Bull. Natl. Mus. Nat. Sci., Ser. A, Suppl. 2, pp. 85–96, March 21, 2008

Platygobiopsis tansei, a New Species of Dorso-ventrally
Flattened Gobiid Fish from Southern Japan
Muneo Okiyama
Marine Ecology Research Institute, Teikoku-shoin Bldg, 5F,
Jinbo-cho 3–29, Kanda, Chiyoda-ku, Tokyo 101–0051, Japan
E-mail: bb8m-okym@asahi-net.or.jp

Abstract A new species of Platygobiopsis, P. tansei, is described on the basis of 22 specimens,
23.0–46.8 mm SL, from depths of 60–136 m in southern Japan. It is easily distinguished from its
congener, P. akihito, in having more second dorsal-fin rays (14–15 vs 12), fewer gill rakers on thefirst gill arch (09–10 vs 1–311–12), absence of chin barbels, less extensive scale development
around nape and pectoral-fin base, absence of pelvic-fin frenum, and absence of sensory-canalpores and cutaneous folds on head. Its osteology is described with special references to its unusually depressed head and body. Platygobiopsis tansei from temperate waters is a smaller and deeperdwelling form than its tropical congener, P. akihito.
Key words : Platygobiopsis tansei, new species, dorso-ventrally flattened goby, southern Japan.

Platygobiopsis was established on the basis ofan unusually depressed head and body for a goby.
The type and hitherto only known species, P. akihito Springer and Randall, 1992, was collectedfrom Flores, Indonesia. This paper describes a
new and second species of Platygobiopsis fromsouthern Japan, with special reference to modifications of its osteology resulting from its depressed head and body. Although Springer andRandall (1992) briefly mentioned the existence of
this new species citing my unpublished information, morphological and ecological aspects ofthese 2 congeners are compared in much greater
detail here.
Materials and Methods
Counts, measurements and terminology follow
those of Springer and Randall (1992), including
the spinous dorsal-fin pterygiophore formula proposed by Birdsong et al. (1988), and cutaneous
papillae and cephalic sensory pore nomenclatureused by Lachner and McKinney (1978, 1979).
Definitions of median fin elements are based on
Birdsong (1975), but those of the caudal fin including the caudal-fin formula (number of dor-sal unbranched raysdorsal hypaxial branched
rays/ventral hypaxial branched raysventral unbranched rays) follow Fujita (1990). NSMT-P
33283 was cleared and double stained for bone
and cartilage as outlined in Potthoff (1984).
NSMT-P 77004 and 77005 were stained only forbone. Institutional abbreviations follow Leviton
et al. (1985).

Platygobiopsis tansei sp. nov.
(New Japanese name: Beta-haze)(Figs 1–3, Table 1)
Holotype. NSMT-P33282, ?, 46.8 mm SL. Off
Kunozan, 37°55.9N, 138°30.6E, Suruga Bay, Sizuoka
Prefecture, Japan, muddy sand substratum, 92–120 m, 2 m
beam trawl, R/V Tansei-maru, 17 July 1978.
Paratypes. NSMT-P 33283, 1 (/, 40.5), and NSMTP 77001–77003, 3 (26.8, 27.0, 27.3), taken with holotype;
NSMT-P 77004–77006, 3 (26–32.9), off-Kunozan,
34°55.5N, 138°30.6E, 62–90 m, 2 m BT, R/V Tanseimaru, 17 July 1978; NSMT-P 77007, 1 (33.9), offKunozan, 34°55.0N, 138°30.4E, 120–136 m, 2 m beam
trawl, R/V Tansei-maru, 17 July 1978; NSMT-P
77008–77010, 3 (23.0, 30.5, 31.1), off-Kunozan,
34°57.0N, 138°27.8E, 72–125 m, 2 m beam trawl, R/V
Tansei-maru, 12 June 1977; NSMT-P 19015, 3 (43.9,
48.2, 1 specimen not measured), 36°47.5N, 141°51.0E,86

M. Okiyama

Fig. 1. Platygobiopsis tansei, NSMT-P 33282, holotype, 46.8 mm SL, male, the Suruga Bay. A: left side in lateral view; B: ventral view of pelvic-fin.

