Polydactylus bifurcus, a new species of threadﬁn from
Lombok Island, Indonesia (Perciformes: Polynemidae)
Hiroyuki Motomura1*, Seishi Kimura2, and Yukio Iwatsuki3
1

Miyazaki University, the United Graduate School of Agricultural Sciences, Kagoshima University, 1-1 Gakuen-kibanadai-nishi,
Miyazaki 889-2192, Japan (e-mail: a02113u@cc.miyazaki-u.ac.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: October 19, 2000 / Revised: April 21, 2001 / Accepted: April 25, 2001

IchthyologicalResearch©The Ichthyological Society of Japan 2001

Abstract Polydactylus bifurcus sp. nov. is described on the basis of a single specimen
collected from Lombok Island, Indonesia. The new species is distinguished from all otherIndo-Paciﬁc Polydactylus species by the following combination of characters: 15 pectoral
ﬁn rays, 5 pectoral ﬁlaments, 69 pored lateral line scales, 30 gill rakers, second spine of ﬁrst
dorsal ﬁn very strong and lateral line bifurcated on caudal ﬁn base, extending to posterior
margins of upper and lower caudal ﬁn lobes.

Ichthyol Res (2001) 48: 299–305
Key words

D

Polynemidae · Polydactylus bifurcus sp. nov. · Indonesia

uring a survey of the Indonesian ﬁsh fauna, a single
example of an undescribed species of Polydactylus
Lacepède, 1803 with ﬁve pectoral ﬁlaments was collectedfrom Lombok Island, Indonesia in 1996. The genus
Polydactylus, distributed from tropical to temperateareas worldwide, is deﬁned by a simple tooth plate on thevomer, the tooth band on the upper and lower jaws wider
than the space separating the tooth bands on the opposing premaxilla, the basisphenoid in contact with theprootic, the pectoral ﬁn base (including the base of thepectoral ﬁlaments) being less than the upper jaw lengthand a simple swimbladder, not extending beyond theanal ﬁn origin (Feltes, 1993; Motomura and Iwatsuki,2001). The new species could be distinguished from allother Indo-Paciﬁc Polydactylus species by the lateralline, which was bifurcated on the caudal ﬁn base andextended to the posterior margins of the upper and lower
caudal ﬁn lobes, whereas other congeners in the area
have an unbranched lateral line.
Efforts by the authors to collect further examples of
the new species during subsequent surveys of the Indonesian ﬁsh fauna were unsuccessful. The new species is
described herein, detailed comparisons being made withfour related species, also characterized by ﬁve pectoralﬁlaments.

Methods
Counts and measurements generally followed Hubbs
and Lagler (1947) and Feltes (1991), with some modiﬁcations following Motomura et al. (2000). Standard lengthis abbreviated as SL. Terminology of the supraneural andepineural bones follows Mabee (1988) and Patterson
and Johnson (1995), respectively, and the formula for
conﬁguration of the supraneural bones, anterior neuralspines and anterior dorsal ﬁn pterygiophores follows
Ahlstrom et al. (1976). Osteological characters wereconﬁrmed from radiographs of the holotype, and theswimbladder condition was conﬁrmed by dissection of
the abdomen on the right side of the body. Institutional
codes follow Eschmeyer (1998), with an additional institutional abbreviation as follows: Division of Fisheries
Sciences, Miyazaki University, Japan (MUFS).

Polydactylus bifurcus sp. nov.
(New English name: slender ﬁveﬁnger threadﬁn)(Figs. 1, 2, 3A)
Holotype. NSMT-P 60494, 144 mm SL, Kuta beach,
Lombok Island, Indonesia, 12 July 1996, beach seine net in
1.5 m, collected by S. Kimura and T. Peristiwady.

Diagnosis. A species of Polydactylus with the following combination of characters: 15 pectoral ﬁn rays; 5

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H. Motomura et al.

