Enneapterygius rhothion Fricke, 1997

Dewa, Yuna & Motomura, Hiroyuki, 2024, First records of two triplefins, Enneapterygius rhothion and Enneapterygius olivaceus (Actinopterygii: Blenniiformes: Tripterygiidae), from Australia and Vanuatu, Acta Ichthyologica et Piscatoria 54, pp. 261-268 : 261-268

Enneapterygius rhothion Fricke, 1997

English name: New Caledonian blackhead surf triplefin Figs 1 , 2 , 3 ; Table 1

Material examined.

AMS I. 5088 , male, 32.5 mm SL, Green Island , Queensland, Australia, 17°13′48″S, 145°58′11″E, 1901, C. Hedley leg.

Description.

Counts and measurements given in Table 1 . Body moderately elongate, slightly compressed anteriorly, progressively more compressed posteriorly (Fig. 1 A ). Dorsal profile of snout straight, steep. Mouth slightly oblique; posterior margin of maxilla extending beyond anterior margin of pupil; anterior tip of upper jaw slightly above level of lower margin of orbit (lateral view). Medial supratemporal canal with two branches (Fig. 2 A ). Anterior nostril a membranous tube, at mid-eye level, slightly closer to eye than to upper lip; nasal tentacle slender, unbranched, with pointed tip; posterior nostril opening circular, without membranous tube (Fig. 2 A ). Eye oriented dorsolaterally, with small, pointed tentacle, slightly longer than nasal tentacle, on posterodorsal margin. Interorbital space narrow, its width less than pupil diameter. Opercular margin slightly pointed, reaching below base of 3 rd spine of first dorsal fin.

Lateral line discontinuous, with anterior series of pored scales ending below base of 11 th spine of 2 nd dorsal fin; second scale of posterior series of notched scales below third scale from last pored scale, ending at caudal-fin base; body scales ctenoid; scales absent on head (including maxilla, interorbital space, preopercle, and opercle), pectoral-fin base, pre- and inter-pelvic-fin region, abdomen, pre-dorsal-fin region, and all fin membranes, except basal part of caudal fin.

First dorsal fin triangular, origin over and slightly forward of midpoint between pre-opercular and opercular margins; 1 st spine of first dorsal fin damaged, 2 nd spine longer than 3 rd spine. Origin of second dorsal fin just above 4 th pored lateral-line scale, 3 rd spine longest, spines thereafter becoming gradually shorter posteriorly, forming rounded margin. Third dorsal fin damaged, its origin just above 20 th scale row of longitudinal series. Anal-fin membranous margin deeply incised between rays; anal fin origin just below 7 th spine base of second dorsal fin, its posteriormost tip close to caudal-fin base. Pectoral fin damaged (posterior tip lost); upper and lowermost pectoral-fin base level with bases of 3 rd and 2 nd spines, respectively, of first dorsal fin. Pelvic fin origin vertically below base of 1 st spine of first dorsal fin. Caudal fin rounded, its length less than head length.

Nuptial male coloration

(in preservative). Based on Fig. 1 A . Body generally yellowish white; brownish pigmentation forming faint A- and X-shaped bars on lateral surface of body. Head, including snout, lips, cheek, and opercle, and pectoral-fin base brown with numerous melanophores. Pre-pelvic region brown (extending to just behind pelvic-fin base). Orbital tentacle pale brown. First and second dorsal fins dark brown. Third dorsal fin damaged, but brownish basally. Pectoral, pelvic, anal and caudal fins whitish.

Distribution.

Currently known from New Caledonia (Chesterfield Islands, Grande Terre, Ile des Pins, and Loyalty Islands), Vanuatu (Erromango Island), and Australia ( Fricke 1997, 2002; this study) (Fig. 3 ).

Remarks.

The morphometric and meristic characters of the single specimen collected from Australia (AMS I. 5088, male, 32.5 mm SL) agreed closely with the type series of E. rhothion re-examined in this study (Table 1 ), and much of the original description of the species provided by Fricke (1997). However, although Fricke (1997) described the species as having a short orbital tentacle of length 0.6 % – 0.9 % of SL, both the presently reported specimen and holotype of E. rhothion had relatively long orbital tentacles (1.6 % – 2.1 % of SL). In addition, the mandibular pore formula of the species should be revised, the examined specimens having 3–4 + 2 + 3–4 (total 8–10 pores) [vs. 4–5 + 2 + 4–5 (total 10–12) in the original description]. Individual mandibular pore counts were as follows: 4 + 2 + 4 (holotype and 3 paratypes); 3 + 2 + 3 (4 paratypes and non-type Australian specimen); 4 + 1 + 4 (single paratype). The coloration of the presently reported specimen was consistent with that of E. rhothion shown in Fricke (1997): head, including snout, lips, cheek, and opercle, and pectoral-fin base black; lateral surface of body with faint bars; first and second dorsal fins black; anal fin pale (without markings). Although the color pattern of the caudal fin (dorsally and ventrally with faint vertical dark streaks; Fricke 1997) is one of the diagnostic characters for the species, such pigmentation was lost in the presently reported specimen after long-term preservation (Fig. 1 A ).

Enneapterygius rhothion was originally described based on 129 specimens from New Caledonia and Vanuatu. Subsequently, Fricke (2002) reported the species from Ile des Pins as an additional record of the species from New Caledonia. In addition, Randall (2005) showed a fresh photograph of a female individual of E. rhothion in his field guide. The species is one of the common triplefins in New Caledonian waters ( Fricke 1997, 2002). In his taxonomic works on triplefins, Fricke (2001, 2002) provided identification keys to the tripterygiid species in New Caledonian waters. Following those keys, the presently reported Australian specimen (AMS I. 5088, male, 32.5 mm SL) was identified as Enneapterygius rufopileus (Waite, 1904) . However, the keys described the number of symphyseal mandibular pores and the coloration of the second dorsal fin of E. rhothion erroneously [symphyseal mandibular pore 1, and second dorsal fin pale (rarely spotted) in males, respectively] (see Fricke 2001, 2002). Although E. rhothion is similar to E. rufopileus in scale counts and overall appearance, the former differs in having the following characters: symphyseal mandibular pore single (vs. double in E. rufopileus ), head (including maxillary) and pectoral-fin base entirely black (posterior two-thirds of jaws white, pectoral-fin base with black blotch), body with 7 bands (5 bands); first and second dorsal fin black in nuptial males (translucent white); third dorsal fin with black pigmentation in both sexes (not pigmented in either sex); dorsal and ventral parts of caudal fin with vertical streaks in both sexes (caudal fin pale in both sexes) ( Fricke 1997; this study).

Enneapterygius rhothion has previously been recorded only from New Caledonia (Chesterfield Islands, Grande Terre, Ile des Pins, and Loyalty Islands) and Vanuatu (Erromango Island), and was considered endemic to those areas ( Fricke 1997, 2002). The presently reported specimen represents the first record of the species from Australia, and the new northernmost record.

Figures

Figure 1. Photographs of preserved specimen of Enneapterygius rhothion (A: AMS I. 5088, male, 32.5 mm SL, Australia; B: SMNS 18322, holotype, male, 28.9 mm SL, New Caledonia, Photo by M. Meguro).

Figure 2. Photographs of A: dorsal and B: ventral views of head of Enneapterygius rhothion (AMS I. 5088, male, 32.5 mm SL, Australia), showing cephalic sensory system.

Figure 3. Distributional map of Enneapterygius rhothion (red circles) and E. olivaceus (blue triangles). Closed and open symbols indicate localities determined during the presently reported study and previous records, respectively. Black arrows indicate type localities of the two species.