Fig. 2. Photographs of Platygobiopsis tansei, NSMT-P 33282, holotype, 46.8 mm SL. A: left side in lateralview; B: dorsal view.
960–970 m (questionable record, see Discussion), R/V
Soyo-maru, 21 June 1976; NSMT-P 77011, 1 (34.5),
34°35.2N, 137°46.1E, 117 m, Smith-McIntyre grab,
R/V Seisui-maru, 19 Sep. 1984; FAKU 50551, 1 (?,43.0), 32°47.5N, 129°42.0E, 60–70 m, Smith-McIntyre
grab, 19 Sep. 1981, R/V Yoko-maru; BSKU 19127, 1(33.6), 34°58.2N, 140°04.2E, 100 m, R/V Soyo-maru;
BSKU 20122 (36.9), 20123 (44.4), 20124 (44.5), 20125(31.7), 34°58.6N, 140°01.2E, 61–87 m, R/V Soyo-maru,
4 Mar. 1960.

Diagnosis. A species of Platygobiopsis withthe following combination of characters: dorsalfin rays VI, I, 13–14; outer gill rakers on first gillarch 09–10; chin barbel absent; predorsal
scales extending anteriorly to transverse line
through middle of operculum; scales absent frompectoral-fin base; no cephalic sensory-canalpores; pelvic-fin frenum absent.
Description. Dorsal-fin rays VI-I, 13–14;
anal-fin rays I, 12–14; pectoral-fin rays 15–17;

pelvic-fin rays I, 5; caudal-fin rays 5–68/7
4–5; branchiostegals 5; lateral scales approximately 50–59; predorsal scales approximately
12–13; first arch gill rakers 09–10; vertebrae
1016; posteriormost pleural rib on 9th vertebra(sometimes as vestigial); posteriormost epineuralon 17th vertebra.
Body elongate, remarkably depressed andwide, with moderately compressed caudal peduncle. Head small, broader than body, snout rounded in dorsal view. Eyes horizontally ovoid, dorsal
half partly projecting above top of head. Mouth
slightly oblique, posterior tip of maxilla extending to a vertical through anterior edge of eye.
Conical teeth closely arranged in 2 and/or 3 rows
on upper jaw, with larger, inwardly curved teeth
scattered in outermost series, decreasing to single
row posteriorly. Conical teeth of similar size
arranged closely in several rows in anterior four-New Gobiid Species of Platygobiopsis

87

Table 1. Morphometric proportions in % of standard length of Platygobiopsis tansei. Holotype is NSMT-P
33282.

Standard length, mm
Head length
Head width
Snout length
Orbit diameter
Postorbital length
Abdomen length
Body depth
Pelvic-fin length
Pectoral-fin length
Caudal-fin length
Caudal-peduncle length
Predorsal length

NSMT-P
33282

NSMT-P
19015

NSMT-P
19015

FAKU
50551

NSMTP33283

Smallparatypes(n10)

46.8(?)
22.6
16.2
4.5
4.1
15.0
31.9
12.6
16.0
20.3
26.0
17.5
31.0

48.2(?)
20.7
13.7
3.1
4.5
12.4
25.3
6.6
13.6
17.6
26.5
18.2
27.2

43.9(/)
21.1
14.0
4.3
3.6
13.2
28.2
7.3
14.3
16.6
—
15.9
30.2

43.0(?)
23.5
15.0
3.5
5.4
15.0
30.4
5.8
16.9
13.1
36.5
15.4
33.1

40.5(/)
21.2
18.8
3.2
4.2
13.8
29.1
8.1
16.5
16.5
25.4
17.3
32.1

23.0–33.9
23.5–26.0
13.9–18.6
3.5–4.5
3.2–5.7
11.2–16.3
25.7–33.9
5.8–11.2
15.2–20.9
13.1–26.4
14.2–36.5
13.9–19.2
31.6–35.1

