Eugnathogobius microps Smith, 1931

Larson, Helen K., 2009, Review Of The Gobiid Fish Genera Eugnathogobius And Pseudogobiopsis (Gobioidei: Gobiidae: Gobionellinae), With Descriptions Of Three New Species, Raffles Bulletin of Zoology 57 (1), pp. 127-181 : 140-143

Eugnathogobius microps Smith, 1931

( Figs. 11–13 ; Tables 3–6, 9)

? Glossogobius mas Hora, 1923: 742–743 , Fig. 23 (Chilka Lake: off Samal Island, Rambha Bay, off Barkul).

Eugnathogobius microps Smith, 1931: 37 , Fig. 18 (Bangpakong River, Siam). – Koumans 1931: 68–69; Koumans 1940: 129, 200; Smith 1945: 520; Suvatti 1950: 421 (not seen); Suvatti 1981: 202; Kottelat 1989: 19; Eschmeyer & Bailey 1990: 145; Larson 2001: 68.

Eugnathogobius macrops – Herre 1940: 24 (lapsus).

Material examined. – THAILAND: Holotype of Eugnathogobius microps, USNM 90316, 1(26), lower Bangpakong River, central Thailand, H. M. Smith, 1 Jul.1923. USNM 119591 , 1 (26), same data as holotype; USNM 119593 , 3 (20.0–26.5), near Pitrieu, Bangpakong River , H. M. Smith, 4 Jun.1928; KUMF uncatalogued, 2(17.5–17.5) Bang Nara River , Narathiwat Province, D. Tanwilai, 23 Dec.1983; NTM S.13953-013, 7(18.0–25.5), small mangrove creek, Klong Bang Sai, Phuket Island, H. K. Larson, D. F. Hoese & PMBC staff, 8 Dec.1993.

Other material examined (but not used in description). Two specimens, KUMF 1853, near Pitrin, Bangpakong River, H. M. Smith, 4 Jun.1928 (fish very fragile, heads separated from bodies).

Diagnosis. – Small, stocky Eugnathogobius with slightly depressed head; second dorsal and anal rays I,6; pectoral rays 16–20; longitudinal scales 23–27; TRB 8–9; predorsal scales absent in specimens from central Thailand, 10–12 predorsal scales present in southern (peninsular) specimens; pectoral girdle smooth or with low fleshy flange; eyes small, mostly dorsal and close to snout tip; mouth terminal, large, may be greatly enlarged in males; tongue deeply bilobed; plain grey in colour, with blackish markings along bases of dorsal, anal, caudal and pectoral fins; known only from estuarine to fresh waters of Thailand.

Description. – Based on 13 specimens, 17.5–26.5 mm SL. An asterisk indicates counts of male holotype (illustrated in Larson 2001: Fig. 60).

First dorsal VI * (in 12), V (in one); second dorsal I,5–6* (mean I,6); anal always I,6*; pectoral rays 16-20 (mean 19, 18 in holotype); segmented caudal rays 17*; caudal ray pattern 9/8 (11)*; branched caudal rays 8/7* to 9/7 (modally 8/7); unsegmented (procurrent) caudal rays 7/7 or 8/7 (modally 8/7); longitudinal scale count 23–27* (mean 24); TRB 8*–9 (mean 9); predorsal naked in central Thailand specimens, 10–12 in peninsular Thailand specimens (mean 11); circumpeduncular scales 12*. Gill rakers on outer face of first arch 2+9 (in one), 3+9 (in one), 3+10 (in one). Pterygiophore formula 3-12210* (in eight). Vertebrae usually 10+16* (in 11); 10+15 (in one), 11+16 (in one). Neural spines of first few vertebra straight, pointed (in seven). Two * epurals (in nine). Two * anal pterygiophores before haemal spine of first caudal vertebra (in nine), three in one specimen. Anterior tip of preoperculum blunt ( Fig. 11 ) .