Fig. 1. Holotype of Polydactylus bifurcus sp. nov., NSMT-P 60494, 144 mm SL, Lombok Island, Indonesia

Fig. 2. First dorsal ﬁn of Polydactylus bifurcus sp. nov. Bar
5 mm

pectoral ﬁlaments; 69 pored lateral line scales; 30 gillrakers; second spine of ﬁrst dorsal ﬁn very strong (2.5times width of third spine; Fig. 2); lateral line bifurcatedon caudal ﬁn base, extending to posterior margins ofupper and lower caudal ﬁn lobes (Fig. 3).
Description. Proportional measurements of the holotype of Polydactylus bifurcus are given as percentagesof SL. Characters given in the diagnosis are not repeated.

Dorsal ﬁn rays VIII-I, 13; anal ﬁn rays III, 11; pectoral
ﬁn rays 15; pectoral ﬁlaments 5; pelvic ﬁn rays I, 5; pored
lateral line scales 69; scales above and below lateral line
9/12; gill rakers 12 (upper) ⫹ 18 (lower) ⫽ 30 (total);standard length 144 mm; head length 28; body depth 27;
second body depth 27; body width at pectoral ﬁn base 13;
snout length 5; dermal eye opening 6; orbit diameter 7;
interorbital width 8; postorbital length 17; upper jaw
length 14; pre-1st dorsal ﬁn length 34; pre-2nd dorsal ﬁnlength 60; pre-anal ﬁn length 60; 1st dorsal ﬁn origin toanal ﬁn origin 39; pelvic ﬁn origin to anal ﬁn origin 26;
2nd dorsal ﬁn base length 16; anal ﬁn base length 15;
longest pectoral ﬁn length 19; longest pectoral ﬁlament
length (4th) 38; pectoral ﬁn base length 9; longest pelvic
ﬁn ray length (1st) 17; longest 1st dorsal ﬁn spine length(3rd) 20; 2nd dorsal ﬁn spine length 10; longest 2nd dorsal ﬁn ray length (2nd) 24; longest anal ﬁn spine length(3rd) 9; longest anal ﬁn ray length (2nd) 21; caudal peduncle length 27; caudal peduncle depth 13; upper caudal
ﬁn lobe length 38; lower caudal ﬁn lobe length 37.
Body oblong, compressed; maxilla covered with scales;
orbit diameter greater than snout length; lower lip
well-developed; posterior margin of maxilla extending
beyond level of posterior margin of adipose eyelid; depthof posterior portion of maxilla shorter than dermal eye
opening; teeth villiform, in broad bands on vomer, palatines and ectopterygoids; all pectoral ﬁn rays unbranched; third pectoral ﬁlament longest, extending
beyond posterior tips of caudal ﬁn lobes; fourth pectoralﬁlament longest, not reaching to anal ﬁn origin; second
dorsal ﬁn base longer than anal ﬁn base; distance between pelvic and anal ﬁn origins less than head length;

New species of Polydactylus

Fig. 3. Lateral line squamation on caudal ﬁn membrane in (A)Polydactylus bifurcus sp. nov. (NSMT-P 60494, 144 mm SL) and(B) Polydactylus plebeius (MUFS 14125, 160 mm SL). Bars
5 mm

swimbladder well-developed; lower tip of seventh proximal pterygiophore of ﬁrst dorsal ﬁn directed forward;
formula for conﬁguration of supraneural bones, anterior
neural spines and anterior dorsal pterygiophores 0/0/
0⫹2/1⫹1/1/1/1⫹1/; vertebrae 10 ⫹ 14; 6 epineurals.
Fresh color notes.—Based on a color transparencyof the holotype from Lombok Island, Indonesia:

