Eugnathogobius stictos, 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 : 153-154

Eugnathogobius stictos new species

( Fig. 21 ; Tables 3–6, 12)

Calamiana sp. nov. 3 – Larson 2001: 62.

Type Material. – HOLOTYPE – NTM S.14287-001, 22 mm SL male, mouth of East Alligator River , Northern Territory, Australia, beam trawl, T. Davis, Apr.1979 . PARATYPES - AMS I.32051-032, 12(12.5–22), same data as holotype ; NTM S.14287-002, 2(20–20.5), same data as holotype .

Diagnosis. – Small (to 22 mm SL), slender-bodied Eugnathogobius ; first dorsal fin always V; second dorsal rays I,8–9; anal rays I,7–8; pectoral rays 14–18; longitudinal scales 48–61; TRB 15-22; predorsal scales absent; headpores absent; scales on body mostly cycloid, weak, ctenoid scales present on caudal peduncle; gill opening restricted to pectoral base; colour pale yellowish with small brown to blackish spots and flecks along upper sides of body and caudal fin dusky with vertical bars; known only from the East Alligator River estuary, Northern Territory.

Description. – Based on 14 specimens, 16.5–22 mm SL. Counts of holotype ( Fig. 21 ) indicated by asterisk.

First dorsal V* (13), VI (1); second dorsal I,8–9 (mean I,8*); anal I,7–8 (mean I,8*), pectoral rays 14–18 (mean 16, holotype with 18 on right, 17 on left), segmented caudal rays 13–16 (mean 16*); caudal ray pattern modally 9/7*; branched caudal rays 13–16 (mean 15*); unsegmented (procurrent) caudal rays 8/7 (in one); longitudinal scale count 48–61 (mean 54, 59 in holotype); TRB 15–22 (mean 18*); predorsal scales absent; circumpeduncular scales 18–25 (mean 22, 21 in holotype). Gill rakers on outer face of first arch 2+6 to 3+7 (modally 3+7). Pterygiophore formula 3-12210 (in one). Vertebrae 10+16 (in one). Neural spine of second vertebra blunted at tip, other spines narrow, pointed (in one). Two epurals (in one). Two (in one) anal pterygiophores before haemal spine of first caudal vertebra. Metapterygoid broad, with wide bridge overlapping quadrate; palatine slender; pterygoid short and stout. Upper ceratobranchial broad, pierced by relatively large holes, teeth long and robust. Scapula unossified. Four ossified gill rakers.

Body compressed, less so anteriorly; ripe females almost cylindrical anteriorly. Body depth at anal fin origin 15.3– 18.0% (mean 16.5%) of SL. Head rounded, somewhat depressed, wider than deep, but not greatly so, HL 25.9– 27.3% (mean 26.6%) of SL. Depth at posterior preopercular margin 53.3–68.8% (mean 61.4%) of HL. Width at posterior preopercular margin 64.4–77.1% (mean 73.4%) of HL. Mouth terminal, oblique, forming angle of about 25–35° with body axis; jaws reaching to below middle of eye in mature males and to below front half of eye in females and small males (to below mid-eye in holotype). Lips smooth, without fleshy fimbriae present on inner edges of lips; lower lip free at sides, fused across chin. Upper jaw 37.8–47.2% (mean 35.0% in females, 42.2% in males) of HL. Eyes relatively small, dorsolateral, high on head, forming part of dorsal profile, 22.9–29.1% (mean 25.5%) of HL. Snout flattened to rounded, blunt when viewed from above, 24.4–30.2% (mean 26.5%) of HL. Interorbital moderate to narrow, flat, 13.3–23.5% (mean 21.9% in females, 18.0% in males) of HL. Caudal peduncle compressed, length 23.5–26.5% (mean 24.5%) of SL. Caudal peduncle depth 10.8–13.7% (mean 12.1%) of SL.