fifths of lower jaw, with larger, slightly curved
teeth anteriorly. No teeth on vomer or palatine.
Tongue truncate. First gill arch with 9 rakers
along outer edge of distal two-thirds of ceratobranchial, rakers moderately long and slenderwith pointed tips, decreasing in length anteriorly;
similar or fewer numbers (less than 9) of short
tooth patches present along outer (except for 1st
gill arch) and inner edges on all ceratobranchials.
Gill opening wide, lower opercular membrane attached to isthmus below posterior margin of preopercle. Anterior nostril tubular, directed ventrally, reaching tip of upper jaw; posterior nostril
without raised rim, lying close to anteriormost
edge of orbit. Chin barbels absent. Head naked,
without head pores. Large sagitta (otoliths) forming incomplete ‘v’ pattern in dorsal view withsagitta from opposite side of skull readily observed through thin cranial bone. Cephalic sensory papilla pattern complicated (Fig. 3), comprising 2 prominent horizontal (dorsal, ventral),fleshy, papillae-bearing cheek folds (dcf andvcf); 3 opercular folds (aof, hof, and vof); an extensive lateral longitudinal fold (llf); a short median longitudinal fold (mlf); a ventrolateral fold(vlf); and a most extensive preoperculomandibular fold (pom). Scales exclusively cycloid, size
varying according to section of body, arranged
rather irregularly. Scales on nape extending anteriorly to a transverse line through midlength of

operculum; scales on breast extending anteriorly
to slightly behind branchiostegal membrane;
belly scaled; scales extending posteriorly to caudal base; head, occipital region and pectoral-finbase naked.
Origin of first dorsal fin slightly posterior topectoral-fin base; outline of fin somewhat rounded. Second dorsal-fin separated from first by
broad space; dorsal fins subequal in height, rays
not elongated. Anal fin originates below base of
first ray of second dorsal fin, and ends below last
ray; height as for second dorsal fin. All soft rays
in second dorsal and anal fins branched and segmented distally; last 2 rays slightly longer thanpreceding ones, closely set, split to base, counted
as 1. Pelvic fins elongate, united medially by awell-developed connecting membrane between
innermost rays; frenum absent; all rays branched
once deeply, then subdivided distally into 4 (1stand 5th rays), 5 (2nd and 4th) or 8 (3rd) branches, with approximately distal two-thirds finely
segmented.; pelvic fin not reaching posteriorly tolevel of 6th dorsal-fin spine when adpressed. Pectoral fins elongate, slightly pointed, their lengths
17–24% SL; all but dorsalmost rays branched
once distally; distal halves of almost all rays finely segmented. Caudal fin elongate, moderately
pointed; distal two-thirds of dorsal and ventral
branched rays and neighboring ones segmented.
Urogenital papillae of both sexes moderately

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M. Okiyama

Fig. 3. Positions of cephalic sensory organ and papillae-bearing holds in Platygobiopsis tansei, NSMT-P 33282,
holotype. A: dorsal view; B: left side in lateral view; C: ventral view. aof: arching opercle fold, dcf: dorsal
cheek fold, hof: horizontal opercle fold, llf: lateral longitudinal fold, mlf: median longitudinal fold, pom: preoperculomandibular hold, vcf: central cheek fold, vlf: ventrolateral fold.

developed in specimens larger than 40 mm SL;
slender, pointed in males; wider, less pointed,
pigmented mid-ventrally in female.
Gut nearly straight or slightly curved at midway depending on body size; stomach and pyloric caecum indistinct.
Color in spirit (when well preserved as in Fig.
2). Head and body dark brown dorsolaterally;
ventral portions unpigmented except for several
small internal spots midventrally; a series of 6slightly darker saddles on body, each associatedwith somewhat broad midlateral stripe; first at

pectoral-fin base, second, broader than others,
along base of first dorsal fin, and following 3 ofsimilar width, evenly spaced along 2nd dorsal-finbase, and last on caudal peduncle; all fins almost
transparent other than dark band extended frombody onto caudal fin. Color patterns slightly variable, often difficult to discriminate particularly insmaller specimens.
Osteology: Cranium (Fig. 4). Cranium
strongly depressed, slightly deeper posteriorly,
without distinct supraoccipital crest, relative
sizes of length, width, and depth about

