Trimma berumeni sp. nov.

Figs 1, 2 Mikey’s golden pygmygoby

Type locality.

Saudi Arabia, Red Sea: Farasan Banks, 18.5041°N, 40.6606°E.

Type material.

Holotype • ROM 116871, 13.6 mm SL male, Red Sea, Saudi Arabia, Farasan Banks, 18.5041°N, 40.6606°E, inside cave of exposed reef wall, 27 m depth, collected with clove oil and hand net, V. N. Peinemann, 5 June 2024.

Paratypes • ROM 116872, n = 2, 13.3 mm SL male, Red Sea, Saudi Arabia, Farasan Banks, 18.5041°N, 40.6606°E, inside cave of exposed reef wall, 27 m and 15 m depth respectively, collected with holotype • ROM 116873, 13.8 mm SL male, Red Sea, Saudi Arabia, Farasan Banks, 18.8581°N, 40.3788°E, inside cave of exposed reef wall, 15 m depth, V. N. Peinemann, 6 June 2024 • ROM 116874, n = 3, 10.7 mm SL female, 10.9 mm SL male, and 10.7 mm SL male, Red Sea, Saudi Arabia, Farasan Banks, 19.8375°N, 39.9297°E, inside cave of exposed reef wall, 30 m depth, V. N. Peinemann, 19 May 2022.

Diagnosis.

A species of Trimma distinguished by the following combination of characters: predorsal midline with 7–8 scales; fifth pelvic-fin ray unbranched and 40–42 % length of fourth ray; cheek and opercle scaleless; all pectoral-fin rays unbranched; body bright yellow throughout and without bars in life; dorsal fin VI + I, 7; no elongate spines in dorsal fin; bony interorbital width 81–84 % of pupil diameter; iris golden-yellow with melanophores except for golden ring around pupil and inverted golden triangle extending from ventral margin of pupil; fins translucent with yellow-green longitudinal band in central third of dorsal fins; a thin black midlateral line from above pectoral-fin base to caudal-fin base, visible in life and in preservative.

Description.

Based on holotype and 6 paratypes 10.7–13.8 mm SL. Dorsal fin VI + I, 7, second spine longest but not elongate extending to base of second dorsal-fin spine when adpressed; all rays of second dorsal fin branched; second dorsal fin not elongate, reaching posteriorly 23–26 – 30 (27 %, 7) of caudal peduncle length; anal fin I, 8, all rays branched; anal fin not elongate, reaching posteriorly 23–30 (27 %, 7) of caudal peduncle length; pectoral-fin rays 14–15, all unbranched; pectoral-fin reaching posteriorly to vertical above urogenital papilla; pelvic fin I, 5, fifth ray unbranched and 40–42 (41 %, 7) length of fourth ray, which reaches posteriorly to between base of first and third anal-fin ray, pelvic rays 1 to 4 with one branching point each; basal membrane approximately 9–10 % of fourth pelvic-fin ray; no fraenum; caudal fin with 2 dorsal and 2–3 ventral segmented unbranched rays, and 6 dorsal and 5 ventral segmented branched rays; caudal fin with four vertically aligned papillae at base and three rows of 9–10 papillae each extending from the vertically aligned papillae to posterior margin of caudal fin (Fig. 2 D); male urogenital papilla elongated and narrow (Fig. 2 E; female urogenital papilla short and bulbous (Fig. 2 F).

Lateral scales 24; anterior transverse scales 7–8, posterior transverse scales 7–8; cheek and opercle scaleless; 7–8 scales on predorsal midline; body scales ctenoid; circumpeduncular scales 12; scale rows in ventral midline between base of last anal-fin ray and first procurrent caudal-fin ray 7–8.

