Eugnathogobius indicus, Larson, 2009

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 : 133-135

Eugnathogobius indicus new species

( Figs 3 , 4 ; Tables 3–7)

Material examined. – HOLOTYPE – AMS I.23623-001, 27 mm SL female, Bazaruto Island , off Inhossoro, Mozambique, 4 May 1972 . PARATYPES – NTM S. 16251-001, 1(25.0), pools at end of mangrove creek, Gazi Bay , Kenya, H. Coehne, Jul.-Aug.1993 ; USNM 316139 , 6 (13.5–15.5), in well at trail marker 37, Grand Terre , Aldabra Atoll, Seychelles, J. Louton, 3 Jun.1990 ; RUSI 5461 , 8 (13.5–33.0), Bazaruto , Mozambique, 4 May 1972 ; AMS I.23623-002, 1(23), same data as holotype .

Diagnosis. – Small, slender-bodied Eugnathogobius ; first dorsal fin VI; second dorsal rays I,7–8, modally I,7; anal rays I,6–8, modally I,7; pectoral rays 15–17, modally 16; longitudinal scales 32–41; TRB 10-13; headpores absent; predorsal scales 14–20; scales on body small, mostly ctenoid; gill opening restricted to just under opercle; colour pale yellowish with dark scale margins in network pattern and variably distinct dark stripe along mid-side of body; known only from Kenya, Mozambique and Seychelles, in estuarine and freshwater habitats.

Description. – Based on 16 specimens, 15–33 mm SL. Counts of female holotype ( Fig. 3 ) indicated by asterisk.

First dorsal VI; second dorsal I,7–8 (mean I,7*); anal I,6-8 (mean I,7*), pectoral rays 15–17 (mean 16*), segmented caudal rays 15–17 (mean 16*); caudal ray pattern modally 9/7*; branched caudal rays 12–16 (mean 14, 15 in holotype); unsegmented (procurrent) caudal rays 6/5 (in 1), 6/6 (in holotype), 7/7 (in 2); longitudinal scale count 32–41 (mean 35*); TRB 10*-13 (mean 11); predorsal scale count 14–20 (mean 11, 16 in holotype); circumpeduncular scales 12–14* (mean 13). Gill rakers on outer face of first arch 2+7 (in 1), 3+5 (in 1), 3+7 (in 2), 3+8 (in 2), 4+6 (in 1). Pterygiophore formula 3-12210* (in six). Vertebrae 10+16* (in 8). Neural spine of first few vertebrae narrow, pointed. Two* (in 8) epurals. Two* (in 7) or three (in 1) anal pterygiophores before haemal spine of first caudal vertebra.

Body very slender and compressed, less so anteriorly; head broad and somewhat depressed. Body depth at anal fin origin 14.4–18.7% (mean 16.5%) in SL. Head rounded, always wider than deep, HL 26.4–31.1% (mean 28.7%) of SL. Depth at posterior preopercular margin 53.6–61.9% (mean 57.0%) of HL. Width at posterior preopercular margin 68.1–81.0% (mean 74.6%) of HL. Mouth terminal, slightly oblique, forming angle of about 15° with body axis; jaws not greatly enlarged in males, reaching to just below anterior half of eye in large adults or to just below anterior margin of eye in male specimens less than 25 mm SL. Lips smooth, with fine fleshy fimbriae present on inner edges of lips; lower lip free at sides, fused across front. Upper jaw 32.6–47.0% (mean 37.2% in males, 35.1% in females) of HL. Eyes relatively small, dorsolateral, high on head, top forming part of dorsal profile, 21.7–30.3% (mean 25.3%) of HL. Snout short, flattened, rounded in dorsal view, 22.7–30.0% (mean 26%) of HL. Interorbital moderate to fairly wide, usually flat, 14.5–25.0% (mean 20.5%) of HL. Caudal peduncle quite compressed, length 21.9–28.9% (mean 26.7%) of SL. Caudal peduncle depth 11.3–12.9% (mean 12.1%) of SL.

First dorsal fin low, third spine nearly always longest; spines slightly longer in males than females; tips of spines just reaching past first and second fin element of second dorsal fin (in 33 mm SL specimen); in most specimens, first dorsal fin spines falling short of second dorsal fin, or just reach second dorsal fin spine base. Third dorsal spine length 11.5–19.7% (mean 13.8%) of SL. Second dorsal and anal fins low, shortbased, posteriormost rays longest, in most specimens, fin rays falling short of caudal fin base when depressed (as in holotype); in 33 mm SL male, rays reaching to caudal fin procurrent rays. Pectoral fin moderately broad to slightly pointed (tips variably damaged in many specimens), central rays longest, 20.3–25.5% (mean 22.4%) of SL; rays usually all branched. Pelvic fins rounded to somewhat oval, often cup-like, nearly reaching anus, 18.4–22.2% (mean 20.3%) of SL. Caudal fin short, rounded to truncate, 24.6–30.3% (mean 27.3%) of SL.