301

upper sides of head and trunk tinged silvery-green, becoming more silver on lower sides; ﬁrst and second dorsal ﬁns dark green; pectoral ﬁn white, becoming darkgreen on posterior tip; pectoral ﬁlaments and pelvic ﬁnwhite; anterior part of anal ﬁn dark green, remainderof ﬁn white; upper, lower and posterior margins of
caudal ﬁn black, remainder of ﬁn dark green (lower lobe
darkest).
Color of preserved specimens.—Head and body lightbrown dorsally, pale brown ventrally; tip of membrane
between third and ﬁfth spines of ﬁrst dorsal ﬁn darkbrown; anterior and posterior margins of second dorsal
ﬁn dark brown, remainder of ﬁn brown; pectoral ﬁnbrown, becoming blackish on posterior tip; pectoralﬁlaments and pelvic ﬁn brown; posterior part of anal
ﬁn dark brown, remainder of ﬁn brown; upper, lower
and posterior margins of caudal ﬁn blackish-brown,
other parts brown; eight faintly dark stripes along longitudinal scale rows above lateral line.
Distribution and habitat. Polydactylus bifurcus sp.
nov. is currently known only from Lombok Island, Indonesia. Collection data for the only known specimen
indicated that it was taken in shallow water (1.5 m) overa muddy bottom.
Etymology. The speciﬁc name bifurcus is derived
from Latin, meaning bifurcation, in reference to thebifurcated lateral line on the caudal ﬁn base, extending
to the posterior margins of the upper and lower caudal
ﬁn lobes.
Remarks. Polydactylus bifurcus sp. nov. can be distinguished from all other Indo-Paciﬁc Polydactylus species by having the lateral line bifurcated on the caudal ﬁnbase, extending to the posterior margins of the upper andlower caudal ﬁn lobes (vs. an unbranched lateral line in
the latter; Fig. 3). However, one of two East Paciﬁc species, P. approximans (Lay and Bennett, 1839), and all of
three Atlantic west coast species, P. octonemus (Girard,1858), P. oligodon (Günther, 1860) and P. virginicus(Linnaeus, 1758), have a lateral line condition similar to
P. bifurcus. Polydactylus bifurcus differs from these 4
species in having 5 pectoral ﬁlaments (vs. usually 6 in P.
approximans, 8 in P. octonemus and 7 in P. oligodon and
P. virginicus) (see Randall, 1978; Allen and Robertson,1994). Polydactylus approximans rarely has 5 pectoralﬁlaments, but the species is clearly distinguished from P.
bifurcus by the numbers of the pored lateral line scales
and anal ﬁn soft rays (55–60 and 13 or 14 [Grove andLavenberg, 1997] vs. 69 and 11, respectively, in the latter).
The lateral lines of the other East Paciﬁc species, P.
opercularis (Gill, 1863), and one West African species,
P. quadriﬁlis (Cuvier in Cuvier and Valenciennes, 1829),
are unbranched and extend to the upper end of thelower caudal ﬁn lobe (Fig. 3B).

