Revision of the threadfin genus Polydactylus (Perciformes:
Polynemidae) from the eastern Pacific Ocean
Hiroyuki Motomura1*, Seishi Kimura2, and Yukio Iwatsuki3
1
Fish Division, Department of Zoology, National Science Museum (Natural History), 3-23-1 Hyakunin-cho, Shinjuku-ku, Tokyo
169-0073, Japan (e-mail: motomura@kahaku.go.jp)
2
Fisheries Research Laboratory, Mie University, P.O. Box 11, Wagu, Shima, Mie 517-0703, Japan(e-mail: kimura-s@bio.mie-u.ac.jp)
3
Division of Fisheries Sciences, Faculty of Agriculture, Miyazaki University, 1-1 Gakuen-kibanadai-nishi, Miyazaki 889-2192,
Japan (e-mail: yuk@cc.miyazaki-u.ac.jp)

Received: March 7, 2002 / Revised: July 5, 2002 / Accepted: July 10, 2002

IchthyologicalResearch©The Ichthyological Society of Japan 2002

Ichthyol Res (2002) 49: 358–366

Abstract The taxonomy of the eastern Pacific species of Polydactylus was revised, resulting in therecognition of two species: Polydactylus approximans (Lay and Bennett, 1839), a senior synonym of
Polynemus californiensis Thominot, 1886; and Polydactylus opercularis (Gill, 1863), a senior synonymof Polynemus melanopoma Günther, 1864. Redescriptions of the two species and comparisons withrelated congeners are presented. The type material status of Polydactylus approximans and the type
locality of Polydactylus opercularis are also discussed.
Key words Revision · Polydactylus approximans · Polydactylus opercularis · Eastern PacificF

our nominal species of the family Polynemidae, viz.,
Polynemus approximans Lay and Bennett, 1839,
Trichidion opercularis Gill, 1863, Polynemus melanopoma
Günther, 1864, and Polynemus californiensis Thominot,
1886, have been reported from the eastern Pacific Ocean. Of
these, Polynemus approximans and Trichidion opercularis
have been widely regarded as valid species, both having
been regarded to belong to Polydactylus (Eschmeyer andHerald, 1983; Allen and Robertson, 1994; Schneider, 1995).
Although these two species have been mentioned in numerous brief treatments of general classification and regional
faunal studies (Hildebrand, 1946; Bussing and López S.,
1994; Grove and Lavenberg, 1997; Chirichigno F. and Vélez
D., 1998), they have at no time been reconsidered on thebasis of type data and an appropriate range of nontype material. Furthermore, two other nominal species,
Polynemus californiensis and Polynemus melanopoma,
have not been reported since their original descriptions,
except in a type catalog report of the former, resulting in thetaxonomic status of the two species still not being clear.
Polynemus californiensis and Polynemus melanopoma
are herein regarded as junior synonyms of Polydactylus
approximans and Polydactylus opercularis, respectively,
following examination of type and non-type material, representing wide distributional ranges. Redescriptions of thelatter two are given here, along with a discussion of certain
aspects of the type data of both.

Materials and Methods
Counts and measurements follow Hubbs and Lagler (1947)
and Motomura et al. (2000b, 2002a). Counts of pectoral

filaments begin with the anteriormost (ventralmost) element. Standard and total lengths are expressed as SL and
TL, respectively. Terminology of the supraneural bones follows Mabee (1988), and the formula for configuration of thesupraneural bones, anterior neural spines, and anterior dorsal fin pterygiophores follows Ahlstrom et al. (1976). Institutional codes follow Leviton et al. (1985). The presence of aswimbladder in Polydactylus approximans and its absencein Polydactylus opercularis were confirmed from sevenspecimens [USNM 15129, 41393, 46488 (1 of 3 specimens),
46876, 47464, 65621, and 94015] and 15 specimens [USNM
50343 (2), 65622 (3), 79871, 177799 (1 of 2), 181287 (5),181320, 200371, 367309 (1 of 18)], respectively, the abdomens of these fish having already been dissected. Osteological characters were confirmed from X-ray photos taken of
11 Polydactylus approximans [USNM 43265, 53517, 65621,
127892, 220698, 220779, 220784 (3); BMNH 1863.12.16.30,
1866.1.14.6] and 10 Polydactylus opercularis [USNM 177799(2), 181287 (5), 367308 (2); BMNH 1864.1.26.321].