Body stout, somewhat depressed anteriorly, compressed posteriorly. Body depth at anal fin origin 18.5–23.1% (mean 21.3%) of SL. Head depressed anteriorly, always wider than deep, HL 31.3–35.4% (mean 33.9%) of SL; cheeks often considerably inflated. Depth at posterior preopercular margin 53.3–63.2% (mean 59.3%) of HL. Width at posterior preopercular margin 63.9–86.4% (mean 76.4%) of HL. Mouth large, terminal, slightly oblique, forming angle of about 30° with body axis; jaws reaching well past rear of eye in some males and to below rear half of eye in females (nearly to preopercular angle in male holotype). Lips smooth and without fimbriae, not very fleshy; lower lip mostly free, fused at tip of jaw. Upper jaw 45.2–69.6% (mean 48.4% in females, 63.0% in males) of HL. Eyes small, mostly dorsally oriented and close to snout tip and nostrils, 12.0–21.0% (mean 17.5%) of HL. Snout broad, blunt and flattened, 22.4–26.6% (mean 25.2%) of HL. Interorbital broad, flat, 23.9–31.6% (mean 27.8%) of HL. Caudal peduncle compressed, length 23.5–28.6% (mean 25.9%) of SL. Caudal peduncle depth 12.6–14.6% (mean 13.8%) of SL.

First dorsal fin low, first to fourth spines longest or subequal; spines usually not reaching second dorsal fin origin when depressed (rays of USNM specimens, including holotype, flabby and mostly wrinkled); spine tips in some specimens reaching front part of fin. First and second dorsal spine length 14.3% of SL (in 1). Third dorsal spine length 10.0–13.7% (mean 12.7%) of SL. Fourth dorsal spine length 10.0–12.2% (in 2) of SL. Second dorsal and anal fins low, posteriormost rays longest, rays falling well short of caudal fin base when depressed. Pectoral fin oval, central rays longest, 21.3–26.7% (mean 24.1%) of SL; rays usually all branched (upper and lowermost rays sometimes unbranched). Pelvic fins oval, central rays usually reaching anus, 24.2–27.2% (mean 25.6%) of SL. Caudal fin short, round, 22.5–29.1% (mean 25.7%) of SL.

Chin with very low bilobed mental fraenum (distinguishable in fresh specimens, but not in types). Nostrils very close together, just in front of eye. Anterior nostril with short tube, oriented down and forward over upper lip, preorbital slightly inflated to accommodate nostril. Posterior nostril oval, without raised rim, placed halfway between eye and anterior nostril. Gill opening usually extending forward to under opercle. Inner edge of shoulder girdle smooth with no ridge or flange (in six) or with low fleshy flange on upper half of girdle (in seven). Gill rakers on outer face of first arch very short and unspined, longest rakers near angle of arch; rakers on inner face of first arch also stubby, but slightly bigger than outer rakers; inner and outer rakers on other arches smooth, stubby, equal in size to the first arch inner rakers. Tongue large, deeply bilobed. Outer teeth in upper jaw larger than others, relatively small but sharp and curved; behind outer row, two to three rows of very small sharp teeth present; inner rows ending at anterior third of jaw. In males, teeth present on anterior half or two-thirds of upper jaw; in females, teeth present on anterior two-thirds to three-quarters of jaw. Lower jaw with teeth mostly across front only, with outer row of small pointed curved teeth and two to four inner rows of very small sharp teeth; only outermost row of teeth present at side of jaw. Both males and females with teeth restricted to front of lower jaw; outer row extending halfway along side in females and along one third of jaw length in males.

Predorsal scales, if present, small, mostly evenly sized, usually reaching forward to behind eyes; often only single scale anteriormost, in centre of nape close to interorbital space (this scale and its immediate neighbours may be somewhat enlarged). Specimens from the Bangpakong River with scales extending only partly over operculum, but predorsal naked. Operculum with small cycloid scales in peninsular Thailand specimens, naked in Bangpakong specimens. Cheek always naked. Pectoral base covered with cycloid scales (peninsular) or naked (Bangpakong). Prepelvic area covered with small cycloid scales (peninsular) or naked (Bangpakong). Belly scales cycloid (peninsular) or naked (Bangpakong). Ctenoid scales on side of body in wedge, close up to behind or just above pectoral base.

Genital papilla in male slender flattened and pointed, with one to several tiny lobes at tip; in female, papilla bulbous, rounded to slightly pointed.

Head pores absent.

Sensory papillae pattern longitudinal, as in Fig. 12 . Papillae rows g, x, z, b, d, e and opercular series consisting of small, closely spaced papillae. Papillae rows s, p, a, c, cp and i include widely spaced, relatively large papillae. Three s rows present, each consisting of one papilla. Row e well separated from preopercular margin, running almost vertically or turning anteriorly. Row d forming curved arch, posteriormost end always pointing downward (not rearward). Row f consisting of two papillae only, crowded behind mental fraenum.

Colouration of fresh material. – Fresh specimens collected from Phuket in 1993 were noted as being “plain dark greyish brown”; unfortunately they were not photographed.

Three months after preservation, the fish looked very similar to their remembered live colour, other than the pale underside appears to have become accentuated.