302

Twelve nominal species with 5 pectoral ﬁlaments havebeen recorded from the Indo-Paciﬁc (Motomura et al.,2000, 2001): Polydactylus agonasi Jordan and McGregor,
1906, P. zophomus Jordan and McGregor in Jordan and
Seale, 1907, Polynemus commersonii Shaw, 1804, P. emoi
Lacepède, 1803, P. lineatus Lacepède, 1803, P. lydiae
Curtiss, 1938, P. macrochir Günther, 1867, P. microstomus
Bleeker, 1851, P. niloticus Shaw, 1804, P. plebeius
Broussonet, 1782, P. sheridani Macleay, 1884 and P.
taeniatus Günther, 1860. Recently, Polydactylus
macrochir, which is endemic to northern Australia andsouthern New Guinea, was redescribed as a senior synonym of Polynemus sheridani by Motomura et al. (2000).
Furthermore, 7 of the remaining 10 nominal species, viz.
Polydactylus agonasi, Polynemus commersonii, P. emoi, P.
lineatus, P. lydiae, P. niloticus and P. taeniatus have beensynonymized under Polydactylus plebeius, a widely distributed Indo-Paciﬁc species, by Motomura et al. (2001).
Of the remaining 2 nominal species, Weber and deBeaufort (1922) treated Polydactylus zophomus as a junior synonym of P. microstomus (action concurred withhere), being recognized as a valid species (e.g., Munro,
1967; Shen, 1984).
Recently, Motomura et al. (2001) described Polydactylus siamensis with 5 pectoral ﬁlaments from Thailand.
Accordingly, 5 species, viz. P. bifurcus sp. nov., P.
macrochir, P. microstomus, P. plebeius, and P. siamensis,
are now recognized as valid Indo-Paciﬁc Polydactylus
species with 5 pectoral ﬁlaments.
Further comparison of P. bifurcus with 4 otherspecies with ﬁve pectoral ﬁlaments showed the former tohave the lower tip of the seventh proximal pterygiophore of the ﬁrst dorsal ﬁn directed forward (vs. directedbackward in the latter) and the conﬁguration formula forthe supraneural bones, anterior neural spines, and anterior dorsal pterygiophores as 0/0/0⫹2/1⫹1/1/1/1⫹1/(vs. 0/0/0⫹2/1⫹1/1/1/1/1/) (Table 1). A similar anteriorly
directed seventh proximal pterygiophore of the ﬁrst
dorsal ﬁn has also been found in Leptomelanosoma
indicum (Shaw, 1804) (see Motomura and Iwatsuki,2001).
Polydactylus bifurcus further differs from P. microstomus in having higher counts of pored lateral line scales
and scales above and below the lateral line (69 and 9/12,
respectively, vs. 46–49 and 6 or 7/8–10, respectively, inthe latter), unbranched pectoral ﬁn rays (vs. almost
branched), fourth pectoral ﬁlaments longest (vs. ﬁfth
longest), teeth present on the vomer (vs. absent) and alarge black spot absent anteriorly on the lateral line (vs.
present) (see Table 1).
Like P. bifurcus, P. plebeius and P. siamensis, are characterized by several dark stripes along the longitudinalscale rows above the lateral line. However, the new spe-

