Trimma milta Winterbottom, 2002

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 : 55-58

Trimma milta Winterbottom, 2002

Red-earth Pygmygoby (Moorea Pygmygoby) Figs. 30–31 , Pl. 2 E

Trimma milta Winterbottom, 2002:46 (Moorea, Society Ids, widespread in western Pacific, 4 figs.); Kimura & Matsuura, 2003:192 (Bitung, N. Sulawesi); Randall, 2005:553 (photo from Hawaii); Bacchet et al., 2006:456; Suzuki et al., 2007a:77 (first record from Japan); Allen & Erdmann, 2012:942 ( Taiwan to Solomon Ids, and Australia); Motomura et al., 2013: 338 ( Japan).

Trimma winchi (non Winterbottom,1984): Hayashi & Shiratori, 2003:39 (identity uncertain). Trimma sp. A: Myers, 1999:pl.163.

Material. In addition to the type material from the Society Islands, we have examined specimens from the following localities:

Australian Material. Great Barrier Reef: Escape Reef: AMS I.22580-021, 6(17–20), 37 m; AMS I.22587- 0 21, 8(16–21), 40 m; AMS I.22613-043, (17–20), 27 m; AMS I.22627-016, 6(19–23), 56–60 m; AMS I.22629- 0 0 8, 13(15–21), 56–60 m; AMS I.22637-047, (18), 3– 15 m.; USNM. Herald Cays: WAM P. 28537.029, (18), 15– 25 m. Osprey Reef: AMS I.25107-051 3(17–21), 10– 25 m. Raine Id: AMS. Yonge Reef: AMS I.19454-062, 20(10–22), 1– 18 m. Western Australia: Ashmore Reef: WAM P. 29047.036, 2(19–19), 20– 25 m. Rowley Shoals: WAM P. 28024.022, 7(14–18), 35–40 m; WAM P. 28026.026, (22), 33–40 m; WAM P. 28034.016, (17), 33– 40 m.

Other Material. Fiji: Viti Levu: AMS, ROM. Hawaii: BPBM, ROM. Indonesia: Lucipara Ids: ROM. Moluccas: USNM. Raja Ampat Ids: ROM. Marshalls: Enewetok: BPBM. Kwajalein: BPBM. Micronesia: Ant Atoll: USNM. Ponape: USNM. Ulithi Atoll: BPBM. Palau: AMS, BPBM, ROM. Papua New Guinea: Hermit Ids: USNM. Manus Id: WAM. Rabaul: ROM. Philippines: Balicasag Id: USNM. Cocoro Id: USNM. Siquijor Id: ROM, USNM. Solomons: Florida Id: AMS. Taiwan: BPBM.

Diagnosis. A species of Trimma with a concave bony interorbital less than half the pupil-diameter in width, the scale pockets strongly outlined with chromatophores, 6–8 scales in the midline of the predorsal region and 2–3 cycloid scales on the upper margin of the opercle, fifth pelvic-fin ray unbranched and about half the length of the fourth, no trough or groove posterodorsal to the eye, epaxial musculature reaching anteromedially to a point in line with the posterior margins of the pupils in adults, and no greatly elongated spines in the first dorsal fin (longest spine reaching to, or slightly beyond, origin of second dorsal fin when fin is adpressed).

Description. The description is based primarily on the holotype, and 19 paratypes (9 male, 10 female) from ROM 59751, and taken from Winterbottom (2002). Dorsal fins VI + I 9, second and third spines longest but not elongated, reaching about to origin of second dorsal fin when adpressed, first ray of second dorsal usually branched; anal fin I 8, first ray usually unbranched; pectoral fin 17–18 (mean = 17.3), at least upper 3 and lower 4 unbranched, although all rays may be unbranched in small specimens (about 11 mm SL); pelvic fin I 5, first four rays with single sequential branching pattern, fifth ray unbranched, and about half length of longer of two branches of fourth ray, no fraenum, basal membrane restricted to distal one-tenth of inter-pelvic gap. Lateral scales 22 (1), 23, 24 (mean = 23.1); predorsal scales 6, 7, 8 (mean = 7.1); transverse scales 6.5; nape, opercle, pectoral-fin base, breast and midline of belly with cycloid scales, ctenoid scales posterior to line between upper opercular margin and origin of first dorsal fin; opercle with a single horizontal row of 2–3 scales across upper margin; pectoral-fin base margined by four scales. Teeth of outer row of upper jaw, and outer and inner rows of lower jaw consist of enlarged, curved, evenly spaced canines, with several irregular rows of small conical teeth behind outer rows. Tongue broadly rounded, about half pupil-diameter in width. Gill opening to below midpoint of pupil; outer gill rakers of first gill arch 3–4 + 12–15 (holotype 14, mean = 13.7). Anterior nares a short tube, posterior nares porelike with raised rim, nasal sac slightly raised, with nasal apparatus confined to anterior half of snout. A shallow interorbital trough; none posterodorsal to eye; bony interorbital width equal to less than half-pupil diameter; epaxialis musculature reaching anteriorly to above posterior margin of pupil. Abdominal/caudal vertebral transition Type B.