New Gobiid Species of Platygobiopsis

1 : 0.74 : 0.23. Vomer toothless, broadened anteriorly, flattened dorsoventrally, posteriorly produced as narrow long process. Median ethmoid
broadened anteriorly, flattened dorsoventrally,
with narrow posterior process. Lateral ethmoids
slender, elongate, projecting sideways, proximally based on median ethmoid, distally in contact
with lachrymals. Frontals very narrow between
orbits, widening in postorbital region, posterolaterally in broad contact with wing-like sphenotic
and pterotic, posteriorly with supraoccipital andepiotic; anterior and lateral borders of epioccipital and lateral junction between sphenotic andpterotic separated by cartilage. Supraoccipital89

with narrow posterior extension between epiotics
through epioccipitals. Parasphenoid forming
main floor of skull, broadest at junction between
sphenotics and prootics, progressively narrowing
towards posterior end at about two-thirds of basioccipital length. Small intercalar surrounded byprootic, pterotic, epioccipital and basioccipital inventral view.
Jaws, suspensorium, and opercular series(Fig. 5). Rostral cartilage barrel-shape, withshallow groove posteroventrally, lying on anteriorbroad part of vomer. Nasal bone absent. Premaxilla with trapezoidal crest-like post premaxillary
process along rear half of upper edge. Maxilla

Fig. 4. Neurocranium of Platygobiopsis tansei, NSMT-P33283, paratype. A: dorsal view; B: ventral view. bo:basioccipital, eo: exoccipital, ep: epioccipital, f: frontal, int: intercalar, le: lateral ethmoid, me: median ethmoid, p: parasphenoid, pro: prootic, pte: pterotic, r: rostral cartilage, so: supraoccipital, sph: sphenotic, v:
vomer. Cartilage is stippled.

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M. Okiyama

with prominent anterior head and long shaft, posteriorly modified into well developed posteroventral process, tipped with cartilage. Dentary withclosely set teeth on anterior four-fifths of length,
followed by produced large toothless coronoid
process; ventrally, a medial cartilaginous shelf ispresent. Articular cartilaginous anteroventrally,
with slender Meckel’s cartilage along long dorsal
ramus. Retroarticular distinct. Palatine T-shaped,with shaft extending ventrally to about half of ectopterygoid length; ectopterygoid shaft straight,
articulating broadly with anterior edge ofquadrate. No mesopterygoid. Palato-pterygoquadrate complex and associated opercular components remarkably tilted posteriad, including
wide suspensorial interspace (sensu Harrison,1989). Hyomandibular with extensive anterior(articulating with sphenotic) and posterior (articulating with opercle) cylindrical struts, andsmaller strut articulating with prootic. Preopercle
and interopercle horizontally extended forward
along quadrate. Opercle triangular with rounded
tip bearing needle-like posterior filament; subopercle leaf-like, anteriorly hooked, terminating in
sharply pointed tip posteriorly: dorsal and ventral
margins of opercle and ventral margin of subopercle cartilaginous.
Gill arch and hyoid apparatus (Fig. 6A–D).
Anterior tip of basihyal flat with cartilaginous
margin; small cartilaginous basibranchial 1 attaching to anterodorsal depression of urohyal,with large interspace separating it from basi-

branchial 1; basibranchials 2 and 3 elongate, wellossified; basibranchial 4 small, cartilaginous; 5
slender ceratobranchials with tooth plate only on
dorsomedial sides of 5th; long gill rakers restricted to outer edge of ceratobranchial 1; hypobranchials 1–3 (hb1–3) short, variously modified
distally, with cartilaginous tips on both ends ofhypobranchials 2–3. Upper gill arch comprising
epibranchials 1–4, infrapharyngobranchials 2–4,
and interarcural cartilage; epibranchial 4 uniquely robust, without cartilage-tipped uncinate
process; infrapharyngobranshial 3 largest, notfused with contiguous bones (pb 2, 4). Urohyal
with low lateral keels, posteriorly diverging intolong dorsal and short ventral projections separated by deep indentation. Hyoid apparatus slenderfor entire length, branchiostegal rays inclined
strongly posteriorly from attachments to hyoidbones. Dorsal and ventral hypohyals present.
Short interhyal with small anterior and posterior
processes, dorsally attaching by ligament to hyomandibular at posterior cartilaginous corner
below posterior horizontal cylindrical strut, laterally to medial surface of preopercle. Five branchiostegal rays similarly elongate; branchiostegal
1 very slender, articulating with ventral surfaceof narrow anterior process of ceratohyal; branchiostegals 2–5 blade-like (2 and 5 noticeably
broader at both ends), 2–4 articulating with outerventrolateral surface of anterior ceratohyal and 5with posterior ceratohyal; all branchiostegals,
and particularly 5, distally cartilaginous.