H. Motomura et al.

cies is distinguished from the others by having higher
counts of the pored lateral line scales (69 vs. 60–66, rarely
68 and 54–58 in P. plebeius and P. siamensis, respectively),
fourth pectoral ﬁlaments longest (vs. ﬁfth longest) and avery strong second spine of the ﬁrst dorsal ﬁn (morerobust than other spines of ﬁrst dorsal ﬁn vs. similar toother spines) (see Table 1).
Polydactylus bifurcus is most similar to P. macrochir inhaving higher counts of pored lateral line scales andscales above and below the lateral line, unbranchedpectoral ﬁn rays, fourth pectoral ﬁlaments longest, teeth
present on the vomer and a very strong second spine of
the ﬁrst dorsal ﬁn (see Table 1). However, the former
differs from the latter in having the posterior margin of
the maxilla extending slightly beyond the level of theposterior margin of the adipose eyelid (vs. extending
considerably beyond in the latter) and lower counts ofgill rakers (30 vs. 32–35) (see Table 1).
Comparative material examined. Polydactylus approximans: BMNH 1863.12.16.30 (1 of 2 syntypes of Polynemus
approximans), 108 mm SL, Panama; BMNH 1866.1.14.6 (1 of 2
syntypes of P. approximans), 215 mm SL, Panama. Polydactylus
microstomus: AMS I. 10471, 158 mm SL, Manila, Luzon Island,
Philippines; FMNH 40769, 121 mm SL, Iloilo, Panay Island,
Philippines; FMNH 47393, 80 mm SL, Manila Bay, Luzon Island, Philippines; FMNH 47411 (2 specimens), 79–80 mm SL,
Iloilo, Panay Island, Philippines; FMNH 90792 (2), 96–102 mm
SL, 12.8 km offshore of Mandapam, Tamil Nadu, India; FMNH
91310, 84 mm SL, 12.8 km offshore of Mandapam, Tamil Nadu,
India; FRLM 15773, 91 mm SL, Kuta, Lombok Island, Indonesia; FRLM 23518, 116 mm SL, Passo, Baguala Bay, Ambon,
Indonesia; FRLM 23520, 101 mm SL, Passo, Baguala Bay,
Ambon, Indonesia; FSKU-P 20101, 96 mm SL, Nuguria Island,
Papua New Guinea; MUFS 14159, 154 mm SL, mouth of
Ouenghi River, New Caledonia; MUFS 18543, 78 mm SL,
Makassar (⫽ Ujung Pandang), Sulawesi, Indonesia; NTM S.
14607-009, 140 mm SL, Pasar Oeba, Kupang, West Timor, Indonesia; PMBC uncatalogued, 81 mm SL, Bangrong, eastern
Phuket Island, Thailand; RMNH 33552 (8), 76–132 mm SL, Bali,
Sumbawa, Sulawesi, Ambon and Seram, Indonesia and New
Guinea; USNM 113209, 148 mm SL, Manila, Luzon Island, Philippines; USNM 113210 (4), 78–148 mm SL, mouth of Santiago
River, Pagapas Bay, Luzon Island, Philippines; USNM 278196,
148 mm SL, Kampung Loleba, Halmahera Island, Indonesia;
USNM 278211 (10), 115–131 mm SL, Talemaninar, Gulf ofMannar, Sri Lanka; ZMH 13649, 128 mm SL, New Guinea;
ZMH 13650, 88 mm SL, Manila Bay, Luzon Island, Philippines.
Polydactylus octonemus: USNM 739 (2 of 2 syntypes of
Polynemus octonemus), 62–79 mm SL, Brazos, Santiago, Texas,
USA. Polydactylus oligodon: FMNH 92391, 92529 (2), 117–
129 mm SL, Para, Brazil. Polydactylus opercularis: USNM
41054, 184 mm SL, Panama; USNM 119740, 138 mm SL, south
Guaymas, Mexico. Polydactylus quadriﬁlis: ISH at ZMH
298-1959, 214 mm SL, Guinea, Africa. Polydactylus virginicus:
FMNH 3249, 216 mm SL, Vieques, Puerto Rico; FMNH 89620,
175 mm SL, Surinam. Collection data for the specimens of
Leptomelanosoma indicum, Polydactylus macrochir, and P.
plebeius and P. siamensis were given by Motomura and15, all unbranched

69

9/12

30

Extending slightly
beyond level ofposterior margin of
adipose eyelid

Present

Forward0/0/0⫹2/1⫹1/1/1/1⫹1/

Pectoral ﬁn rays

Pored lateral line
scalesScales above/below
lateral line

Gill rakers

Posterior margin of
maxillaTeeth on vomer

Direction of lower tipof seventh proximal
pterygiophore of ﬁrst
dorsal ﬁn

Formula for conﬁgurationof supraneural bones,
anterior neural spines
and anterior dorsal
pterygiophores

P. bifurcus sp. nov.
n⫽1
144 mm SL

0/0/0⫹2/1⫹1/1/1/1/1/

Backward

Present

Extending considerably
beyond level ofposterior margin of
adipose eyelid

34 (32–35)

9 (8–11)/12 (12–15)

72 (70–76)

Mode 14 (range
14–15), allunbranched

P. macrochiran ⫽ 3658–442 mm SL

Table 1. Selected characters of ﬁve Polydactylus species with ﬁve pectoral ﬁlaments

0/0/0⫹2/1⫹1/1/1/1/1/

Backward

AbsentReaching to (orslightly short of)level of posterior
margin of adipose
eyelid29 (24–33)

6 (6–7)/10 (8–10)

47 (46–49)

13 (13–15), almost
branched

P. microstomusn ⫽ 42
76–158 mm SL

0/0/0⫹2/1⫹1/1/1/1/1/

Backward

Present

Reaching to (orextending slightly
beyond) level ofposterior margin of
adipose eyelid

26 (24–32)

8 (8–9)/12 (12–13)

63 (60–66, rarely 68,
1 of 96 specimens)