No mental fraenum or fold, chin smooth. Anterior nostril tubular, placed at edge of upper lip, tube short, oriented down and forward, preorbital usually curved to accommodate nostril. Posterior nostril small and rounded, placed very close to upper front margin of eye. Gill opening usually extending forward to just under opercle. Inner edge of pectoral girdle smooth with very low, bony ridge on anterior face of cleithrum, usually forming distinct thin flange of bone, with two to three small fleshy knobs. Gill rakers on outer face of first arch greatly reduced, very short fleshy knobs, largest raker by angle of arch; rakers on inner face of first arch also short and stubby; inner rakers on other arches slightly longer and more slender than first arch inner rakers. Tongue reduced to nearly absent, tip blunt. Outer teeth across front of upper jaw sharp and curved, larger (but not greatly so) than inner row teeth; behind this row, two to three rows of very small, pointed teeth; one or two rows of small pointed teeth at side of jaw (outer row teeth not enlarged in males). Lower jaw with three or four rows of small curved sharp teeth across front, inner rows all pointing inward; usually one or two rows of teeth at side of jaw.

Predorsal scales very small and cycloid, reaching to, or just anterior to, posterior preopercular margin. Operculum with patch of small cycloid scales on upper third to half; sometimes entire operculum scaled. Cheek always naked. Pectoral base naked. Prepelvic area naked. Belly with cycloid scales; ctenoid scales may be present anteriorly, close by pelvic fin base or up to anterior third of belly with ctenoid scales. Scales on body small, those on caudal peduncle tending to be larger. Ctenoid scales on side of body extending anteriorly to up behind pectoral fin; small specimens from Aldabra with only few scales anteriorly.

Genital papilla in male slender and flattened, with pointed tip; genital papilla in female short and cylindrical to rounded and bulbous.

Head pores absent.

Sensory papillae pattern longitudinal. Two s rows present on snout, of one papilla each. Cheek rows b and d composed of small closely spaced papillae; rows a, c and cp of few large widely spaced papillae. Mental f rows consisting of two pairs of papillae.

Colouration of fresh material. – No information available.

Colouration of preserved material. – Based on holotype and two largest paratypes ( Figs. 3 , 4 ); most specimens faded. Head and body light yellowish, with scale margins on most of body, especially upper half, narrowly outlined with light brown, side of body with small cross-hatched brownish blotches, short bars and X-shaped marks, forming lateral stripe or series of blotches linked by dusky midlateral line; blotch at caudal base may be darkest. Holotype most heavily pigmented specimen, with about seven indistinct brownish saddles crossing dorsum, blending with dark scale margins ( Kenya specimen has remnants of these saddles).

Head and nape speckled with pale brown dorsally, pigment evenly distributed or forming faint spots or diffuse blotches. Side of head with several pale brownish irregular blotches, opercle with one or two darker brown horizontal bars or blotches, indistinct brownish bars from eye to snout tip and lower jaw visible on Kenyan specimen. Lips plain, pale whitish yellow. Underside of head pale (diffuse brownish band crossing isthmus behind chin in Kenyan specimen). Breast pale yellowish-white. Pectoral base pale with short brown horizontal bar or spot across upper half. Belly whitish.

First dorsal fin transparent to light brown, outer half dusky to brown; or with lower third of fin translucent and outer portion light to dark brown. Second dorsal fin translucent with scattered pale brown pigment, which may form row of dark blotches. Anal fin transparent to translucent yellowish. Caudal fin translucent yellowish, faintly spotted with brown; narrow brown vertical bar along hypural crease; just behind vertical bar, a pair of faint brownish spots. Pectoral fins translucent, sometimes with light brown fin rays. Pelvic fins plain, translucent.

Comparisons. – This species resembles the two other dwarf slender species ( E. polylepis and E. stictos , new species) in its general morphology but differs in usually having second dorsal and anal fin ray counts of I,7 (vs. usually I,8) and its lower lateral scale counts (32–41 vs. 48–63).

Distribution. – Restricted to the Indian Ocean, to coasts of Mozambique and Kenya, and Aldabra Atoll in the Seychelles.

Etymology. – From the Latin indicus , referring to India; in this case the Indian Ocean, where this species occurs.

Ecology. – Limited information is available; the species appears to be marine to estuarine in habitat. The specimens from the freshwater well on Aldabra are intriguing in their isolation.

Figures

Fig. 3. Eugnathogobius indicus, new species, holotype, 27 mm SL female, AMS I.23623-001, Bazaruto Island, Mozambique.

Fig. 4. Eugnathogobius indicus, new species, paratype, 14 mm SL, male, USNM 316139, Grande Terre, Aldabra Atoll, Seychelles.