Genus Polydactylus Lacepède, 1803
Polydactylus plumierii, described as a new genus and species
by Lacepède (1803), is presently regarded as a junior synonym of a western Atlantic species, Polydactylus virginicus(Linnaeus). Accordingly, the type species of Polydactylus isconsidered to be the same species as Polydactylus virginicus(Talwar and Jhingran, 1992; Castro-Aguirre et al., 1999).
Polydactylus differs from seven other valid polynemid
genera (listed by Motomura and Iwatsuki, 2001a) in having
the following combination of characters (Motomura et al.,2000a,b, 2001a,c,d,g,j, 2002b; Motomura and Iwatsuki,

Revision of eastern Pacific Polydactylus359

2001b): dermal eye opening 1.3 or less in snout length (1.3
or more in Parapolynemus and Polynemus, see Feltes, 1993;
Motomura and Sabaj, 2002; Motomura et al., 2002c); widthof tooth band on upper and lower jaws wider than space
separating tooth bands on opposing premaxilla (narrowerin Filimanus and Pentanemus, see Feltes, 1991; Motomura etal., 2000c, 2001f,i); lip on anterior part of lower jaw either
well or poorly developed (absent in Eleutheronema, seeMotomura et al., 2002a); basisphenoid in contact with prootic (not in contact in Filimanus and basisphenoid absent
in Parapolynemus and Polynemus, see Feltes, 1991, 1993;
Motomura et al., 2001i); pectoral fin base including base ofpectoral filaments less than upper jaw length (greater in
Galeoides, see Feltes, 1993; Motomura et al., 2001b,e); anal
fin soft rays less than 18 (more than 24 in Pentanemus, seeFeltes, 1993); swimbladder absent or simple, not extending
beyond anal fin origin (swimbladder with many appendagesin Leptomelanosoma, see Motomura and Iwatsuki, 2001a,and swimbladder extending beyond anal fin origin in
Galeoides, see Feltes, 1993; Motomura et al., 2001b).
Polydactylus is distributed from tropical to temperateareas worldwide: 14 species currently recognized as valid
occurring in the Indo-Pacific (Motomura et al., 2000b,
2001a,c,d,g,i,j, 2002b; Motomura and Iwatsuki, 2001a,b),
2 species in the eastern Pacific (Allen and Robertson,
1994; Schneider, 1995; this study), 3 species in the western
Atlantic (Randall, 1978; Robins and Ray, 1986), and 1 species in the eastern Atlantic (Allen, 1981; Njock, 1990).

Polydactylus approximans(Lay and Bennett, 1839)(English name: blue bobo)(Spanish name: barbudo seis barbas)(Figs. 1A, 1B, 2A)
Polynemus approximans Lay and Bennett, 1839: 57 (type locality: San
Blas and Mazatlán, west coast of Mexico, based on a brief sketch anddescription by Mr. Collie).
Polynemus californiensis Thominot, 1886: 161 (type locality: California,
USA).
Material examined. 58 specimens, 24–228 mm SL. BMNH
1863.12.16.30 (previously regarded as 1 of 2 syntypes of Polynemus
approximans Lay and Bennett, see Remarks), 107 mm SL, Panama;
BMNH 1866.1.14.6 (previously regarded as 1 of 2 syntypes of
Polynemus approximans Lay and Bennett, see Remarks), 215 mm SL,
Panama; CAS 2823, 122 mm SL, Bathing beach, Acapulco Bay,
Guerrero, Mexico; CAS SU 6292, 186 mm SL, Lima, Bay of Callao,
Peru; CAS SU 35305, 183 mm SL, Monterey Bay, California, USA;
MNHN 1884–487 (holotype of Polynemus californiensis Thominot),179 mm SL, California, USA; USNM 15129, 123 mm SL, Panama;
USNM 41393, 174 mm SL, Panama; USNM 43265, 143 mm SL,
Guaymas, Gulf of California, Mexico; USNM 46488 (3 specimens), 78–
91 mm SL, San Juan, Mexico; USNM 46876, 183 mm SL, Panama;
USNM 47464, 225 mm SL, Mazatlán, Mexico; USNM 53517, 143 mm
SL, Ecuador; USNM 65621, 152 mm SL, Panama; USNM 77637, 161 mm
SL, Tumbes, Peru; USNM 79873 (2), 168–197 mm SL, Panama; USNM
82194, 61 mm SL, Chame, Panama; USNM 94015, 95 mm SL, Ecuador;
USNM 94041, 112 mm SL, Panama; USNM 114468 (5), 181–228 mm SL,
Guatemala; USNM 127891 (2), 122–188 mm SL, Puerto Pizarro, Peru;

Fig. 1. Polydactylus approximans (A, B) and Polydactylus opercularis(C, D). A MNHN 1884-487 (holotype of Polynemus californiensis
Thominot), 179 mm SL, California. B BMNH 1866.1.14.6 (previously
regarded as syntype of Polynemus approximans Lay and Bennett),
215 mm SL, Panama. C BMNH 1864.1.26.321 (holotype of Polynemus
melanopoma Günther), 263 mm SL, Guatemala. D USNM 41054,
179 mm SL, Panama
USNM 127892, 165 mm SL, Puerto Pizarro, Peru; USNM 127893, 96 mm
SL, Lobos de Tierra Island, Peru; USNM 177788 (1 of 8 specimens),
30 mm SL, off Nicaragua (11°58 N, 91°30 W); USNM 177789, 34 mm
SL, off Oaxaca, Mexico (15°24 N, 97°20 W); USNM 177808 (3), 92–
136 mm SL, San Blas, Nayarit, Mexico; USNM 181256, 24 mm SL, San
Jose, Guatemala; USNM 181276 (1 of 7 specimens), 60 mm SL, Gulf ofNicoya, Costa Rica; USNM 181280 (1 of 3 specimens), 37 mm SL,

