri was sufficiently lucid to permit its subsequent recognition, and no taxonomic

complications have been encountered. Its most distinctive features are the highly developed, forward

and upward projecting preocular horns and the dorsolateral pereonal rugosities. Generally, middorsal

tubercles are lacking on the pereon, but some specimens show a low tubercle on the middorsal line,

particularly on the anterior four pleonites. Richardson does not mention any sculpturing on the pereon.

The apex of the appendix masculina is exceptionally

simple, unlike that of the other Californian species.

This species resembles Synidotea pettiboneae and

S. berolzheimeri, especially in the sculpturing on the

head.

7. Synidotea pettiboneae Hatch, 1947

FIGURE 11

Synidotea conW«"rfa/a.--Benedict, 1897, p. 393, fig. 3.—

Richardson 1899, p. 848; 1900, p. 227; 1905, pp. 383-
24 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FICURE 10.—Synidotea ritteri, male: a, dorsal view; b, anterior part of head; c, maxilliped;

d, pereopod 1; e, pereopod 7: /, appendix masculina; g, uropod; h, setae at apex of uropodal

sympod.
NUMBER 10 2 25

384, figs. 420, 421.—Hatch 1947, p. 219.—Menzies and

Miller 1954, pp. 144, 154.—Schultz 1969, pp. 65-66,

fig. 72.

Synidotea pettiboneae Hatch, 1947, p. 221, pi. 14, figs. 168,

169.—Menzies and Miller 1954, p. 154.—Schultz 1969,

p. 65, fig. 70.

DIAGNOSIS.—Cephalon. Preocular horns large but

directed laterally, rather than frontally (as in S.

ritteri), and accordingly extend only slightly beyond

frontal margin; frontal border slightly excavate between preocular horns; eyes bulging and extending

outward as part of lateral contour; 2 large spiniform

tubercles in front of, and medial to, eyes; behind

these is another pair of more swollen tubercles.

Pereon. Dorsolateral surface of each pereonite

with a transverse row of 3 sharp tubercles; pereonites

1-3 with lateral margins sharply angulate; borders of

others become progressively less angulate posteriorly.

Pleon. Posterior border with median excavation.

Appendix masculina flattened and expanded near

apex, with lateral and medial borders near expanded

areas serrated, apex pointed. Pleotelson slightly wider

than long.

GEOGRAPHICAL RANGE.—Neah Bay, Washington to

Pillar Point, San Mateo County, California.

LOCALITIES.—

Washington. Clallam County: Neah Bay, 27-55

meters, 6 July 1940, M. Pettibone (University of

Washington collections of M. Hatch) ; Lapush, intertidal, 29 August 1969, M. A. Miller.

California. Sonoma County, Shell Beach, 14 August 1968, J. Bodle. Marin County: Dillon Beach,

intertidal with hydroids and bryozoans, October 1947,

R. J. Menzies; 0.5-1.0 mile west of Dillon Beach,

9-10 meters, 11 July 1947, R. J. Menzies; intertidal

on Aglaophenia (with our later described new species), 12 June 1941, G. M. Schreiber. San Mateo

County, Pillar Point, intertidal, 4 June 1939, W. M.

Marshal. Monterey County, Pacific Grove (Benedict

1897).

REMARKS.—It seems apparent from the original

description of S. consolidata that Stimpson (1856,

1857) was referring to the species Synidotea bicuspida

(Owen) and not to the species which Benedict and

Richardson called his S. consolidata. This left Benedict's and Richardson's S. consolidata without a

name. Hatch (1947) described S. pettiboneae as a

new species which he thought was related to the

S. consolidata (of Richardson 1905, not Stimpson).

and examination of his specimens shows them indeed

to be identical with that species. Accordingly, Hatch's

name for the species becomes available. In view of

Stimpson's original description, it is difficult to comprehend Benedict's and Richardson's assignment of

their S. consolidata to Stimpson's S. consolidata because these two species now known as S. pettiboneae

and S. bicuspida, respectively, are strikingly different

species. Curiously, Miers (1881: 66) equated Stimpson's S. consolidata with S. bicuspida (Owen) but his

work was not followed, although it was cited, by

both Benedict and Richardson.

The pointed bumps on the body and head of

Synidotea pettiboneae consitute its most diagnostic

feature. In the strong development of preocular

horns, this species is like S. ritteri except that those

of the latter curve inward, whereas those of S. pettiboneae project outward.

8. Synidotea berolzheimeri, new species

FIGURE 12

DIAGNOSIS.—Cephalon. Preocular horns large, directed laterally and extending only slightly beyond

frontal margin; frontal border slightly excavate between preocular horns; eyes bulging and forming

part of lateral contour; a pair of small tubercles just

behind frontal notch, a pair of minute tubercles

between eyes, and a transverse row of three minute

tubercles behind occipital groove.

Pereon. First pereonite with angulate lateral borders: sides of following somites slightly convex or

straight, with little or no intersegmental incisions.