Gill opening extending anteroventrally to between middle and posterior third of pupil (Fig. 2 C); anterior naris tubular reaching anteriorly across upper lip to posterior margin of lower lip; posterior naris oval and pore-like with raised rim, separated from bony front of orbit by 1.6–2 times its diameter (Fig. 2 B); bony interorbital width 81–84 % of pupil diameter (82 %, 7); no dermal ridge on midline of nape extending anteriorly from origin of first dorsal fin.

Caudal peduncle depth as percentage of caudal peduncle length 30–41 (37.2 %, 7); head length as percentage of SL 27–29 – 31 (29.3 %, 7); horizontal eye diameter 40–45 (43.1 %, 7); snout length 16–20 (18.9 %, 7); and upper-jaw length 32–33 (32.6 %, 7) as percentage of head length

Number of papillae in each row (Fig. 2 A): a = 6 (4); b = 1–2 (5); c = 5 (5); d = 3–4 (5); d’ = 3–4 (5); p = 6 (5); e-anterior = 7–9 (5); e-posterior = 7–9 (5); i-anterior = 6–7 (5); i-posterior = 7 (5); cs ” = 3 (5); ot = 7–8 (4); oi = 3–4 (4); u = 4 (3); cp = 1 (5); n = 1 (5); f = 2–3 (5).

Color pattern, live (Fig. 1). Body bright yellow throughout. Head primarily yellow with orange coloration around the jaws, snout, interorbital region and below the ventral margin of the eye. Individuals can activate five translucent whitish bars along dorsal margin of body, from above the pectoral fin base to the caudal peduncle, sometimes visible in situ. Head and body with numerous small melanophores scattered throughout, running along scale pockets in the dorsal third of body, and scattered without patterns below the midlateral line. Specimens smaller than 11 mm SL with few melanophores on ventral half of body. A thin black midlateral line running along body from above pectoral-fin base to caudal-fin base. Iris golden-yellow, peppered with melanophores, except in a golden ring surrounding the pupil and an inverted golden triangle extending from ventral margin of the pupil. Dorsal fins translucent with dense red, white, and black chromatophores along basal third, a yellow-green longitudinal band running along central third, and sparse red, white, and black chromatophores along distal third. Anal fin mostly translucent with red, white, and black chromatophores, without yellow-green pigmentation. Dorsal and ventral fifths of caudal fin translucent with scattered red and white chromatophores, central section of caudal fin yellow to yellow-green. Pectoral fins and pelvic fins hyaline.

Color pattern, preserved (Fig. 2 G). Head and body primarily light yellow in large and recently preserved specimens, slowly fading to white in small specimens older than a year. Melanophores remain scattered throughout. A thin black midlateral line just under scales, extending from above pectoral-fin base to caudal-fin base. Iris densely packed with melanophores, appearing mostly black. Dorsal and anal fins hyaline with melanophores scattered in the posterior third of each fin, growing denser towards the posterior margin of the fin. Pectoral, pelvic, and caudal fins hyaline.

Etymology.

Named in honor of Michael L. Berumen in recognition of his substantial contributions to our understanding of the ecology and biodiversity of Red Sea coral reefs. Mikey’s golden pygmygoby is suggested as the common name.

Distribution and habitat.

Trimma berumeni sp. nov. inhabits caves of exposed offshore reefs, where it moves along the surface of cave roofs and walls in small groups of three to ten individuals (occasionally it is also solitary). It is typically found deep within caves, rarely seen within the first 80 cm of a cave entrance. The habitat is similar to that of its sister species, Trimma winchi, in the Seychelles (Ryan Daly pers. comm.).

Specimens were collected at depths between 15 and 30 m. While only two specimens were observed shallower than 20 m, the species is relatively common in caves at 30 m. Our collections and surveys were limited to 30 m, but it is likely that the species extends to greater depths. We observed this species exclusively on reefs with steep walls that extend well into the mesophotic.