360

Fig. 2. Geographic distribution of A Polydactylus approximans and
B Polydactylus opercularis, based only on specimens examined inthis study
22.4 km south of Maria Cleofas Island, Marias Islands, Mexico; USNM
220698, 138 mm SL, Jiquilisco, El Salvador; USNM 220779, 201 mm
SL, Jiquilisco, El Salvador; USNM 220784 (3), 136–148 mm SL, La
Caramba, Jiquilisco Bay, El Salvador; USNM 290055 (2), 151–155 mm
SL, Colombia; USNM 304426 (4), 56–82 mm SL, 8.32 km north ofMazatlán, Mexico; USNM 321984 (3), 101–138 mm SL, El Rompio,
Panama; USNM 321985, 205 mm SL, Chitré, Panama; USNM 366749(2), 109–133 mm SL, off Gulf of Fonseca, El Salvador; USNM 366761,
120 mm SL, off Gulf of Fonseca, El Salvador; USNM 366766, 75 mm SL,
off Gulf of Fonseca, El Salvador.

Diagnosis. A species of Polydactylus with the following
combination of characters: 6 (rarely asymmetrically 6 and 7,
2 of 58 specimens) pectoral filaments, longest filament notextending beyond level of posterior end of anal fin base; 56–

H. Motomura et al.

63 (mode 60) pored lateral line scales; lip on lower jaw
well developed, dentary teeth restricted to dorsal surface;vomerine teeth present; maxilla not covered with scales;
lateral line bifurcated on caudal fin membranes, extending
to posterior margins of upper and lower caudal fin lobes;
swimbladder present, small; body grayish, no stripes or
spots.
Description. Counts and proportional measurements aspercentages of SL of Polydactylus approximans, including
the holotype of Polynemus californiensis, are given in Table
1. Characters given in the diagnosis of the species are notrepeated here.
Body oblong, compressed; obtusely conical snout projecting strongly beyond upper jaw; occipital profile nearlystraight in young, becoming somewhat concave withgrowth; adipose eyelid well developed; posterior margin of
maxilla not reaching to or extending slightly beyond levelof posterior margin of adipose eyelid; lip on upper jaw
thin; teeth villiform in broad bands on vomer, palatines, andectopterygoids; tooth plate on palatines wider than those on
ectopterygoids; shape of vomerine tooth plate crescentic or
elliptic; posterior margin of preopercle serrated; all firstdorsal fin spine bases of similar thickness; first spine of firstdorsal fin very small; third spine of first dorsal fin longest,
posterior tip of third spine sometimes extending well beyond level of second dorsal fin origin; first spine of anal finvery small, third spine longest; bases of dorsal, pectoral,
anal, and caudal fin covered with scales; all pectoral fin rays
unbranched, posterior tip not reaching to or extending beyond level of posterior tip of pelvic fin; pectoral fin insertion
well below midline of body; first pectoral filament shortest,
just reaching to or extending slightly beyond level of pelvic
fin origin; second to fourth pectoral filaments extending
beyond level of pelvic fin origin; length of fifth pectoral
filament variable, from not reaching level with posterior
margin of pelvic fin to just reaching level with anal fin origin;sixth pectoral filament longest, just short of level of anal fin
origin or reaching to near midpoint of anal fin base; poorly
developed membranes present near base on dorsal margins
of pectoral filaments; caudal fin deeply forked, upperand lower caudal fin lobes not filamentous; formula for
configuration of supraneural bones, anterior neural spines,
and anterior dorsal pterygiophores 0/0/0  2/1  1/1/1/1/1/;
10  14 vertebrae.
Color when fresh.—Head and body gray dorsally, silver
ventrally; anterior margins of first and second dorsal fins
black, remaining parts dusky; pectoral fin dusky; base ofpectoral filaments white, becoming blackish on posterior
tips; base and posterior margin of pelvic fin white, remaining
parts dusky; posterior margin of anal fin white, remaining
parts dusky; margins of caudal fin black, remaining parts
dusky.
Color of preserved specimens.—Head and body brown
dorsally, pale yellowish-silver ventrally; first and second
dorsal, anal, and caudal fins uniformly pale yellow; intensityof pectoral fin pigmentation variable from dense black
to translucent; pectoral filaments pale yellow; base of pelvic
fin pale yellow, posterior margin of pelvic fin white or translucent, remaining parts grayish-black.