Each tergite bears a low median tubercle and several

minute lateral tubercles.

Pleon. Telson with median terminal excavation.

Anterior end bears a few inconspicuous median and

lateral tubercles. Appendix masculina (Figure \2d)

with expanded, flattened shoulder; outer, but not

inner, border spinulate at shoulder; distal third beyond shoulder narrow, medially bent and apically

pointed. Pleotelson slightly wider than long.

Measurements. Holotype male: length 11.8 mm.,

width (at third pereonal somite) 4.5 mm. Allotype

ovigerous female: length 7.6 mm., width 3.5 mm.

GEOGRAPHICAL RANGE.—Central California from

Morro Bay, San Luis Obispo County, to Shell Beach,

Sonoma County.

LOCALITIES.—California. Marin County—Dillon
26 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 11.—Synidotea pettiboneae, male: a, dorsal view; b, maxilliped; c, pereopod 7; d, pleopod 2; e, uropod; /, setae at apex of uropodal sympod.
NUMBER 10 2 27

FIGURE 12.—Synidotea berolzheimeri, new species, male: a, dorsal view; b, maxilliped; c, pereopod 7; d, appendix masculina.
28 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Beach (type-locality) : On hydroid Aglaophenia, 21

February 1948, R. J. Menzies; on Aglaophenia, July

1935, O. Hartman; on Aglaophenia, 12 June 1941,

G. M. Schreiber; 20 July 1948, V. Schomberg; 31

October 1958, M. A. Miller; July 1960, B. Neal.—

Tomales Point, on Aglaophenia, June 1941, R. J.

Menzies.—Off Estero Americano, 23 January 1948,

R. J. Menzies. Sonoma County, Shell Beach, 14 August 1968, J. Bodle. San Luis Obispo County, Morro

Bay, 23 January 1958, M. O. Brown.

DISPOSITION OF MATERIAL.—Types are deposited

in the United States National Museum, catalog numbers: holotype o" 134489, allotype $134490, paratypes 134491. Other material is in the authors' collections.

REMARKS.—This species is named for Mr. Charles

P. Berolzheimer of Stockton, California, in appreciation of his enthusiasm in the development of the

Pacific Marine Station of the University of the Pacific

at Dillon Beach, Marin County, California, near

which this species was first collected, and of his interest in this study.

Synidotea berolzheimeri more closely resembles S.

pettiboneae than any other Californian species. Both

are tuberculate dorsally with a median row of tubercles, but those of the former are minute compared

to the spine-like tubercles of the latter, and the

lateral ones are differently arranged.

The constant association of our new species with

Aglaophenia indicates that it preys on that hydroid.

The rather long gap between the southern limit

of Synidotea berolzheimeri at Morro Bay, California,

and the next known locality to the north (Tomales

Point, Marin County) will probably be filled in by

future collections along the intervening coast.

Ecology of Californian Species

The following ecological notes summarize what

little is known concerning the relationships of Californian species of Synidotea to their environment.

Most of our knowledge is perforce inferred from

rather scanty collection data. Clearly, many aspects of

their ecology remain to be investigated.

Distributional data indicate that temperature plays

an important role in the ecology of most species of

Synidotea. Of the eight Californian species, five

occur north of Point Conception (34^2° north latitude) and two south of it, and one (S. harfordi) on

both sides of it. Point Conception is a major thermal

breakpoint which separates the warm-temperate waters off the southern California coast from the colder

temperate waters of the central and northern part

of the state. The southern group comprises S. harfordi, S. magnifica and S. calcarea; the northern contingent includes S. pettiboneae, S. ritteri, S. berolzheimeri, S. bicuspida, and S. laticauda. S. harfordi

might also be included in the northern group, but

it is predominantly a southern California species.

All species are benthic. Four of them, Synidotea

harfordi, S. berolzheimeri, S. pettiboneae and S. ritteri typically inhabit the lower intertidal zone of

wave-swept rocky coasts. Specimens of the latter two,

however, have also been taken subtidally at depths

of a few fathoms, and it is likely that the other intertidal species may also extend into subtidal regions.

In southern California, S. magnifica lives on the subtidal shelf, whereas its close relative, S. calcarea, inhabits submarine canyons. The typically subtidal

species of northern California are the wide ranging

S. bicuspida and the restricted S. laticauda.

Both Synidotea bicuspida and S. laticauda occur in

the San Francisco Bay system, but are geographically

and ecologically segregated there, as well as morphologically distinct. S. bicuspida is widely distributed along the coast of North America from Monterey Bay, California, to Point Barrow, Alaska, and

elsewhere in Arctic-Boreal areas. In San Francisco

Bay, it occurs only in the colder, more saline sections

around the mouth and in the central and southern

sections. It is replaced in the warmer, less saline

northern part of the bay system by S. laticauda which

also ranges into oligohaline Suisun Bay, the Petaluma

River, and near the delta of the Sacramento-San

Joaquin rivers. There is apparently some overlap in

the distribution of these species as S. laticauda has

recently been reported in both the southern and

central sections of the bay (Miller 1968).

