Trimma unisquame ( Gosline, 1959 )

Winterbottom, Richard & Hoese, Douglass F., 2015, A revision of the Australian species of Trimma (Actinopterygii, Gobiidae), with descriptions of six new species and redescriptions of twenty-three valid species, Zootaxa 3934 (1), pp. 1-102 : 90-92

Trimma unisquame ( Gosline, 1959)

Blackmargin Pygmygoby

Figs. 50–51 , Pl. 4 B

Hazeus unisquamis Gosline, 1959:70 (Oahu, Hawaii).

Trimma sp. A: Winterbottom, 1984:713 (Chagos Archipelago).

Trimma unisquamis: Randall, 2005:554 (photo from Hawaii); Bacchet et al., 2006:457 (Tahiti).

Material. Sixty-nine specimens, 9.1–19.3 mm SL, Comores, Western Indian Ocean to Easter Island, Eastern Pacific Ocean. This species has not been redescribed in any detail since its original description, so we provide fuller details of the material we have examined.

Australian material. Queensland: Boot Reef: NTM S.13615-007, (17), 14– 17 m. Holmes Reef: WAM P.29627-041, 2(15–15), 7– 8 m. Christmas Id: WAM P.26120-015, (18), 3–4 m; WAM P.26083-027, (14), 3– 6 m. Cocos (Keeling) Ids: WAM P.29926-023, 2(10–11), 20– 25 m.

Other material: Chagos Archipelago: ROM 41473, (11.6). Comores: Anjouan Id: ROM 59809, 5(9–14); ROM 59810, 2(13–14); ROM 59811, (10). Cook Ids: Rarotonga: BPBM 13963, 2(15–15); ROM 38122, 2(15–17). Easter Id: BPBM 31957, 2(15–19). Fiji: Great Astrolabe Reef: ROM 45959, (15); ROM 45960, (14); ROM 54446, (14). Lau Group: USNM 243044, 16(10–16); USNM 243194, 2(13–14); USNM 303422, (11); USNM 41717, (10). Hawaii: USNM 175009, (18), holotype; BPBM 28735, 7(10–14). Johnston Id: BPBM 22630, 3(16–18). Micronesia: Ifaluk Atoll: CAS 59883, (15). Society Ids: Moorea: AMNH 30923, (19); AMS I.21651–036, 5(12–15); ROM 59418, 2(12–13); ROM 59755, 1 (15); ROM 59756, 3(13–15); ROM 59757, (11). Tahiti: BPBM 9415, (16).

Diagnosis. A species of Trimma with 7 dorsal- and anal-fin rays; 18–20 pectoral-fin rays with the lower 6–9 thickened relative to the upper rays; fifth pelvic-fin ray as long or slightly longer than fourth; a pelvic fraenum and full basal membrane; a row of small, vertically-oriented, ctenoid scales along the median dorsal half of each orbital rim; first dorsal fin with a black margin; and prepelvic region scaleless.

Description. The description is based on all specimens that were in reasonable enough condition for the characters to be recorded (thus the number of specimens used for each character varies) irrespective of the collection locality. Dorsal fins VI + I 7, no spines elongated, third and fourth reaching to first element of seconddorsal fin when adpressed, first ray branched or unbranched, all remaining rays branched; anal fin I 7 (once I 6), all rays unbranched except for posterior half of last ray, which may be branched; pectoral-fin rays 18–20 (mean = 19.0), dorsalmost 2–3 rays unbranched, followed by 6–10 branched rays (lowest numbers in smaller specimens) and 6–9 unbranched and slightly thickened rays; pelvic fin I 5, first four rays branched 2–4 times sequentially, fifth ray slightly longer than fourth and reaching to between urogenital papilla and anal-fin origin posteriorly, branched 3 times dichotomously (i.e. eight terminal tips); full basal membrane and complete fraenum. Lateral scales 23 (once 24); transverse scales 7 (once 6.5); up to 5 horizontal rows of ctenoid scales present on opercle, with 1–5 scales per row (higher numbers dorsally, lower numbers ventrally); usually a single cycloid scale on cheek; medial bony margin of upper half of orbital trenches with about 10, vertical, small ctenoid scales in row on each side from posterior nares to sphenotic area; 5–10 cycloid predorsal scales in midline (lower numbers in smaller specimens) which may reach interorbital trough in larger specimens but end anteriorly at level of posterior margin of eye in smaller specimens; 3–4 cycloid scales in vertical row on base of pectoral fin, ventral one-fifth of pectoral-fin base and breast scaleless, remainder of body covered with ctenoid scales. Teeth in outer row of upper jaw and inner and outer rows of lower jaw of spaced, enlarged, curved canines, with irregular rows of small conical teeth in between. Tongue truncate, two-thirds pupil diameter in width. Gill opening extending to anterior margin of pupil; outer rakers of first gill arch 1–4 + 14–16. Nasal apparatus confined to posterior half of snout, anterior and posterior nares in short tubes, posterior margin of posterior tube adnate to anterior margin of fleshy orbit. Interorbital trough well-developed, posterodorsal trough weakly developed or absent; bony interorbital equal to about one quarter pupil diameter, epaxial musculature just to or not quite reaching level of posterior margin of eye in dorsal midline. Vertebral pattern essentially Type B, but differs from usual arrangement in having only one haemal canal opening in first caudal vertebra of single specimen examined.

