Pseudogobius rhizophora, Larson & Hammer, 2021

Larson, Helen K. & Hammer, Michael P., 2021, A revision of the gobiid fish genus Pseudogobius (Teleostei, Gobiidae, Tridentigerinae), with description of seven new species from Australia and South-east Asia, Zootaxa 4961 (1), pp. 1-85 : 67-69

Pseudogobius rhizophora n. sp.

urn:lsid:zoobank.org:act:6626161E-CF15-40DC-9D53-B5A09A813A6A

Racing-stripe snubnose goby

Figs 1 , 26–27 , Tables 2–5, 19

Pseudogobius sp. 3—Larson 1996: 11 (Roper River; Nayarnpi Creek; Towns River); Larson 1997: 41 (West Alligator Head); Larson 1999a: 44 (Kakadu); Larson 1999b: 33 (Field Island); Larson 2000: 49 (Kakadu); Larson 2002: 40 (Sandfly Beach; Middle Beach; Pococks Beach); Larson et al. 2013: 206 (Roper River; Nayarnpi Creek; Towns River; West Alligator Head; Kakadu National Park; Field Island; Sandfly Beach; Middle Beach; Pococks Beach; Settlement Beach, Milingimbi); Hammer et al. 2021: 2 (northern Australia, Darwin and Maningrida [distinct mitochondrial DNA lineage]).

Material Examined. Holotype: NTM S.14028-020, 15 mm SL male, Nayarnpi Creek, Roper River , Northern Territory, Australia, HL 94-20, H.K. Larson and R. S. Williams, 10 September 1994 . Paratypes: NORTHERN TER- RITORY: NTM S.14028-024, 365(6–20), same data as holotype ; NTM S.10469-011, 262(7–17), Channel Island , mangrove creek at south end, H.K. Larson , R.S. Williams and A. Sim, 5 July 1982 ; NTM S.11360-010, 9(12–19), Darbilla Creek mangroves, Milingimbi , H.K. Larson, P. Horner , R. Johannes and Lyle , 23 July 1984 ; NTM S.13465- 005, 4(13–17), mouth of Blackmore River, M. Burke , 17 June 1991 . WESTERN AUSTRALIA: AMS I.25518-007, 5(16–18), West Creek at road crossing, Port Hedland, Western Australia, D.F. Hoese and D. Rennis , 18 September 1985 ; AMS I.25538-009, 6(13–15), Parry Creek, 7.5. km from road, Wyndham , Western Australia, D.F. Hoese and D. Rennis, 28 September 1985 . QUEENSLAND: NTM S.12869-004, 10(14–16), Embley River, Cape York, S. Blaber , 30 October 1990 .

Additional material (no data taken). NORTHERN TERRITORY: CSIRO H.8045-01, 3, west side Groote Eylandt , Northern Territory, S. Blaber, 21 October 1990 ; NTM S.14024-018, 6, Small Creek North Side, Roper River , HL 94-16, H.K. Larson and R. S. Williams, 8 September 1994 ; NTM S.14042-040, 22, Mangrove Creek at Mouth, Towns River , HL 94-35, H.K. Larson and R. S. Williams, 13 September 1994 ; NTM S.10798-036, 6, NW corner of Buchanan Island, Bathurst Island, HL 82-87, H.K. Larson, J. Randall and G. Cole , 18 November 1982 ; NTM S.15831-001, 2, Charles Darwin National Park, Darwin Harbour, E1-8, K. Metcalfe , 14 July 2003 ; AMS I.23936- 008, 1, East Arm boat ramp, Darwin Harbour, D. Rennis and R. Williams, D. Rennis and R. Williams , 3 August 1983 ; NTM S.13489-004, 1, Blackmore River Mouth, Middle Arm, Darwin Harbour , SITE 2 , M. Burke, 6 March 1992 ; NTM S.16164-011, 1, Ludmilla Creek, Darwin Harbour , HL 03-01, H.K. Larson and party, 3 July 2003 ; NTM S.18301-002, 9, East Arm boat ramp, Darwin Harbour, MH 19-03 , M. Hammer and M Borok, 21 February, 2019; NTM S.12446-009, 1, creek at south end Cadell Strait , Napier Peninsula , HL 88-8, H.K. Larson , 2 February 1988 ; NTM S.15915-010, 22, Field Island, Kakadu National Park , HL 04-25, H.K. Larson and party, 18 August 2004 . QUEENSLAND: AMS I.23277-014, 5, Mission River mouth, Wallaby Island, D. Hoese and D. Rennis , 9 October 1982 ; NTM S.12869-002, 3, Embley River, Cape York, S. Blaber , 30 October 1990 ; AMS I.23265-004, 4, Embley River, Weipa, D.F. Hoese and D. Rennis , October 1982 ; AMS I.22078-011, 4, Norman River, Karumba, D. Hoese and H. Larson , 28 September 1980 . WESTERN AUSTRALIA: WAM P.25472-003, 1, Derby, V. Semenuik , October 1975 ; AMS I.25522-004, 2, creek by caravan park, King Sound, Derby , Western Australia, D.F. Hoese and D. Rennis, 21 September 1985 .

