Trimma insularum, Winterbottom, Richard & Hoese, Douglass F., 2015

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 : 36-39

Trimma insularum sp. nov.

Cocos Pygmygoby

Figs. 17–18 , Pl. 2 A

No published names apply to this species.

Material. All specimens collected at the Cocos (Keeling) Islands in the eastern Indian Ocean, and all show evidence of fairly extensive net abrasion, making scale counts very difficult (and possibly inaccurate).

Holotype. ROM 82970, (ex-ANSP 134898), 23.9 mm SL male, tidal channel and adjacent sandy area at south end of Direction Id, (12°05'35"S, 96°53'10"E), 1.5–5 m, Smith-Vaniz & Colin, 29 Mar. 1974.

Paratypes. ANSP 134895, 39(10.7–27.0), lagoon about half distance between West Id pier and Direction Id, (12°07'15"S, 96°51'15"E), 7.5 m, Smith-Vaniz et al., 28 Feb.1974. Direction Id: ANSP 134888, 34(14.8–24.6), patch reef in lagoon about 2 km SW of island, (12°06'30"S, 96°52'10"), 7.5 m, Smith-Vaniz et al., 2 Mar. 1974; ROM 82962 (ex-ANSP 134898), 11(18.8–28.2), and ANSP 134962, 1 (13.8), collected with the holotype. Horsburgh Id: WAM P.29906.016, 8(15.8–23.8), (12°05'S, 96°50'E), 20–31 m, Allen, 2 Feb. 1989; ANSP 134893, 6(17.2–23.7), about 1.2 km SSE of Possession Point, patch reefs inside barrier reef, (12°05'35"S, 96°50'55"E), 1–2 m, Smith-Vaniz et al., 25 Feb.1974; WAM P.29919.008, 32(12.4–24.2), (12°05'S, 96°51'E), 14–15 m, Allen, 20 Feb. 1989. North Keeling Atoll: AMS I.28993-019, 13(15-25), W side near Wreck Point (11°49'S 096° 49'E), G. Allen, 25 Feb 1989; WAM P.29910.023, 13(11.8–21.5), drop-off on middle of W side of island, (11°50'S, 96°49'E), 20–30 m, Allen, 11 Feb. 989; WAM P.29915.017, 42(10.7–21.7), landing place on W side of island, (11°50'S, 96°49'E), 20–25 m, Allen, 17 Feb. 1989; WAM P.29926.024, 20(11.5–22.6), (11°49'S, 96°49'E), 20–25 m, Allen, 23 Feb. 1989. Prison Id: ANSP 134892, 15(18.1–26.2), large coral head in lagoon, south side of islands, (12°06'20"S, 96°52'30"E), 5–6 m, Smith-Vaniz et al., 7 Mar. 1974. Turk Reef: ANSP 134889, (21.8), on drop-off to deep water at landing site on west shore, (11°49'40"S, 96°49'12"E), 6–12 m, Colin & Chapman, 6 Mar. 1974; ROM 1799CS (ex-ANSP 134891), 6(11.6–24.7, C&S), (12°06'30"S, 96°49'35"E), 3–12 m, Smith-Vaniz et al., 5 Mar. 1974; ANSP 134896, 10(14.4–22.2), on drop-off, along reef face and cave near base of reef drop-off, (12°06'30"S, 96°49'35"E), 45–49 m, Smith-Vaniz et al., 8 Mar. 1974; WAM P.29912.017, 32(10.7–21.2), (12°07'S, 96°50'E), 12–14 m, Allen, 13 Feb. 1989. West Id: ANSP 134890, (22.7), off north end outside barrier reef, (12°07'45"S, 96°48'55"E), 9 m, Smith-Vaniz et al., 28 Feb. 1974; ANSP 134897, 5(17.8–20.2), north end, outside barrier reef on sloping bottom, (12°08'00"S, 96°48'50"E), 14–18 m, Smith-Vaniz et al., 25 Feb. 1974.

Diagnosis. A species of Trimma with a vertically-sided, ‘U’-shaped interorbital trench and well developed postorbital trench, scales centred on the predorsal midline usually absent (although there may be 1–3 scales anteriorly in the midline, with a narrowly triangular naked area in front of the first dorsal spine); second dorsal spine elongated in adults (> 20 mm SL), and may reach posteriorly to the dorsal procurrent caudal fin rays; third spine somewhat elongated, often extending beyond the spine of the second dorsal fin; usually 10 dorsal, 9 anal and 17–19 pectoral-fin rays, the latter with 5–12 branched rays at the middle of the fin, fifth pelvic ray usually branched once and about half the length of the fourth (47–64%); 18–20 total gill rakers on the first gill arch; and bony interorbital width less than half pupil-diameter. When freshly collected, this species is immediately distinguishable from all other described species of Trimma by the broad oblique yellow stripe across the cheek ( Fig. 17 ).