It is difficult to say which factor or combination

of factors is responsible for the segregation of Synidotea bicuspida and S. laticauda in San Francisco

Bay. Salinities to which the latter are exposed are

lower and more variable than those encountered by

the former. For bay localities where S. bicuspida has

been found, they range between 30—31 %o (near the

Golden Gate) to 27-29 %0 in the middle and southern division. For S. laticauda, they scale down from

these values to 25 %o (south San Pablo Bay), 10—16

%o (Carquinez Strait), and 0.3—1.0 %o (near the

Sacramento-San Joaquin delta) (Miller et al., 1928;
NUMBER 102 29

TABLE 5.—Physical factors in the environment of two species of Synidotea occurring

in San Francisco Bay and vicinity. (Data based on Albatross investigations in 1912.)

Species

S. laticauda

S. bicuspida

Annual Mean

Salinity (%)

Average

18.57

30.34

Range

15.24-29.14

26.97-34.00

Temperature (°C.)

Average

12.99

12.12

Range

12.44-13.29

10.00-13.53

Bottom

soft-mudgravel

soft mudhard,

clean,

gray sand

Depth

(meters)

1.8-110

3.8-26

Filice 1954. See also Table 5). The lower salinities

in the upper reaches of the bay, where S. laticauda

abounds, are due to dilution by fresh water from the

large Sacramento and San Joaquin rivers and lesser

Napa and Petaluma rivers which empty into the

northern arm of the bay system. Bay salinities fluctuate diurnally with the tides, and seasonally with the

annual rainfall cycle which features a rainy winter

and early spring and a prolonged dry season during

the summer and fall when runoff is greatly reduced.

Fluctuations are less in the southern arm of the bay

system which has no large freshwater tributaries.

Within recent years, several large dams have been

built across the major tributaries to the California

central valley drainage and more are planned to

control floods and equalize runoff. This should greatly

decrease the amplitude of seasonal salinity fluctuations, at least in the upper reaches of the bay. What

effect these changes will have on the bay biota and

particularly on populations of 5*. laticauda remains

to be seen.

Temperatures are lower outside and at the mouth

of San Francisco Bay, where Synidotea bicuspida

occurs, than in the inner parts to which S. laticauda

is adapted. Miller et al. (1928) report that the

lowest average temperature in 1923 was 14.1°C.

at Fort Point near the entrance to the bay, with

increases to 17.8°C. at the middle of the bay (Oakland), to 20.6°C. at Dumbarton Bridge in the southern part, and to 19.1 °C. at Carquinez Strait at the

northern end (see also Table 5).

Other factors that may be involved in the segregation of Synidotea bicuspida and S. laticauda are

turbidity, dissolved oxygen, and substrate. Turbidityis relatively high at the two ends of the bay, especially

at the northern end owing to silt from the large

rivers. Toward its mouth, the water becomes clearer

with negligible turbidity at the Golden Gate. Oxygen

content is higher in the colder, less polluted water

at the bay entrance than in the upper reaches where

it is almost invariably below saturation. The bottom

inhabited by both species was not greatly different

though S. laticauda was found most often where the

bottom was muddy, whereas S. bicuspida was more

frequently taken from a sandy bottom (Table 5).

The latter species was taken from a mud bottom

often enough (22 percent of the stations), however,

to rule out the possibility that bottom texture alone

exerts a strong influence on its distribution.

From the foregoing comparison of distribution and

habitat of the two species of Synidotea occurring in

the San Francisco Bay system, we conclude that S.

laticauda is better able to tolerate low salinities and

salinity fluctuations, higher temperatures, turbidity,

and other estuarine conditions than S. bicuspida.

The latter is confined to those parts of the bay which

are more oceanic with respect to the factors mentioned. It appears to be a predominantly cold-water,

open coast form which may have been carried into

the bay by strong tidal currents and has established

populations in the more oceanic parts of it. S. laticauda, on the other hand, is regarded as an estuarine

species, with greatest abundance in the upper, mesoand oligohaline reaches of the bay. Strong currents,

especially at ebb tide, could transport it seaward and

thus account for its occurrence near the mouth of the

bay, the seaward limit of its distribution. The overlap

of S. laticauda and S. bicuspida in the central and
30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

southern parts of the bay indicates that conditions

there represent limits of tolerance for both and thus

constitute a physiological barrier to the distribution

of each. Whether the limiting factors operate on

survival of adults or young, reproduction, or indirectly through food supply is a question that might

be resolved by experiment.

The food, predators, and other biotic relationships

of the Californian species of Synidotea have not been

adequately studied. The frequent association of S.

pettiboneae and S. berokheimeri with the hydroid

Aglaophenia indicates that they feed on it. S. laticauda doubtless feeds upon the gymnoblastic hydroid,

Bimeria franciscana Torrey in San Francisco Bay

(Miller 1968). The association of many species with

bryozoans also leads one to suspect that these are a

common source of food.

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