Head and body dark greyish-brown, with belly and underside of head paler (varying among individuals). Thin, very dark brown edge on scales on sides of body (especially rear half of body) and tiny dense brown spot often present at base of each scale. Cheeks paler than interorbital, front of head and preorbital region, which are usually darker brown than rest of head. Papillae rows dark brown; sometimes distinctly contrasting with rest of head colour. Isthmus whitish to white.

Fins translucent. Dorsals, anal, pectorals and caudal with band of dense dark brown pigment along bases, extending short distance onto fin rays and membranes. Pectoral sometimes with greyish brown patch on base of fraenum, sometimes narrow brownish edge to fraenum. Iris dark gold with dark brown mottling mostly obscuring gold colour. Genital papilla and area around anus white (usually streak of grey-brown on each side of male papilla).

Colouration of preserved material. – Available preserved specimens have generally lost all markings (other than the specimens from Phuket, described above) ( Fig. 13 ). The two uncatalogued KUMF specimens from the Bang Nara River have dusky heads, a small spot at the base of each body scale and some scattered melanophores on the underside of the head and breast.

Distribution. – Specimens are known only from central and peninsular Thailand. However, three specimens were obtained in October 2008 by Koichi Shibukawa (in litt.) from near the mouth of Tien River, Mekong drainage system, in southern Vietnam.

Ecology. – The holotype was collected by a pongpang (= tidal bag-net) net from “...the swift, tidal [estuarine] part of the Bangpakong River, where small gobies abound in both species and individuals” ( Smith, 1931). Later Smith collected specimens from Petrieu (= Paetriu; also spelled Pitrieu on one label), a town on the Bangpakong River about 39 miles (62.4 km) east by south of Bangkok where the water was quite fresh (this river enters the Gulf of Thailand at the NE “corner”) ( Smith, 1945).

The only recently collected specimens known have all come from peninsular Thailand and south Vietnam. The KUMF specimens came from the Bang Nara River, not far north of the border with Malaysia (unfortunately no habitat information was available). The Phuket specimens came from a small (0.1–1.5 m wide) muddy creek draining through tall mangrove forest into Klong Bang Sai (on the other side of which was an abandoned tin mining area). The substrate was sandy-mud to fine mud, with leaf litter, sticks and tiny burrows visible, and the creek was occupied by about 20 species of gobioids.

Remarks. – According to the original description, Smith (1931) had only one specimen, the holotype, which was eventually sent to the USNM (USNM 90316). However, Smith (1945) mentions that other specimens had since been collected from other parts of the Bangpakong River and he lists what he states are paratypes held at USNM (USNM 119593, which currently consists of three specimens, and USNM 119591, one specimen). The latter two lots of specimens cannot be paratypes, as Smith (1931) clearly stated that he was describing his new species and genus “... from a single specimen...”.

This species is the type of the genus Eugnathogobius . Smith (1945) considered that Eugnathogobius was related to Gnathogobius (a junior synonym), Mahidolia , Pseudogobiopsis and Waitea (the last a synonym of Oligolepis ), due to their greatly enlarged jaws. Mahidolia is a gobiine, while the others are gobionellines ( Birdsong et al. 1988; this paper). Koumans (1940) considered that E. microps was “Probably a good genus and species”.

Glossogobius mas Hora is possibly this species (type lost; see under Remarks for E. kabilia ). Hora (1923) states that his species has small eyes and a “deeply notched” tongue, but he does not indicate if there are scales on the nape. If material from the type locality is shown to be identical to E. microps , Hora’s name then has priority.

Figures

Fig. 11. Jaws and suspensoria of Eugnathogobius microps, male, ex NTM S.13953-013, Phuket, Thailand. Scale bar = 1 mm.

Fig. 12. Eugnathogobius microps papillae pattern. NTM S.13953-013, Klong Bang Sai, Phuket, Thailand. Scale bar = 1 mm.

Fig. 13. Eugnathogobius microps, 25.5 mm SL, NTM S.13953-013, Klong Bang Sai, Phuket, Thailand.

Fig. 23. Pseudogobiopsis festivus, new species, papillae pattern. 26 mm SL female, CMK 8401, Sungei Bejit, Sarawak: A, lateral view; B, dorsal view. Scale bar = 1 mm.

Fig. 18. Eugnathogobius siamensis, papillae pattern. Paratype, Vaimosa jurongensis, CAS 32983, 33.5 mm SL male, Jurong, Singapore. Scale bar = 1 mm.