Revision of eastern Pacific Polydactylus

361

Table 1. Counts and measurements of eastern Pacific Polydactylus species, expressed as percentages of standard length
Polydactylus approximans

Standard length (mm)Counts
Dorsal fin rays
Anal fin rays
Pectoral fin rays
Pectoral filaments
Pelvic fin rays
Pored lateral line scales
Scales above/below lateral line
Gill rakers
Measurements
Head length
Body depth at 1st dorsal fin origin
Body depth at 2nd dorsal fin origin
Body width at pectoral fin base
Snout length
Dermal eye opening
Orbit diameter
Interorbital width
Postorbital length
Upper jaw length
Depth at posterior margin of premaxilla
Pre-1st dorsal fin lengthPre-2nd dorsal fin length
Preanal fin length
Pelvic fin origin to anal fin origin
Second dorsal fin base length
Anal fin base length
Longest pectoral fin length
Longest pectoral filament length
Pectoral fin base length
Longest pelvic fin ray length (1st)Longest 1st dorsal fin spine length (3rd)Second dorsal fin spine length
Longest 2nd dorsal fin ray length (2nd)Longest anal fin spine length (3rd)Longest anal fin ray length (2nd)Caudal peduncle length
Caudal peduncle depth
Upper caudal fin lobe length
Lower caudal fin lobe length

Polydactylus opercularis

Holotype of
Polynemus
californiensis
MNHN 1884-487

Non-types of
Polydactylus
approximansn  57

Holotype of
Polynemus
melanopoma
BMNH 1864.1.26.321

Non-types of
Polydactylus
opercularisn  53179

24–228263

19–309

VIII-I, 12
III, 14
15
6
I, 5
58
8/12
12  17  29

VIII-I, 11–13
III, 13–15
14–16
6–7
I, 5
56–63
7–8/11–13
11–14  15–18  26–31

VIII-I, 12
III, 13
16
9
I, 5
71
9/12
16  19  35

VIII-I, 11–13
III, 12–14
14–16
8–9
I, 5
66–74
7–10/12–15
13–18  17–20  31–37

29
27
29
12
4
6
7
8
17
13
4
35
62
58
22
15
23
25
34
10
16
22a
—
20a
8
18
22
15
35a
33a

28–35 (31)
25–32 (30)
29–34 (32)
10–16 (13)
5–6 (5)
6–7 (6)
7–8 (7)
7–8 (7)
16–21 (19)
13–15 (14)
3–4 (3)36–40 (38)
63–68 (65)
57–64 (64)
20–27 (23)
14–17 (15)
20–23 (22)
24–32 (28)
35–48 (41)
9–12 (10)
16–17 (16)
16–26 (23)
7–11 (9)22–26 (24)
6–10 (9)17–22 (20)
21–26 (23)
14–16 (15)37–43 (40)
35–40 (37)

32
26
25
12
5
5
7
7
22
18
4
36
61
68
31
15
16
22
32
10
16
19
7
19
6
18
22
12
35a
31a

29–33 (31)25–29 (27)
25–29 (27)
12–16 (13)
4–6 (5)
5–7 (6)
5–8 (7)
7–8 (7)
19–22 (20)
16–18 (17)
3–4 (3)
34–37 (35)
61–63 (62)61–68 (65)
23–31 (27)
14–16 (15)
16–18 (16)
20–24 (22)30–41 (36)
9–10 (9)14–17 (16)
17–21 (19)
6–8 (7)
18–21 (19)
6–8 (7)
16–20 (18)
21–23 (22)
11–13 (12)31–38 (35)
30–36 (33)Means in parentheses include type dataa
Tip slightly broken

Distribution and habitat. Polydactylus approximans iscurrently known from the eastern Pacific Ocean, where it
ranges from Monterey Bay, California, USA, to Callao, Peru
(Fig. 2A), being relatively common in the Central American
region in latitudes between 5° and 20° N. Grove andLavenberg (1997) reported a single small example (LACM
W53–178) collected from the Galápagos Islands, the species
normally being considered to occur rarely around theislands. Although Pequeño (1989) listed Polydactylus
approximans and Polydactylus opercularis from Chile, suchrecords remain unsubstantiated.
Although the species generally inhabits muddy or sandy
bottoms in coastal waters and estuaries, larvae and juveniles(less than ca. 40 mm SL) sometimes occur at the water
surface several hundred kilometers offshore (Grove andLavenberg, 1997). Most of the collection data available indi-362cate that the specimens were taken from depths less than
30 m.
Remarks. Polydactylus approximans was originallydescribed as Polynemus approximans by Lay and Bennett(1839), on the basis of a brief sketch and description by Mr.
Collie. Eschmeyer (1998) questioned the status of two
syntypes of Polynemus approximans, registered as BMNH
1863.12.16.30 and BMNH 1866.1.14.6 (see Fig. 1B), theoriginal description of the species giving no indication oftype specimens. Although the type locality of the species
was given as San Blas and Mazatlán, west coast of Mexico(Lay and Bennett, 1839), the collection data of the two
BMNH specimens indicated they had been collected fromPanama. Furthermore, according to Lay and Bennett(1839), Mr. Collie investigated the anatomy of the stomach,pyloric caeca, and intestine of the species. Although theabdomen of one of the two BMNH specimens (BMNH
1866.1.14.6) has been cut, the slit is very small and not
sufficient for observation of the internal organs. Moreover, the specimen used for the sketch by Mr. Collie
measured ca. 178 mm (probably TL) and 25 mm wide (Layand Bennett, 1839), whereas BMNH 1863.12.16.30 and
BMNH 1866.1.14.6 are 107 mm SL (caudal fin lobe tip damaged but ca. 141 mm TL) and 11 mm wide, and 215 mm SL(ca. 293 mm TL) and 30 mm wide, respectively. Accordingly,
we conclude that the two BMNH specimens of Polydactylus
approximans are not type material of Polynemus approximans, the original specimens most likely having beenlost.
According to the original description, Polynemus
approximans was characterized by having six pectoral filaments and grayish body color, characteristics consistent
with those of specimens considered here as Polydactylus
approximans. Although Lay and Bennett (1839) quoted theabsence of a swimbladder in the species from the brief
description by Mr. Collie, the presence of a swimbladder
was confirmed by our examination of seven USNM specimens (see Materials and Methods). The swimbladder wasapparently overlooked by Mr. Collie due to its very small
size (length ca. 13% of SL).
Polynemus californiensis was originally described byThominot (1886) from California, USA, on the basisof a single specimen (MNHN 1884–487, 179 mm SL; Fig.
1A). The only subsequent reference to the species wasby Blanc and Hureau (1971), who listed it as the same
species with Polydactylus approximans in the type catalogueof the Muséum national d’Histoire naturelle, giving neither
reasons nor an indication of materials examined. The
holotype of Polynemus californiensis has the following
characters: lip on lower jaw well developed, dentary teeth
restricted to dorsal surface; maxilla not covered withscales; lateral line bifurcated on caudal fin membranes,
extending to posterior margins of upper and lower caudal
fin lobes. These characters, and meristics and proportional
measurements (listed in Table 1) agreed well with those of
specimens considered here as Polydactylus approximans(see Table 1). Accordingly, Polynemus californiensis isherein regarded as a junior synonym of Polydactylus
approximans.