Colour pattern. Freshly collected. Based on 35 mm colour slides of 4 males, 19.2–22.1 mm SL and 4 females, 14.7–19.2 mm SL). Overall colour brownish red with centres of scales lighter orange-red, mingled with melanophores, especially on head and anterior body. First dorsal fin with row of yellow spots just distal to base of fin, one spot on each spine, or spots tending to form or forming a yellow stripe, rest of fin membrane sprinkled with melanophores. Second dorsal fin with similar row of yellow spots on each fin ray (not forming a stripe); some individuals with additional but more diffuse row of yellow spots centred on fin rays in region of first branch; rest of fin sprinkled with melanophores. Caudal-fin membrane with melanophores, and with 0–3 vertical rows of light yellow spots. Anal fin with melanophores, sometimes diffuse light yellow band or few yellow spots just distal to fin base. Pectoral and pelvic fins hyaline, iris red with dark patches. Two very diffuse lighter bars under eye, third along vertical limb of preopercle. One specimen (female, 19.2 mm SL) more yellowish than others, with three light cheek bars better defined (see also Fig. 30 ). Raja Ampat female (17.6 mm SL) with translucent pale pink body and margins of scales (especially anteriorly) outlined with magenta, lighter bars on cheek and along vertical limb of preopercle are yellow ( Fig. 30 ). This is similar to live specimen from Wetar, Indonesia (Pl. 2 D), which differs in having scale margins brown and in lacking yellow bars below the eye.

Preserved. Scale margins, pockets, and head with dark brown chromatophores and melanophores, centres of scales and yellow spots/stripe pale. Degree of chromatophore/melanophore intensity decreases posteriorly along body, where some specimens are pale straw-coloured. Two to four narrow transverse bands of melanophores across dorsal rim of orbit usually present.

Etymology. From the Greek 'miltos' for red earth, in allusion to the predominant ground colour of the species and the colour of the topsoil of the islands in the type locality.

Distribution. Recorded from numerous Pacific localities, from Rowley Shoals north to southern Taiwan, Hawaii, Society Islands (where it is numerically the dominate species of the genus), west to northern Australia and Sulawesi ( Fig. 31 ).

Comparisons. This species belongs to a complex of 10 species possessing a scaled predorsal region and scale pockets on the body outlined with chromatophores and/or melanophores. Three species in the complex have been named, T. anthrenum Winterbottom, 2006 , T. emeryi and T. preclarum (see Winterbottom, 2006 for descriptions and comparisons). Trimma milta is the only species in the complex which possesses opercular scales and an unbranched fifth pelvic fin-ray (occasional specimens of T. preclarum may have an unbranched fifth pelvic ray in a few localities). It can be further distinguished from an undescribed species which has opercular scales and an unbranched fifth pelvic-fin ray by the lack of a elongated second spine of the first dorsal fin and in having fewer lower gill rakers on the outer surface of the first gill arch (13–14 vs. 16).

Analysis of the CO1 genome of 21 specimens resulted in the identification of four haplogroups, three of which are currently restricted to a single area ( Winterbottom et al. 2014). The first three are Moorea, Society Islands (the type locality, n = 4), Fiji (n = 2), and Palau (n = 10). The fourth group contains specimens from Raja Ampat, Indonesia (n = 2), Palau (n = 1) and Flores, Indonesia (n = 1). Further studies of both morphology and genetics are clearly needed to resolve, if possible, the variation described above. For the present, in view of the absence of positive evidence and the lack of tissue samples, we retain the Australian population in T. milta . The species has the Australian standard name of Moorea Pygmygoby.

Discussion. Specimens from the Great Barrier Reef have a slightly higher average pectoral-fin ray counts (mean = 17.8, n = 9), lateral-scale counts (mean = 23.9, n = 8) and outer gill rakers (mean = 3.8 + 14.4, n = 8), whereas those from Western Australia were more similar in these values to the type specimens but differed in that two (of seven) specimens had eight (instead of nine) rays in the second dorsal fin. The fresh colouration of Australian specimens has yet to be recorded. Several freshly collected photographed specimens from Palau were yellow with a yellow stripe in each of the dorsal fins just above a basal dark stripe. In addition, specimens from Micronesia and the Hermit Islands do not seem to reach as large a size as those from elsewhere (maximum recorded SL was 18.2 mm out of 230 specimens vs. a maximum of nearly 24 mm SL elsewhere). Finally, none of the Micronesian/New Guinea specimens examined had the short transverse bars across the top of the eye that are present in most (but not all) specimens from other areas. The species is found in depths of 3– 60 m. In Australia it is known only from clear water outer reefs on the Great Barrier Reef and Timor Sea. It has been referred to informally as Trimma DFH sp. 7 or Trimma RW sp. 34.

Figures

FIGURE 30. Trimma milta, 17.6 mm SL female, ROM 85066, Quoy Id., Raja Ampat Ids. Photo by R. Winterbottom.

FIGURE 31. Map of the distribution of Trimma milta (solid inverted triangles) and T. nasa (solid circles with white star).