Fig. 5. Jaw, suspensorium, and opercular series of Platygobiopsis tansei, NSMT-P 33283, paratype. Left side inlateral view. art: articular, d: dentary, h: hyomandibular, iop: interopercle, m: Meckel’s cartilage, mx: maxilla,
mpt: metapterygoid, pal: palatine, pmx: premaxilla, pop: preopercle, ptg: ectopterygoid, q: quadrate, ra:retroarticular, sop: subopercle, sy: symplectic. Cartilage is stippled.

New Gobiid Species of Platygobiopsis

91

Fig. 6. Gill arch and hyoid bones of Platygobiopsis tansei, NSMT-P33283, paratype. A: lower gill arch in dorsal
view; B: upper gill arch of left side in ventral view; C: urohyal, left side in lateral view; D: hyoid apparatus,
left side in lateral view. ach: anterior ceratohyal, bb1–4: basibranchials 1–4, bh: basihyals, br: branchiostegals, cb1–5: ceratobranchials 1–5, cl: cleithrum, dh: dorsal hypohyal, eb1–4: epibranchials 1–4, hb1–3: hypobranchials 1–3, iac: interarcular cartilage, ih: interhyal, pb2–4: infrapharyngobranchials 2–4, pch: posterior
ceratohyal, uh: urohyal, vh: ventral hypohyal. Cartilage is stippled.

Paired fins and girdles (Fig. 7A–C) Pectoral
girdle nearly at right angle between short supracleithrum and crescent-shaped long cleithrum.
Posttemporal narrowly forked anteriorly, withlonger dorsal process twisted proximally to form
low exterior lateral keel, ligamentously bound toepiotic; ventral process slender, short, attachedonly to epioccipital. Cleithrum tilted posteriad,
comprising deeply forked dorsal portion, robust
middle portion with remarkable arch-shaped lateral flange arising medially from broad main
stem, and ventral portion of broad flat bone withprominent lateral spine (tentatively termed “ventral outer cleithral spine: vocs) and articular
process for pelvic girdle; small ventral intercleithral cartilage present. Four proximal radials ofsimilar size, each tipped with cartilage on bothanterior and posterior ends, proximally supported

by extensive scapular-coracoid cartilage withsmall foramen anterodorsally; distal radials present for all but dorsalmost pectoral-fin rays.
Coracoid bound to ventral half of middle portionof cleithrum, with obtuse spine at posteroventral
corner. No postcleithrum.
Pelvic girdle reversed trapezoid shape indorsoventral view; pelvic bone remarkably flat,anteriorly tipped with gently concave, laterally
raised pelvic intercleithral cartilage, posteriorly
with linear cartilaginous pelvic radials except forslightly produced central post pelvic process;ventromedial postpelvic processes short, slender,
fully contiguous, anteroventrally deflected.
Vertebrae and unpaired fins (Fig. 8, Fig. 7D).
Vertebrae 1016 including urostylar element;
caudal vertebrae defined exclusively by presenceof haemal spine with broad arch. Parapophyses

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M. Okiyama

Fig. 7. Pectoral- and pelvic girdles, and caudal skeleton of Platygobiopsis tansei, NSMT-P 33283, paratype. A:
Ppctoral girdle, left side in lateral view; B: distal part of cleithrum in ventral view; C: pelvic girdle in ventral
view; D: caudal skeleton, left side in lateral view. ap: articular process for pelvic girdle, cihpu: inter-haemal
cartilage, cinpu: inter-neural spine cartilage, cl: cleithrum, cor: coracoid, epu: epural, cphpu2: post-haemal
spine cartilage of pu2, hpu2: haemal spine of pu2; hyp1–5: hypurals 1–5, npu2: neural spine of pu2, pb:
pelvic bone, phy: parhypural, pr: proximal radial, per: pelvic radial, picc: pelvic intercleithral cartilage, pp:
postpelvic process, ptm: posttemporal, sca: scapula, pu2: preural vertebra 2, scl: supracleithrum, vic: ventral
inter cleithral cartilage, vocs: ventral outer cleithral spine. Cartilage is stippled.