First dorsal fin very low, rounded, tips of spines free, second or third spines longest or subequal; spines falling short of second dorsal fin origin when depressed. First dorsal spine length 10.0% of SL in one specimen. Second dorsal spine length 7.0–11.4% (mean 9.2%) of SL. Third dorsal spine length 7.0–11.4% (mean 8.5%) of SL. Second dorsal and anal fins low, pointed posteriorly, posteriormost rays longer than anterior rays, rays not reaching caudal fin base when depressed. Pectoral fin broad, rounded, central rays longest, 18.2–21.2% (mean 19.8%) of SL; rays all branched but for uppermost ray (usually unbranched). Pelvic fins short, oval, sometimes cup-like, reaching half or less the distance to anus, 14.1–17.5% (mean 15.1%) of SL. Caudal fin relatively long, rounded posteriorly, 24.1–29.1% (mean 26.7%) of SL.

No mental fraenum, chin smooth, flat. Anterior nostril in short tube, at edge of upper lip, tube oriented down and forward, preorbital curved forward to accommodate nostril. Posterior nostril oval, placed close to front centre margin of eye. Gill opening restricted to pectoral base, occasionally extending forward to just under opercle. Inner edge of pectoral girdle smooth with thick fleshy ridge on anterior edge of cleithrum, ridge occasionally bumpy, usually smooth. Gill rakers on outer face of first arch very short and unspined, most rakers similar in length; rakers on inner face of first arch also stubby; inner rakers on other arches slightly longer than first arch inner rakers. Tongue tip blunt to bluntly rounded; absent in two specimens. Outer teeth in upper jaw largest, stout and curved, one or two rows of small sharp teeth behind this row (outer row teeth slightly larger in males); one row of small teeth at side of jaw. Lower jaw with two or three rows of small, curved, pointed teeth across front; usually only one row of teeth at side of jaw.

Predorsal scales absent in all specimens. Body scales mostly cycloid, thin, difficult to see, extending anteriorly to over pectoral base. Small patch of weakly ctenoid scales behind pectoral fin in seven specimens, remainder with all cycloid scales; patch of distinctly ctenoid scales at base of caudal fin, covering approximately posteriormost third (or less) of caudal peduncle. Operculum with few small cycloid scales on upper half; scales often obscured by mucous coat. Cheek always naked. Pectoral base, breast and belly naked.

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

Head pores absent.

Sensory papillae pattern longitudinal, almost identical to E. polylepis ( Fig. 15 ). Two s rows present on snout, of one papilla each; rows p, c and cp reduced, papillae few and widely spaced. Mental f row of two pairs of papillae.

Colouration of fresh material. – No information available.

Colouration of preserved material. – Head and body pale yellowish, paler ventrally, with light brownish fine speckling; cheek with darker speckling ( Fig. 21 ). Underside of head and branchiostegal membranes brown in males; in females, brown branchiostegal membranes contrasting with pale underside of head. Most conspicuous markings are dark brown to blackish small spots, flecks and short streaks scattered over upper half of body, in some specimens, spots roughly forming two rows; markings sometimes forming about 12 indistinct blackish bars or blotches crossing dorsal midline.

In males, both dorsal fins plain dusky brownish with brown streak at base of first few fin rays; females with dorsal fins translucent with brownish speckling and short streaks. Anal fin dusky brownish with translucent to whitish margin. Caudal fin dusky to light brown with translucent margin on rear edge of fin and four to seven short, vertically oriented rows of brown spots and short streaks. Pectoral fins pale, rays outlined in light brown. Pelvic fins, including fraenum, pale to light brown. Males more intensely coloured than females; can be quickly distinguished by dark dorsal and anal fins.

Comparisons. – This species is most similar to E. polylepis (see Comparisons for that species).

Distribution. – Specimens are known so far only from one locality, the East Alligator River estuary, Northern Territory. Recent beam trawl surveys in the area have not obtained additional specimens, but it is likely the exact identical habitat was not sampled ( Larson, 1999a, b, 2000, 2002).

Ecology. – Specimens were obtained by 1 mm mesh beamtrawl, from muddy substrate.

Etymology. – From the Greek stiktos, meaning spotted or dappled, in reference to the fine black spots on the body.

Figures

Fig. 21. Eugnathogobius stictos, new species, holotype, male, 22 mm SL, NTM S.14287-001, East Alligator River, Northern Territory, Australia.

Fig. 15. Eugnathogobius polylepis, sensory papillae. NTM S.10419-007, Elizabeth River, Northern Territory, Australia. Scale bar = 1 mm.