H. Motomura et al.

Polydactylus opercularis (Gill, 1863)(English name: yellow bobo)(Spanish name: barbudo nueve barbas)(Figs. 1C, 1D, 2B)
Trichidion opercularis Gill, 1863: 168 (type locality: west coast of Central America, probably Cape San Lucas, Baja California, Mexico; see
Remarks).
Polynemus melanopoma Günther, 1864: 148 (type locality: San José,
Guatemala).
Material examined. 54 specimens, 19–309 mm SL. BMNH
1864.1.26.321 (holotype of Polynemus melanopoma Günther), 263 mm
SL, San José, Guatemala; CAS SU 51242, 136 mm SL, off Chira Islands,
Gulf of Nicoya, Costa Rica; CAS SU 51252, 31 mm SL, Jalisco, Mexico;
USNM 41054, 179 mm SL, Panama; USNM 41218, 85 mm SL, Panama;
USNM 50343 (2 specimens), 210–236 mm SL, Panama; USNM 65622(3), 109–187 mm SL, Panama; USNM 76811, 215 mm SL, Panama;
USNM 79870, 270 mm SL, Panama; USNM 79871, 264 mm SL, Panama;
USNM 79878, 132 mm SL, Panama; USNM 119740, 137 mm SL,
Guaymas, Gulf of California, Mexico; USNM 127890, 309 mm SL, off
Puerto Pizarro, Peru; USNM 177799 (2), Sinaloa, Gulf of California,
Mexico; USNM 177800, Sonora, Gulf of California, Mexico; USNM
181254 (1 of 2 specimens), 19 mm SL, off Guerrero, Mexico (16°6 N,
100°19 W); USNM 181257, 27 mm SL, Malpelo Island, Colombia;
USNM 181262 (2), 47–48 mm SL, south of Corinto, Nicaragua; USNM
181287 (5), 140–160 mm SL, Topolobampo, Gulf of California, Mexico;
USNM 181320, 208 mm SL, San Blas, Nayarit, Gulf of California,
Mexico; USNM 200371, 267 mm SL, Tumbes, Peru; USNM 367307 (3),202–246 mm SL, Gulf of Panama, Panama; USNM 367308 (2), 158–
185 mm SL, south of Buenaventura, Colombia; USNM 367166, 174 mm
SL, off Punta Ampala, Gulf of Fonseca, El Salvador; USNM 367309(18), 159–252 mm SL, Punta Coco, Colombia.

Diagnosis. A species of Polydactylus with the following
combination of characters: 9 (rarely 8, 2 of 54 specimens;
asymmetrically 8 and 9, 1 of 54 specimens) pectoral filaments; 66–74 (mode 70) pored lateral line scales; anterior
parts of lower jaw with villiform teeth extending onto lateral surface, adjacent portion of lip poorly developed inlarger specimens; vomerine teeth present; maxilla covered
with small deciduous scales; lateral line unbranched, extending to upper end of lower caudal fin lobe; swimbladderabsent; body, especially fins, yellowish, no stripes or spots.
Description. Counts and proportional measurements aspercentages of SL of Polydactylus opercularis, including theholotype of Polynemus melanopoma, are given in Table 1.
Characters given in the diagnosis of the species are notrepeated here.
Body oblong, compressed; obtusely conical snout projecting strongly beyond upper jaw; occipital profile nearlystraight throughout life; adipose eyelid well developed;
posterior margin of maxilla extending well beyond level ofposterior margin of adipose eyelid; lip on upper jaw thin;teeth villiform in broad bands on vomer, palatines, andectopterygoids; tooth plate on palatines wider than thoseon ectopterygoids; shape of vomerine tooth plate nearlysquare; posterior margin of preopercle serrated; all first dorsal fin spine bases of similar thickness; first spine of firstdorsal fin very small; third spine of first dorsal fin longest,
posterior tip of third spine not reaching to level of second