Diagnosis. A small, strongly sexually dichromatic Pseudogobius with second dorsal rays I,7; anal rays I,6–7; pectoral rays 13–16; 16 segmented caudal rays in 9/7 pattern; lateral scales 25–28; TRB 8–9; predorsal scales 6–8; snout short and slightly pointed; opercle with 3 rows of cycloid scales, cheek naked; shoulder girdle with smooth edge or low angled bony flange; tongue short, tip blunt to bluntly rounded; outer row of teeth in upper jaw slender, slightly curved and pointed (may be slightly flattened); males with narrow black line along mid-side of body and dense black rounded spot at upper base of caudal fin, while females with broken dark brown line and a less pronounced black spot at upper base of caudal fin; known from mangrove creeks and muddy rocky reefs in northern Australia.

Description. Based on 35 specimens, 13–19.5 mm SL. An asterisk indicates the counts of the 15 mm SL male holotype ( Fig. 27D ).

First dorsal VI*; second dorsal always I,7*; anal I,6–7* (rarely I,6); pectoral rays 13–16 (usually 15*); segmented caudal rays 9/7, 8/7 once; branched caudal rays 6/6–8/7, usually 7/6 8/7; lateral scale count 25–28 (modally 26*); TRB 8–9* (modally 8); predorsal scale count 6–8 (modally 7*). Gill rakers on outer face of first arch tiny and pointed, 1+5 (1).

Body slender, compressed. Head slightly wider than deep, HL 24.1–28.1% SL (mean 26.1%). Depth at posterior preopercular margin 59.5–66.7 HL (mean 62.8%). Width at posterior preopercular margin 63.4–75.0% HL (mean 70.1%). Mouth small, subterminal, very slightly oblique, jaws reaching to below mid-eye in males and to anterior half of eye in females; upper jaw 28.6–43.9% HL (mean 34.8%); lips relatively thin, lower lip broadly fused to chin anteriorly. Eyes lateral, high on head, 28.2–35.1% HL (mean 31.7%). Snout short, rounded, 21.3–28.9% HL (mean 25.5%). Interorbital narrow, 10.3–19.4% HL (mean 16.0%). Body depth at anal origin 16.4–19.2% SL (mean 18.0%). Caudal peduncle compressed, length 25.9–30.8% SL (mean 29.1%). Caudal peduncle depth 11.3–28.9% SL (mean 17.7%).

First dorsal fin low, rounded to roughly triangular, second to third spines longest. Appressed first dorsal fin may just reach or fall short of first second dorsal fin element in adult males, fin falling well short of second dorsal fin in females; length 15.9–19.3% SL (mean 17.9%). Second dorsal spine length 11.6–15.6% SL (mean 14.0%). Third dorsal spine length 11.6–15.0% SL (mean 13.9%). Second dorsal and anal fins short, low, fins slightly pointed to rounded posteriorly with posteriormost rays longest, rays falling well short of caudal fin base when appressed. Pectoral fin oval, central rays longest, not quite reaching a vertical above anus, 17.3–24.8% SL (mean 21.2%). Pelvic fins short, rounded, not reaching anus, 15.0–20.7% SL (mean 18.3%). Caudal fin oval, rounded posteriorly, 25.1–31.7% SL (mean 27.8%).

Anterior nostril in short tube, oriented down over upper lip. Posterior nostril oval, with very low rim, placed at mid-level of eye. Gill opening narrow, extending length of pectoral fin base. Gill rakers on outer face of first arch tiny and pointed. Shoulder girdle with narrow smooth edge or with low angled bony flange. Tongue short, tip blunt to bluntly rounded. Upper jaw teeth in 2–3 rows, teeth in outermost row always largest, slender, slightly curved and pointed (may be slightly flattened), inner row teeth small and sharp. Lower jaw teeth in 2–3 rows, similar in size and shape to those of upper jaw but usually more upright.

Body scales ctenoid in wedge shape to below first dorsal fin or to close behind pectoral fin base, predorsal scales cycloid; pectoral fin base naked; opercle with three rows of cycloid scales; breast and belly naked or with cycloid scales (belly may have some ctenoid scales anteriorly). Lateral canals, pores and sensory papillae pattern as in Fig. 26 ; several specimens from Channel Island (Northern Territory) with separate interorbital canals (therefore two posterior interorbital pores present instead of one).