The species is present throughout much of the Farasan Banks in the southeastern Red Sea (Fig. 3). Despite extensive collections in similar habitats along the Saudi Arabian coastline north of the Farasan Banks, from Jeddah to Tiran, we have not observed this species anywhere but the Farasan Banks. It is possible that the species is endemic to the southern half of the Red Sea.

Comparisons

In the key to the genus (Winterbottom 2019), T. berumeni keys out to couplet 71 but does not match either of the two species in the couplet. Trimma berumeni differs from both in having 7 dorsal fin rays (vs 9 in Trimma imaii Suzuki & Senou, 2009 and 8 in Trimma matsunoi Suzuki Sakaue & Senou, 2012). It additionally differs from T. imaii in having a bony interorbital width wider than 80 % of pupil width (vs 40 % in T. imaii) and from T. matsunoi in having 7–8 predorsal midline scales (vs 6 in T. matsunoi). The general body, fin, and eye color is also clearly distinct in each species.

In overall morphology, the T. berumeni is most similar to T. winchi, which is currently known from the Seychelles and the Chagos Archipelago (Fig. 4 A). They share a uniform yellow body color, have a similar habitat, and a geographically close but non-overlapping distribution. The COI sequences of T. berumeni and T. winchi differ by a K 2 P distance of 6.4 % (see Suppl. material 3 for K 2 P distances of Red Sea Trimma and sister taxa in Fig. 5 B). Several traits can be used to separate the two species. These are summarized in Table 1. Notably, the two Chagos (type locality) male specimens of T. winchi have an elongate dorsal spine, which is absent in Ryan Daly’s photographs of T. winchi from the Seychelles. It has not been evaluated whether this represents a distinct species or intraspecific variation. In Table 1 we follow the original description in listing dorsal-spine elongation for T. winchi, but the variation warrants further investigation.

Within the Red Sea, T. fishelsoni bears some similarity to T. berumeni. Both species have a primarily yellow body color, a yellow longitudinal band along the dorsal fins, and a primarily yellow caudal fin. Both species also have an overlapping distribution in the central to southern Red Sea and are associated with caves. Trimma berumeni can be distinguished from T. fishelsoni by having no elongate dorsal spines (vs second spine elongate and filamentous in T. fishelsoni), 7–8 predorsal midline scales (vs 9–14 in T. fishelsoni), scaleless cheek and operculum (vs scaled in T. fishelsoni), a basal membrane connecting the fifth pelvic fin rays (vs absent in T. fishelsoni). The live color of T. berumeni differs by the body being bright yellow throughout (vs yellow with a white to purple stripe above midlateral line in T. fishelsoni), head yellow throughout (vs primarily pale to pink in lower jaw and ventrally of eye in T. fishelsoni), no longitudinal yellow band on anal fin (vs usually present in T. fishelsoni), no blotches at caudal fin base (vs two large vertically aligned yellow-orange blotches at caudal fin base in T. fishelsoni), and no lines across iris (vs oblique blue line with orange-red margins across upper edge of pupil in T. fishelsoni).

Bogorodsky et al. (2016) extended the known range of T. fishelsoni from the northern Red Sea to the Farasan Banks, while noting some morphological differences between the populations. The southern population has no branching pectoral fin rays while northern ones have some. Southern populations lack the four saddle-like dorsal blotches described for Gulf of Aqaba specimens (more apparent in preservative) by Goren (1984). Gulf of Aqaba specimens (Fig. 4 B) also appear to have a yellow patch at the posterior margin of the jaw that is absent or less distinctive in southern populations. We have collected specimens from the central Red Sea with a mostly pale dorsal body color and 5 or 7 dusky yellow dorsal blotches (either a single large or two smaller blotches are present under each dorsal fin) that were apparent in live, freshly dead, and preserved individuals (Fig. 4 C). These individuals have no branching pectoral fin rays and a much fainter yellow color on the anal fin. While further analyses and additional specimens are needed to determine the nature of this variation between T. fishelsoni populations, the differences to T. berumeni discussed above are consistent across populations.