17 (16–18, rarely 15,
1 of 100 specimens),
all unbranched

P. plebeiusbn ⫽ 114
43–331 mm SL

0/0/0⫹2/1⫹1/1/1/1/1/

Backward

Present

Extending slightly
beyond level ofposterior margin of
adipose eyelid

23 (22–24)

7/11 (10–11)

56 (54–58)

15, all unbranched

P. siamensisb
n⫽8
144–274 mm SL

New species of Polydactylus
303

Moderate, 38% of SL,
4th longest

Eight faint dark stripes
along longitudinalscale rows above
lateral line

Lombok Island,
Indonesia

Longest pectoral ﬁlaments
lengthBody color

Distributionb

From Motomura et al. (2000)
From Motomura et al. (2001)

Bifurcated, extending toposterior margins ofupper and lower
caudal ﬁn lobes

Lateral line squamation
on caudal ﬁnaMore robust than otherspines of ﬁrst dorsal
ﬁnP. bifurcus sp. nov.
n⫽1
144 mm SL

Second spine of ﬁrst
dorsal ﬁn

Table 1. Continued

Northern Australia
and southern New
GuineaNo stripes or spots

Long, mean 46%(range 40–53%) of SL,
4th longest

Unbranched,extending to upper
end of lower caudal
ﬁn lobeMore robust thanother spines of ﬁrst
dorsal ﬁn

P. macrochiran ⫽ 3658–442 mm SL

Eastern Indian Ocean
and West Paciﬁc(from east coast ofIndia to New
Caledonia)

A large black spot
anteriorly on lateralline

Short, 26%(21–30%) of SL,
5th longest

Unbranched,extending to upper
end of lower caudal
ﬁn lobeSlightly more robust
than or similar toother spines of ﬁrst
dorsal ﬁn

P. microstomusn ⫽ 42
76–158 mm SL

Indo-Paciﬁc (fromSouth Africa to
Tahiti)Seven or 8 prominent
dark stripes along
longitudinal scalerows above lateralline, 7–9 faintstripes below

Moderate, 32%(22–40%) of SL,
4th or 5th longest

Unbranched,extending to upper
end of lower caudal
ﬁn lobeSimilar to other spinesof ﬁrst dorsal ﬁn

P. plebeiusbn ⫽ 114
43–331 mm SL

Thailand (Gulf ofThailand andAndaman Sea)

Seven or 8 prominent
dark stripes along
longitudinal scalerows above lateralline, 7–9 faintstripes below

Moderate, 36%(31–43%) of SL,
5th longest

Unbranched,extending to upper
end of lower caudal
ﬁn lobeSimilar to otherspines of ﬁrst dorsal
ﬁn

P. siamensisb
n⫽8
144–274 mm SL

304
H. Motomura et al.

New species of Polydactylus
Iwatsuki (2001), Motomura et al. (2000), and Motomura et al.
(2001), respectively.
Acknowledgments We greatly appreciate the following persons and institutions for specimen loans: M. McGrouther and
K. Parkinson (AMS); J. Maclaine (BMNH); M.A. Rogers and
K. Swagel (FMNH); H. Ida and M. Okamoto (FSKU-P); K.
Matsuura and G. Shinohara (NSMT-P); H.K. Larson, B. Russell,
G. Dally and S. Gregg (NTM); U. Satapoomin (PMBC); M.J.P.
van Oijen and J. van Egmond (RMNH); S.L. Jewett, L. Palmer,
S.J. Raredon, and J.T. Williams (USNM); H. Wilkens (ZMH).
We are grateful to T. Yoshino (URM-P) and Y. Motomura(Miyazaki, Japan) for their assistance. Lastly, we thank G.S.
Hardy (Thames, New Zealand), who read the initial manuscript
and offered helpful comments. This study was supported in partby a grant awarded to the ﬁrst author by Research Fellowshipsof the Japan Society for the Promotion of Science for Young
Scientists (Tokyo, Japan).

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