Coloration of preserved material. Males with head and body pale yellowish to yellowish brown, with scale margins narrowly outlined with brown, less defined on lower half of body ( Fig. 27 ). Head darker than body in mature males, with no distinctive spots or bars on side of head. Dark brown to blackish line running from above opercle along mid-side of body to end at hypural crease, where line broadens to become rounded blotch or narrow vertical bar along caudal base. Underside of head and breast dark brown; belly paler and may be unpigmented. First dorsal fin transparent with black line of variable width above base; fin margin transparent to greyish. Second dorsal fin transparent with grey or blackish band above base and scattered greyish blotches or streaks below margin. Anal fin plain brown to grey. Pectoral fins transparent with scattered grey speckles. Pelvic fins brown with translucent frenum and disc margin. Caudal fin transparent to greyish to dark grey, with translucent to whitish rear margin and characteristic round black spot near upper base of fin, often with short curved bar extending ventroposteriorly from it; may be second smaller dark spot anterior to black spot. When alive, black stripe along side may have scattered faintly iridescent blue or blue-green spots along it.

Females with head and body pale yellowish to whitish, with scale margins on dorsum outlined in brown or diffuse blackish, forming cross-hatched pattern; markings on lower half of body generally less distinct than on upper. Mid-side of body with broken brown line or series of brown elongate blotches; line may be partly replaced by diffuse X-shaped dark marks. Base of caudal fin with variable triangular to <-shaped brown blotch. Head plain brown; heavily pigmented females with dark brown line from front of eye to snout tip, covering nostrils. Underside of head and breast pale brown or unpigmented; belly pale. Unpaired fins similar to those in male but markings generally paler. Pectoral and pelvic fins translucent. Caudal fin transparent to pale greyish with round or oval dark brown spot at upper base, with whitish round blotch above and below dark spot; lowermost whitish blotch with brown margin ventroposteriorly.

Coloration of live specimens. Males and females sexually dichromatic ( Fig. 27 ). Males with head and body pale fawn to translucent pale brown, head darker brown in adults, scale margins on lower half of body thinly edged with dark brown, dorsum with about 7–8 irregular brown patches; narrow black line from mid-eye running along mid-side of body to end at caudal fin base. Indistinct blackish line may be present from front of eye angled down to front of snout. Lips dark brown. Iris golden. Peritoneum silvery white, visible through body wall. First dorsal fin translucent yellowish with faintly greyish margin and brownish stripe along base; second dorsal fin transparent with broken brownish strip along base and faint greyish speckling on distal half of fin; anal fin dusky grey with broad bright white margin; caudal fin translucent grey to dark grey, palest dorsally, with broad white margin, large black and bright blue blotch on upper part of fin close to base with short curved bar extending ventroposteriorly from it; pectoral fins transparent; pelvic fins dark brown to blackish with white to bluish white margin.

Females with head and body pale fawn to translucent pale brown, scale margins on body very thinly edged with brown, side of body with scattered irregular brown spots and blotches; dorsum with about 7–10 small irregular brown patches. Indistinct brownish line may be present from front of eye angled down to front of snout. Lips pale brown. Iris golden. Peritoneum silvery white ventrally and posteriorly, visible through body wall. Caudal fin transparent with blackish rounded spot on upper base of fin, with blackish curved band running ventrally from it and surrounding pale yellow blotch; pale yellow area present on base of fin above blackish round spot.

Comparisons. This species is not easily confused with other species of Pseudogobius due to its small size and strong sexual dichromatism, and the distinctive pattern on the caudal fin separates both sexes from all other species.

Distribution. Endemic to northern Australia, from Port Hedland, Western Australia to Weipa on western Cape York Peninsula, Queensland.

Ecology. Shallow-water estuarine to marine, found in mangrove creeks and muddy rocky reefs, at depths of 0–2 m. Typically co-occurs with P. aquilonius .

Etymology. This species is named rhizophora (as a noun in apposition) due to its preference for mangrove habitats (and the mangrove Rhizophora stylosa is the mangrove species found over a wide range of conditions in northern Australia).

Figures

FIGURE 1A. Distribution maps of species in the genus Pseudogobius, based upon material examined and inspected (circles) with the type localities indicated (squares).

FIGURE 26. Sensory pores and papilla rows in Pseudogobius rhizophora n. sp., female, NTM S.10469-011, Channel Island, Darwin, Northern Territory. Drawing by HKL.

FIGURE 27. Pseudogobius rhizophora n. sp., northern Australia, (A) captive male nuptial display, Channel Island, Darwin Harbour; (B) captive female, Channel Island, Darwin Harbour; (C) fresh male (upper) and female, NTM S.18301-002, from East Arm, Darwin Harbour; (D) preserved holotype, 15 mm SL male, NTM S.14028-020, Nayarnpi Creek, Roper River. Photos by MPH.