Description. Based on 20 specimens from ANSP 134892, 3(20.4–25.8), ROM 1799CS, 6(12.6–24.8); ROM 82970 (23.9, holotype), and ROM 82962, 10(20.4–25.8), all collected at Cocos (Keeling) Islands. Dorsal fins VI + I 9– 10 (mean = 9.8), second spine longest and reaching to between base of second ray of D2 and end of peduncle when adpressed, third spine a little elongated, reaching posteriorly to between bases of first to sixth rays of second dorsal fin, usually first ray of second dorsal fin unbranched, (85%, in one specimen first two rays unbranched), posterior element of last dorsal ray unbranched, longest ray (penultimate or ultimate) reaching posteriorly beyond mid-peduncle; anal fin I 9, first and sometimes second ray unbranched, as is posterior element of last ray, which reaches posteriorly beyond mid-peduncle; pectoral fin 17 –19 (mean = 17.8, once 16), 3– 4 –6 dorsal and 2– 6 –8 ventral rays unbranched, fin reaching posteriorly to a point above urogenital papilla to anal spine; pelvic fin I 5, first four rays with one sequential branch, fifth ray usually branched once dichotomously (unbranched in 5) and 47– 60 –64% the length of fourth (mean = 54.7, n = 18), fourth ray reaching posteriorly to a point between bases of first to fourth anal ray; no fraenum; basal membrane vestigial (<5% length of fourth ray) or absent. Lateral scales 23– 25 (mean = 23.8, n = 14); transverse scales 7– 8 (mean = 7.3, n = 12); predorsal scales usually absent in midline, but 2–3 scales may partially cross midline anteriorly (n = 3), always a narrow triangular naked area in front of dorsal fin origin; scales extending anteriorly on sides of nape to just behind eye, scales on cheek apparently absent, opercle usually scaleless but may have a single cycloid scale dorsally (n = 3) pectoral-fin base margined posteriorly with a vertical row of 4– 5 scales, scales anterior to pelvic fin 6 –7 (mean = 6.7, n = 12), scales on pectoral-fin base, breast, anterior midline of belly and anterior nape cycloid, others ctenoid. Upper jaw teeth with a full outer row of evenly spaced, curved, enlarged canines which decrease in both size and spacing posteriorly, an inner row of similar teeth but about 3/4 size of outer row, ending above bend of dentary, 2–3 irregular rows of small conical teeth between these, curved near their tips, and grading to a single row on coronoid process of dentary. Lower jaw teeth with an outer row of about four evenly spaced, curved, enlarged canines ending at bend of dentary, an inner row of similar, slightly smaller teeth which decrease in size posteriorly and end at coronoid process, 2–3 irregular rows of small conical teeth between these, curved near their tips, and grading to a single row on coronoid process of dentary. Tongue truncately rounded, often with a slight central pointed tip. Gill opening extends anteroventrally to below mid-pupil; outer gill rakers on first gill arch 3– 4 –5 (mean = 3.8) + 15 –16 (mean = 15.3), total rakers 18– 19 –20 (mean = 19.2, n = 18). Anterior nares a short, sometimes broad tube, separated from upper lip by its width, post nares a large raised pore, separated from eye by its width. Bony interorbital width 28– 33 –45% of pupil diameter in width (mean 34.15, n = 12), interorbital with a well-developed ‘U’-shaped interorbital trench, postorbital trench well developed, narrow, also with vertical sides; epaxialis reaching anteriorly in dorsal midline to above posterior margin of pupil. Abdominal/caudal vertebral transition Type B.