(sensu stricto) blade-like, remarkably expanded
laterally on vertebrae 2–10, most extensive
around 8th, with basis at anterior end of respective neural arch, progressively angled from horizontal to diagonal posteriorly; homologous
blade-like structure probably termed parapophysis (sensu lato) distinct at base of haemal spineof vertebrae 11–19.
Vertebrae 1–17 with epineurals; first epineural
directly attached to lateral swelling at anterior
end of vertebra 1, remainders to dorsal side ofparapophyses (sensu lato) of vertebra 2–17. Pleurals on vertebra 3–9 (vestigial on right side ofvertebra 9 in NSMT-P 33283, Fig. 8) attaching toslightly distal positions of respective epineurals;intermuscular bones forming laterally expanded
arches. Dorsal pterygiophore formula 3-22110(sensu Birdsong et al., 1988). Dorsal- and analfin supports closely bound to vertebrae. Spinous

dorsal-fin
pterygiophores
modifiedintoboomerang-like bones as deep as long. Second
dorsal-fin pterygiophores except both first andlast comprising partly or fully cartilaginous proximal, medial, and distal radial; no middle radial
in first pterygiophore; no middle and distal radials in last pterygiophore. All but last anal-fin
pterygiophores with equal set of radials; no medial and distal radials in last pterygiophore. Twoanal-fin pterygiophores present anterior to firsthaemal spine (AP2), with posterior one longer
and more strongly inclined.
Caudal skeleton (Fig. 7D) vertically narrow,comprising typical urostylar vertebra with relatively short, slender hypural 5 and large, broadbased epural; ventral hypural plate (hyp12) autogenous, dorsal hypural plate (hyp34) fusedwith ural centrum; parhypural long, slender, well
separated from compound ural centrum. Neural

New Gobiid Species of Platygobiopsis

Fig. 8. Vertebrae and dorsal- and anal-fins supports of Platygobiopsis tansei, NSMT-P 33283, paratype. A: anterior vertebrae and dorsal- and anal fins, left side in lateral view; B: first four (v1–4) and middle four (v9–12)
vertebrae and intermuscular bones in ventral view. Pleural ribs and epineurals are not shown in A. ap: anal-fin
pterygiophore, d2p: second dorsal-fin pterygiophore, epl: epineural, hs1: first haemal spine, n: neural spine,
pl: pleural, pph: parapophysis, sdp: spinous dorsal-fin pterygiophore, v: vertebra. Cartilage is stippled.

Fig. 9. Distributions of Platygobiopsis tansei. Symbol in Suruga Bay represents several localities in the neighbourhood.