Revision of eastern Pacific Polydactylus

dorsal fin origin; first spine of anal, fin very small, third spine
longest; bases of dorsal, pectoral, anal, and caudal fin covered with scales; all pectoral fin rays unbranched, posterior
tip not reaching to level of posterior tip of pelvic fin; pectoral fin insertion well below midline of body; first pectoral
filament shortest, not reaching to or extending slightly beyond level of posterior tip of pelvic fin; lengths of second to
ninth pectoral filaments similar, extending beyond level ofposterior tip of pelvic fin or level of anal fin origin, sometimes not reaching to level of posterior tip of pelvic fin;entire well-developed membranes present on dorsal margins of pectoral filaments; caudal fin deeply forked, upperand lower caudal fin lobes not filamentous; formula for
configuration of supraneural bones, anterior neural spines,
and anterior dorsal pterygiophores /0/0/2/1  1/1/1/1/1/;
10  14 vertebrae.
Color when fresh.—Head and body pale green dorsally,
silver ventrally; posterior margins of first and second dorsal
fins dark yellow, remaining parts dusky; pectoral fin dusky;base of pectoral filaments white, becoming yellow on posterior tips; posterior tip of pelvic fin yellow, remaining parts
white; base of anal fin white, remaining parts vivid yellow;
lower caudal fin lobe dark yellow, upper lobe dusky.
Color of preserved specimens.—Head and body brown
dorsally, yellowish-silver ventrally; first and second dorsal,
pectoral, anal, and caudal fins uniformly pale yellow;
pectoral filaments white.
Distribution and habitat. Polydactylus opercularis iscurrently known from the eastern Pacific Ocean (Fig.
2B), where it ranges from northern Los Angeles Harbor,
California, USA, to off Paita, Peru (Hildebrand, 1946), being relatively rare north of Baja California, Mexico. The
record from off Paita, Peru, was based on a single juvenile
specimen (12 mm total length; Hildebrand, 1946). The species generally inhabits muddy or sandy bottoms in coastal
waters and estuaries, but also occurs along sandy beaches(Allen and Robertson, 1994). Most of the collection data
available indicate that the specimens were taken from
depths less than 46 m.
Remarks. Polydactylus opercularis was originally described by Gill (1863) (as Trichidion opercularis) on thebasis of a single specimen, which has apparently been lost.
Although Gill (1863) gave no detailed locality for the holotype, the type locality having since been widely regarded
only as “west coast of Central America,” Hildebrand (1946)
noted the type locality of the species as Cape San Lucas,
Baja California, Mexico. Because the holotype had
been held in the National Museum of Natural History,
Smithsonian Institution, Washington, DC, USA (see Gill,
1863: 162), the collections to which Hildebrand had considerable access (see Hildebrand, 1946: 6), there is every
possibility that he had taken the information from a label
stored with the holotype before its loss. Accordingly, thetype locality of Trichidion opercularis is most likely Cape
San Lucas, Baja California, Mexico.
According to the original description, Trichidion
opercularis was characterized by having eight pectoral filaments and the anal fin tinged with orange, characteristics
consistent with those of specimens considered here as

363

Polydactylus opercularis. Subsequently, Günther (1864) described Polynemus melanopoma as a new species from San
José, Guatemala, on the basis of a single specimen (BMNH
1864.1.26.321, 263 mm SL; Fig. 1C). The taxonomic statusof that species has remained unquestioned to date, thespecies having apparently been overlooked by subsequent
researchers. Our examination of the holotype of Polynemus
melanopoma and the specimens considered here as Polydactylus opercularis showed that they represented a single
species (see Table 1). Accordingly, the former is herein
regarded as a junior synonym of Polydactylus opercularis.
Seale and Bean (1907) overlooked Gill’s (1863) Trichidion opercularis and described Polydactylus opercularis as a
new species on the basis of a single specimen (USNM 57844,
124 mm SL) from Zamboanga, Mindanao, Philippines.
Jordan and Richardson (1910) recognized this designation
as a secondary homonym, thereby providing the replacement name, Polydactylus sealei, for Seale and Bean’s Polydactylus opercularis. Although Jordan and Richardson(1910) considered Gill’s Trichidion opercularis and Seale
and Bean’s Polydactylus opercularis as belonging to thesame genus (Polydactylus), the former and latter are presently regarded as valid species, Polydactylus opercularis andFilimanus sealei, respectively (Feltes, 1991; this study).