Colour pattern. Freshly collected. Based on 35 mm colour slides of 8 specimens from the Comores, Chagos (illustrated in colour by Winterbottom, 1984, fig. 10), Fiji (x 2 – see Fig. 51 ), Cook Islands, Society Islands (x 2) and Easter Island. Head and body suffused with yellow, orange or red pigment, more intense anteriorly, especially on head. Suffusion overlain by numerous greyish saddles and blotches, primarily dorsally located, and made up of mixture of melanophores, brown chromatophores and iridocytes. Some scale margins, especially dorsally, rimmed with melanophores. Light bar on cheek beneath anterior half of pupil, another at vertical limb of preopercle, faint (Indo-west Pacific) or well-developed dark (Pacific plate) bar across margins of hypurals. Margin of both dorsal fins black, fin rays yellow to red, iris red with narrow golden rim adjacent to pupil. Live specimen from Hawaii (Pl. 4 B) with brown body and grey areas white, bar at vertical limb of preopercle faint, caudal bar more of an ovoid blotch.

Preserved. Background pale straw-yellow, only melanophores and brown chromatophores visible, saddles and blotches less evident.

Etymology. From “ unisquame = (L.) one scale, in reference to the single cheek scale.” ( Gosline 1959:71). The etymology as given in the original description implies that Gosline intended the specific name to be a noun in apposition, however, the Latin noun for scale is squama and squamis literally means with scale, indicating an adjective. The word therefore takes the neuter adjectival ending, and Trimma unisquame is used here.

Distribution. The species is rather rare in collections, and has primarily been collected south of the equator. The exceptions are the samples from Hawaii (the type locality) and the single collection from Ifaluk Atoll in Micronesia ( Fig. 50 ).

Comparisons. Only one other species of Trimma ( T. fraena Winterbottom, 1984 ) possesses a pelvic fraenum. This species, and all others in the genus, lack the deep, scale-lined interorbital trench, and almost all (except T. corallinum and T. omanensis ) also possess prepelvic (= breast) scales. The presence of 7 dorsal- and 6–7 anal-fin rays is also rarely encountered in Trimma .

No specimens were available for genetic analysis.

Discussion. This is the most widely distributed species of Trimma , but is seldom taken in any significant numbers. Some variation is apparent, with the dark vertical bar across the end of the hypural plate being well developed in Pacific plate populations, but poorly developed in populations from Fiji westward. A different pattern of variation may occur in pectoral-fin ray number, where Indian Ocean specimens have a mean of 18.4 (n = 9) as opposed to a mean of 19.2 (n = 22) for west-central Pacific specimens. Given the non-congruence of these two variation patterns, no further systematic action is planned at this time.

The species is known from depths of 3– 27 m. In Australia it is known from only from reefs on the outer edge of the northern Great Barrier Reef and reefs of the Coral Sea east of the Great Barrier Reef. Trimma unisquame has been informally referred to as Trimma DFH sp. 45 or RW sp. A.

Figures

FIGURE 50. Distribution map for Trimma tevegae (solid circles with white stars) and T. unisquame (solid squares with white circles). A hollow square with an X indicates localities at which both species occur.

FIGURE 51. Trimma unisquame, 13.5 mm SL female, ROM 45960, Fiji. Photo by R. Winterbottom.