93

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M. Okiyama

spine of preural centrum 2 (pu2) broad based, as
low as preceding neural spine; haemal spine ofpu2 particularly stout, long, extending posteriorly
opposite to tip of epural. Main components of
dorsal and ventral procurrent cartilages, i.e.,
cinpu3, cihpu3chpu2 (sensu Fujita, 1990), similarly elongate and paralell each other.
Etymology. “Tansei” here used as a noun inapposition, refers to the research vessel Tanseimaru of the Ocean Research Institute, Universityof Tokyo (now, of the Japan Marine Science andTechnology Center) responsible for collecting
many Suruga Bay specimens including the holotype.
Discussion
Distribution (Fig. 9). Collecting localities ofthis new species were scattered along the Pacificcoast of southern Japan ranging from off the
Fukushima Prefecture to Nagasaki Prefecture.
Although the northernmost locality is represented by 2 specimens, this record is problematic, because the reported bottom depth of capture is unusually deep (960–970 m). Other specimens werecollected exclusively from shallower bottoms between 65 and 128 m, and no other gobioids haveever been recorded from depths greater than
500 m; Obliquogobius turkayi Goren, collected at
depths of 434–496 m in the central Red Sea(Goren, 1992), probably represents the deepest
record of occurrence for a gobioid. Common occurrences of 2–5 specimens in a single tow of a
2 m or similarly large beam trawl indicate considerable abundance of P. tansei in the relevant
depth zone of southern Japan. Platygobiopsis
tansei can be referred to the “burrowers” (sensu
Miller, 1993) ecological radiation of the gobioid
fishes, as well as to the”deep water type” (sensu
Takagi, 1966) of gobies defined as inhabiting relatively deep sandy mud bottom of the continental
shelf.
In Suruga Bay, P. tansei was often found inbeam trawl collections containing a lot of sandy
mud sediments, probably due to the less than flatbottom configuration of the habitat. In addition,collections of 2 specimens (FAKU 50551,
NSMT-P 77010) by a Smith-McIntyre grab are
noteworthy. Platygobiopsis tansei is thus a true
benthic species in the sloping sandy mud bottoms, often residing in the bottom sediment itself.
Comparison. In general morphology, Platygobiopsis tansei closely resembles P. akihito. As
indicated in the species diagnosis, however, P.
tansei can be discriminated from P. akihoto inhaving more second dorsal-fin rays (14–15 vs 12
in P. akihoto), fewer gill rakers on 1st gill arch
(09–10 vs 1–311–12), absence of chin barbels and pelvic-fin frenum, distribution pattern ofscales on dorsal surface of head (extending anteriorly to a vertical through middle of operculumvs. extending anteriorly well beyond a verticalthrough posterior margin of preopercle) and pectoral-fin base (naked vs. scaled), all scales onbody cycloid (vs. cycloid anteriorly, ctenoid posteriorly), and no cephalic sensory-canal andpores (vs. present). Both species have essentiallythe same cephalic sensory papilla patterns, except for the less extensive lateral longitudinalfold and dorsal cheek fold in P. tansei. Althoughboth species have 1016 vertebrae, P. tansei has
the posteriormost pleural ribs on the 8–9th (vs9–10th in P. akihito) vertebrae, and posteriormost
epipleurals on the 16–17th (vs 19–21th in P. akihito) vertebrae. Most of these differences possibly illustrate more retrogressive trends in P. tansei than in P. akihito. Additionally, so far as is
known, P. tansei appears to be a smaller anddeeper-living species than P. akihito: maximum
known sizes ca. 50 mm SL (N22 specimens) vs96.4 mm SL (N12 specimens) and deepest collection depths (61 m vs 15–17 m).
Remarks. Some gobioids such as Rhyacichthys aspro (Milller, 1973) and Anatifrostrum
profundorum (Ahnelt et al., 2000) have amarkedly depressed head or snout, but their
trunks are generally less specialized. Platygobiopsis, as its name implies, represents the mostextremely dorso-ventrally flattened form among
gobies in general.
Major osteological specializations of P. tansei

New Gobiid Species of Platygobiopsis

are probably modifications resulting from its depressed and/or associated wide body form: (1)the axial skeleton, particularly the head and longitudinally modified jaw and suspensorium, as
well as the appendicular skeleton such as dorsaland anal-fin pterygiophores are specifically modified into narrow organization; (2) the pectoral
girdle is sharply angled at its junction with thetypical supracleithrum and the elongate broad
cleithrum; (3) the posttemporal is narrowly
forked to allow for its attachment to the depressed skull; (4) the attachment of the pleuralribs and epipleurals have been displaced far laterally on the unusually wide parapophyses; and (5)ventral portions of the head skeleton (lower jaw,
branchiostegals, and some opercular bones) arecharacterized in having their peripheral areas cartilaginous.
Despite its unusual osteological specializations, P. tansei exhibits the typical elements of ageneralized gobiid skeleton as discussed by several recent authors (Miller, 1973; Birdsong,
1975; Springer, 1983; Harrison, 1989; Hoese andGill, 1993; Winterbottom, 1993; Johnson andBrothers, 1993).
Acknowledgements
The author wishes to thank the crew and scientific party of the R/V Tansei-maru cruises (Ocean
Research Instituite) in collecting specimens.
Thanks are also due to Y. Machida and H. Endo
(BSKU), T. Miura (MUFS), T. Nakabo (FAKU),
K. Matsuura and G. Shinohara (NSMT) for theirkind permission to study a part of paratype specimens. Hiroshi Senou (KPM) and Junichi Kojima(MERI) kindly assisted in preparing somefigures. Special thanks are extended to K.
Shibukawa (NSMT), V. G. Springer (USNM) and
two anonymous reviewers for their critical comments on the manuscript including constructive
suggestions to improve it.
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Manuscript received 20 June 2007; revised 16 January
2008; accepted 24 January 2008.
Associate editor: K. Matsuura