ComparisonsComparisons of Polydactylus approximans with related
congeners. Polydactylus approximans and six Indo-Pacific
Polydactylus species, Polydactylus longipes Motomura,Okamoto and Iwatsuki, Polydactylus malagasyensis
Motomura and Iwatsuki, Polydactylus nigripinnis Munro,
Polydactylus persicus Motomura and Iwatsuki, Polydactylus
sexfilis (Valenciennes), and Polydactylus sextarius (Blochand Schneider), are characterized by having 6 pectoral filaments (Motomura et al., 2000a, 2001a,g; Motomura and
Iwatsuki, 2001b; Motomura and Senou, 2002). However,
Polydactylus approximans is distinguished from the othersix species by having a bifurcated lateral line (unbranchedin the latter). The lateral line condition of Polydactylus
approximans is also found in an Indian Ocean species,
Polydactylus bifurcus Motomura, Kimura and Iwatsuki, andall three currently recognized western Atlantic species,
Polydactylus octonemus (Girard), Polydactylus oligodon(Günther), and Polydactylus virginicus (Linnaeus) (seeMotomura et al., 2001d: fig. 3A). Polydactylus approximans
differs from the above four species in having usually 6
pectoral filaments (5 in Polydactylus bifurcus, usually 7 in
Polydactylus oligodon and Polydactylus virginicus, andusually 8 in Polydactylus octonemus; Motomura et al.,2001d).
Polydactylus approximans has a scale-less maxilla, thatcharacter also being found in the three western Atlantic
species and an eastern Atlantic species, Polydactylus
quadrifilis (Cuvier), other congeners (distributed in the
Indo-Pacific and eastern Pacific) having the maxilla withdeciduous scales, the size and number of scales being both
intra- and interspecifically variable.

29

—
3
—
9
—
13
—
14
—
10
—
2
10
2
20
—

36
35
34
33
32
31
30

Total gill rakers

—
1
—
11
10
38
45
4

14
—

37

—
1
—
2
2
43
42
8
11
—

15
13
12
11
/
10

9
—
3
—
1
—
—
11
—
29
12
12
33
1

26
20
19
18
17
16

Lower gill rakers

11
—

28
27

—
1
—
—
—
3
—
7
—
20
—
8
—
8
—
5

1
—
—
1
—
3
—
22
—
20
a

Anal fin ray counts based on 53 specimens

3
6
25
1
21
—
n  57n  53
P. approximans
P. opercularis

8
—

16
15
14
13
12
11

13
—
9
—
4
—
2
—
n  55n  54
P. approximans
P. opercularis

Upper gill rakers

15
—

8
—

3
—

17

1
—

18

—
—

15

—
2

73
71
67
66
—
63
61
58
56

57

3
6
n  58n  54aP. approximans
P. opercularis

11

59

54
45

12

60

1
3

13

62

Pored lateral line scales

37
2
16
48
—
3

12

13

14

68

69

5
—

15

70

5
6

14

72

45
40

15

74

8
8

16

7

8

56
—

9

Scales above/below lateral line

14

—
51
—
1
—
2
2
—

8/9
8/8
6/7
6/6

Pectoral filaments (right/left side)
Pectoral fin rays
Anal fin soft rays
Dorsal fin soft rays

Table 2. Frequency distributions of selected meristic characters of eastern Pacific Polydactylus species

Comparisons of Polydactylus opercularis with related
congeners. Polydactylus opercularis is easily distinguishedfrom its congeners by having usually 9 pectoral filaments(usually 4–8 filaments in the latter; see Motomura et al.,2000a,b, 2001a,c,d,g,j, 2002b; Motomura and Iwatsuki,
2001b; Motomura and Senou, 2002; this study). The pectoral
filaments in a western Atlantic species, Polydactylus
octonemus, although usually 8, infrequently number 9,
thereby overlapping with Polydactylus opercularis, which
has 8 pectoral filaments on rare occasions (Table 2). However, Polydactylus octonemus differs from the latter in having lower pored lateral line scale counts [mode 59 (range
56–64) vs. 70 (66–74) in the latter], well-developed lower jaw
lips throughout life (lips on anterior parts of lower jaws
poorly developed in larger specimens), and a swimbladder(absent).
The condition of the lower jaw lips and teeth (anterior
parts of lower jaw with villiform teeth extending onto
lateral surface, adjacent portion of lip poorly developed)
found in larger Polydactylus opercularis is unique among
the genus, although the condition is also found in all stagesof Leptomelanosoma indicum (Shaw), distributed in the
Indo-West Pacific (Motomura and Iwatsuki, 2001a), and inlarger Parapolynemus verekeri (Saville-Kent), occurringin southern New Guinea and northern Australia (Feltes,
1993).
Polydactylus opercularis lacks a swimbladder, such condition being found also in three Indo-West Pacific species,
Polydactylus multiradiatus (Günther), Polydactylus nigripinnis, and Polydactylus siamensis Motomura, Iwatsuki
and Yoshino (Motomura et al., 2001c, 2002b). Polydactylus
opercularis can be easily distinguished from the others byhaving 9 pectoral filaments (5 in Polydactylus siamensis, 6 in
Polydactylus nigripinnis, and 7 in Polydactylus multiradiatus;
see Motomura et al., 2001c, 2002b).
Comparisons between eastern Pacific Polydactylus.
Polydactylus approximans can be easily distinguished from
Polydactylus opercularis by having lower counts of pectoral
filaments [6 on each side (rarely asymmetrically 6 and 7)
or sometimes 5 on each side, according to Grove andLavenberg (1997) vs. 9 on each side (rarely 8 on each side orasymmetrically 8 and 9) in the latter], pored lateral line
scales [56–63 (mode 60) vs. 66–74 (70)], scale rows aboveand below the lateral line [7 or 8 (7) and 11–13 (12) vs. 7–10
(8) and 12–15 (13), respectively] and gill rakers [upper series
11–14 (13), lower 15–18 (17), and total 26–31 (30) vs. 13–18(16), 17–20 (19), and 31–37 (34), respectively], and higher
counts of anal fin soft rays [13–15 (14) vs. 12–14 (13)] (seeTable 2).
In addition to these meristic characters, Polydactylus
approximans differs from Polydactylus opercularis in having
the following distinct morphological characters: lip on lower
jaw well developed, dentary teeth restricted to dorsal surface (anterior parts of lower jaw with villiform teeth extending onto lateral surface, adjacent portion of lip poorly developed in larger Polydactylus opercularis); maxilla scale less(covered with small deciduous scales); lateral line bifurcated on caudal fin membranes, extending to posterior
margins of upper and lower caudal fin lobes (lateral line