Colour pattern. Freshly collected, from images of four specimens photographed by G. R. Allen ( Fig. 17 ). Background colour off-white to pale pink. Cheek with half-pupil width yellow stripe passing posterodorsally from distal tip of maxilla and lower jaw to midregion of dorsal margin of opercle, bordered dorsally by darker pink. Tapering, posteriorly-directed yellow stripe from behind mid-orbit along temporal groove to posterior margin of opercle, where it may hook anteroventrally along dorsal half of posterior margin of that bone. Round to laterally ovoid pupil-diameter yellow spot on posteroventral margin of cheek at bend of preopercle and another, similar but smaller spot over subopercle/interopercle abutting against posterior margin of preopercle. Half to full pupil diameter width stripe from midregion of upper lip to anterodorsal margin of eye. Iris with narrow red rim around margin of pupil, primarily yellow with reddish mottling below dorsal margin of pupil and purple above it. Proximal vertical region of pectoral-fin base orange or with diffuse large ventral yellow blotch. Two small yellow saddles over dorsum, equidistant from each other, first just behind posterior margin of eye, second just anterior to origin of first dorsal fin. Scale pockets of body outlined with mix of melanophores and red chromatophores. Variable number of diffuse yellow to orange spots present at ventral margins of second scale row below dorsal fins; series of similarly-coloured diffuse bars, about eye diameter in height and half pupil-diameter in width, along midlateral scale row; body below this with variable yellow to red mottling and spots. First dorsal fin with small yellow to orange spots on spines about half pupil-diameter above fin base, may be similar spots above this, especially posteriorly in fin. Second dorsal fin with similar yellow to orange spots, which may be arranged in vague oblique or horizontal rows, often alternating between adjacent fin rays. Fin membranes with scattered iridocytes. Anal fin with white distal margin bordered proximally by diffuse yellow to orange stripe; bases of alternate fin rays may exhibit yellow spots. Caudal fin with diffuse yellow to orange spots about half pupil-diameter in size, mostly in basal half of fin, membranes with scattered chromatophores and iridocytes, which latter may be concentrated in dorsal and ventral leading edges of fin. Live (based on an image by T. Uno, Pl. 2 A): Background colour orange-red with irregular, diffuse grey bars on body; occipital region mainly grey. Cheek red grading to yellow ventrally, with half pupil-diameter, greyish oblique stripe from upper opercle to distal tip of maxilla, passing immediately below eye, and continuing anteroventrally across lower jaw just ventral to lower lip. Another such stripe, but more diffuse, from angle of preopercle to point of articulation of lower jaw with suspensorium. Both stripes yellow in freshly collected material. Thin, faint grey outline along ventral margin of interopercle. Posterior snout and interorbital region with about four thin grey, partially interrupted cross bars. Dorsal margin of pectoral-fin base with a short, grey stripe.

Preserved. Straw-yellow, vague remnants of the patterns of spots, stripes and bars discernible in some specimen.

Etymology. From the Latin ‘insularis’, meaning ‘of an island’, in reference to the distribution of the species, which is apparently confined to the Cocos (Keeling) Islands.

Distribution. Currently known only from Cocos (Keeling) Islands in the eastern Indian Ocean ( Fig. 18 ), where it appears to be common.

Comparisons. Among the species with a vertically sided interorbital trench, the new species is the only one which lacks a completely scaled predorsal midline, usually has 10 rays in the second dorsal fin (vs. usually 8), and has an oblique yellow stripe across the cheek below the eye. Several other species of Trimma have a somewhat similar colour pattern, especially on the body. The new species differs from all of these in the presence of a continuous diagonal yellow to orange stripe from the tip of the upper jaw to the upper margin of the opercle, and in usually lacking scales in the predorsal midline (0–3 vs 4 or more). It differs further from T. annosum and T. fucatum Winterbottom & Southcott 2007 —in both of which the cheek is uniformly pigmented—in lacking opercular scales, usually having more dorsal- and anal-fin rays (9–10 vs. 7–9), and in having branched rays in the pectoral fin (vs. all unbranched). Trimma okinawae and T. readerae sp. nov. have an unbranched (vs. branched) fifth pelvic-fin ray and a light coloured vertical bar or two vertically aligned light spots on the cheek immediately below the eye. Trimma maiandros also usually lacks scales in the predorsal midline (although a few may be present). However, it lacks elongated spines in the first dorsal fin, has continuous yellow basal stripes in the dorsal fins (rather than spots), and has more distinct and wider (almost eye width) bars on the body that usually extend ventrally to the midline (vs. half pupil diameter in width and not reaching midline). Trimma necopinum has a somewhat similar orange or red bar across the cheek, but it extends only halfway to the jaws, and the species lacks a deep interorbital trench, has a fifth pelvic ray with two dichotomous branches (vs. 0–1), the anterior extent of the body scales does not extend anteriorly beyond the posterodorsal region of the opercle (vs. to posterior border of eye), lacks scales on the dorsal margin of the opercle (vs. present), and has more, and more regular, orange to red spots on the body.

No specimens of T. insularum were available for DNA analysis.

Discussion. The new species is unusual in its apparently extremely limited distribution ( Cocos (Keeling) Islands only, Fig. 18 ), where, judging by the frequency of collection and the number of specimens per lot, it is abundant.

Figures

FIGURE 17. Trimma insularum, 18 mm SL, Cocos (Keeling) Ids. Photo by G. R. Allen.

FIGURE 18. Map of the distributions of Trimma insularum (solid squares with white centers), T. kitrinum (solid inverted triangles) and T. lantana (solid circles with white star).