H. Motomura et al.

9/9

364

Revision of eastern Pacific Polydactylus

unbranched, extending to upper end of lower caudal finlobe); swimbladder present (absent).
Comparative material examined. All from Atlantic Ocean.
Polydactylus octonemus: ANSP 22900 (syntype of Polynemus
octonemus Girard), 62 mm SL; USNM 739 (2 syntypes of Polynemus
octonemus Girard), 62–79 mm SL; USNM 15074 (holotype of
Trichidion octofilis Gill), 166 mm SL; USNM 48883, 164 mm SL; USNM
93603 (2 specimens), 86–102 mm SL; USNM 155666, 126 mm SL;
USNM 156107 (2), 73–113 mm SL; USNM 156112 (3 of 4 specimens),
73–114 mm SL; USNM 156119, 135 mm SL. Polydactylus oligodon:
BMNH 1848.1.12.890 (paralectotype of Polynemus oligodon Günther;
stuffed specimen), 146 mm SL; USNM 19961, 292 mm SL; USNM
120740, 135 mm SL; USNM 364370 (4), 111–113 mm SL. Polydactylus
quadrifilis: ISH (at ZMH) 298-1959, 214 mm SL; MNHN 756 (holotype
of Polynemus quadrifilis Cuvier; lacking caudal fin and half of caudal
peduncle), 380 mm from anterior tip of snout to posterior end of remaining peduncle; MNHN 1906-0212, 189 mm SL; MNHN 1967-0789(2), 181–231 mm SL; MNHN 1978-0355, 129 mm SL; MNHN 1979-0483,
147 mm SL; MNHN 1991-0918 (2), 128–132 mm SL; MNHN 1999–1104,
92 mm SL; MNHN 1999–1110, 74 mm SL; USNM 193684, 328 mm SL;
USNM 320435, 153 mm SL. Polydactylus virginicus: MNHN 5504
(syntype of Polynemus americanus Cuvier), 141 mm SL; MNHN A.
3028 (syntype of Polynemus americanus Cuvier), 157 mm SL; MNHN
A. 3031 (syntype of Polynemus americanus Cuvier), 121 mm SL; MSNG
6695 (holotype of Polynemus antillarum Perugia), 84 mm SL; USNM
9835, 155 mm SL; USNM 41324 (1 of 13 specimens), 149 mm SL; USNM
50145, 190 mm SL; USNM 79872 (2), 149–182 mm SL; USNM 79875,
186 mm SL; USNM 79877, 140 mm SL; USNM 156875, 189 mm SL;
USNM 185186, 110 mm SL; USNM 185330, 136 mm SL; USNM 185454,
152 mm SL; USNM 186064 (3), 122–138 mm SL; USNM 290237, 157 mm
SL; USNM 367193, 146 mm SL; USNM 367194, 167 mm SL. Comparative materials from Indo-Pacific are listed in Motomura et al. (2000a–c,
2001a–j, 2002a–c), Motomura and Iwatsuki (2001a,b), Motomura andSenou (2002), and Motomura and Sabaj (2002).
Acknowledgments We are grateful to the following persons and institutions for specimen loans and providing references: M.H. Sabaj(ANSP); J. Maclaine (BMNH); W.N. Eschmeyer, T. Iwamoto, D.
Catania, and J. Fong (CAS); P. Pruvost and G. Duhamel (MNHN); S.L.
Jewett, J.T. Williams, L. Palmer, S.J. Raredon, S. Smith, and K. Hoshino(USNM), and H. Wilkens (ZMH). We also thank Y. Motomura(Hiratsuka, Japan) for her assistance and G.S. Hardy (Ngunguru, New
Zealand), who read the initial manuscript and offered helpfulcomments. This study was supported in part by a grant awarded to thefirst author by Research Fellowships of the Japan Society for the
Promotion of Science for Young Scientists (Tokyo, Japan).

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