Gymnothorax hepaticus (Rüppell 1830) —Yellow-jaw Moray

(Figures 17–20)

Muraena hepatica Rüppell 1830: 120 (Red Sea). Holotype (unique), SMF 3554.

Gymnothorax hepatica: Bamber 1915: 478 (part?).

Gymnothorax hepaticus: Clark et al. 1968: 21 (part?); Goren & Dor 1994: 7 (part?); Randall & Golani 1995: 858 (part?); Golani & Bogorodsky 2010: 10 (part?); Golani & Fricke 2018: 21 (part?).

Lycodontis hepaticus: Dor 1984: 28 (part?).

Gymnothorax monochrous (non Bleeker): Debelius 1998: 14; Khalaf 2004: 36 (part?).

Red Sea material. Red Sea: SMF 3554 (1, 535, holotype), no further data; SMF 35879 (1, 260; out of SMF 185). Saudi Arabia: SMF 35811 [KAU14-302] (1, 490), Red Sea, Saudi Arabia, off Jizan, sand bottom, 16°54’ N 42°28’ E, 15–17 m, 01 Nov. 2014, T.J. Alpermann, S.V. Bogorodsky, A.O. Mal & M. Gabr ; SMF 35876 [KAU17-139] (1, 240), Red Sea, Saudi Arabia, Farasan Archipelago, Dumsuk Island, reef slope with mix of rocks and corals, 16°33’N 42°04’E, 12–14 m, 07 Feb. 2017, T.J. Alpermann & S.V. Bogorodsky ; KAUMM 452 [KAU17-156] (1, 468), the same locality; USNM 444253 [KAU17-155] (1, 345), same locality; SMF 35879 [ex SMF185] (1 of originally 3 in SMF 185, 260), Al Muwaylih. Eritrea: USNM 312567 (2, 175–178), Massawa; USNM 312568 (4, 114–195), Dahlak Archipelago, Delemmi .

Diagnosis. Medium-sized moray, moderate in length and depth, tail relatively slender, head behind eye distinctly elevated. Preanal length 1.9–2.1 in TL. Third intermaxillary tooth somewhat distant from vertical at anterior margin of eye. Upper head and body plain brown without markings; lower jaw and ventral part of branchial area pale yellow in life; margin of dorsal and anal fins pale grey to yellowish at tip of tail. Vertebrae 4–6 / 58–61 / 128–132.

Description. In TL: preanal length 1.9–2.1, predorsal length 9.0–11, head length 7.1–7.8, body depth at gill opening 13–23, depth at anus 15–23. In head length: snout length 5.0–5.9, eye diameter 9.0–11, upper-jaw length 2.5–3.0. Pores: LL 2, SO 3, IO 4, POM 6. Vertebrae: predorsal 4–6, preanal 58–61, total 128–132.

Body moderately elongate, anus near midlength, tail relatively slender; dorsal-fin-origin before gill opening, anal fin beginning immediately behind anus. Head with a distinctly raised profile behind eyes; jaws and snout moderately slender and slightly arched, a slight gap visible when mouth closed, upper and lower jaws nearly equal in length. Eye moderate, over middle of upper jaw. Gill opening small, slightly elongate, on side of head slightly below lateral midline. Anterior nostril tubular, relatively short, not reaching edge of lip when depressed. Posterior nostril oval, with a slightly raised rim, above eye, its anterior margin about level with anterior margin of eye. Third infraorbital pore at or slightly ahead of anterior margin of eye.

Teeth smooth, slender and pointed or blade-like. Intermaxillary teeth in one peripheral series of 4–6 on each side, increasing in size from anterior to posterior, and a median series of three sharp, depressible teeth, increasing in size from anterior to posterior. Third intermaxillary tooth somewhat distant from vertical through anterior margin of eye, ratio between distance from third intermaxillary tooth to tip of snout and distance from same tooth to anterior margin of eye 1.8–3.0. Maxillary teeth uniserial or biserial; inner row with 0–3 larger teeth anteriorly; outer teeth smaller, about 9–16. Dentary teeth uniserial, the largest in front, decreasing in size posteriorly; 12–21 full-sized teeth with 1–3 much smaller teeth anteriorly between large teeth. Vomerine teeth inconspicuous, uniserial or slightly irregular.

Color: brown without markings on body, lower jaw and ventral part of branchial area pale yellow in life, throat grooves slightly darker. Head pores without dark margin. Fins dark with an inconspicuous pale edge posteriorly.

Size. The specimens range in size from 114 to 535 mm TL. They are all immature.

Distribution and habitat. The known specimens were all collected from the southern Red Sea. It seems less common than Gymnothorax cinerascens, but the two species have not been distinguished previously, and the actual abundance and distribution are still uncertain. Most specimens were collected in coral-reef areas with mix of rocks and corals from depths of 12–17 m; one specimen was trawled from soft substrata.

Remarks. As noted, this species has long been confused with Gymnothorax cinerascens, and both species have likely been reported as G. hepaticus . The original descriptions are brief and largely devoid of distinguishing characters. The two species are similar in general appearance but can be distinguished by several characters. The preanal length is slightly greater in G. hepaticus (1.9–2.1, mean 2.0 in TL) than in G. cinerascens (2.0–2.2, mean 2.1 in TL) (Fig. 20A); this is reflected in the number of preanal vertebrae, 58–61 vs. 55–57 respectively. Gymnothorax hepaticus is somewhat lighter in overall color, and the lower jaw and ventral part of the branchial area are yellowish in life, pale in preserved specimens. Gymnothorax cinerascens is usually uniformly dark brown, including all of the head and lower jaw; some specimens are light gray-brown with scattered small dark patches, but none have the yellow lower jaw. The head pores have dark rims in G. cinerascens, whereas in G. hepaticus they are unmarked. The median intermaxillary teeth are distinctly closer to the eye in G. cinerascens than in G. hepaticus . In G. cinerascens, the distance from the third median intermaxillary tooth to the anterior margin of the eye is contained 3.2–12.6 times in the distance from the same tooth to the tip of the snout, compared to 1.8–3.0 times in G. hepaticus (Fig. 20B). The vomerine teeth in G. cinerascens are more numerous and distinctly biserial in adults, whereas in G. hepaticus they are fewer and uniserial or at most slightly irregular. The third infraorbital pore is located behind the anterior margin of the eye in G. cinerascens, whereas in G. hepaticus it is under or slightly ahead of that point. There are also a couple of differences in shape between the two species. The dorsal profile of the head relatively straighter in G. cinerascens, only slightly elevated behind the eye. In G. hepaticus, there is a more distinct hump behind the eye, although this is more obvious in larger specimens. Gymnothorax hepaticus has a more slender tail than G. cinerascens, a character that becomes apparent when they are examined side by side.

The two species are genetically distinct, and this is what brought them to our attention. We had originally treated this as a new species, but a re-examination of the holotypes showed that they correspond to Rüppell’s two species. The four COI sequences from the Red Sea specimens collected during the present study showed no substantial variation and formed a clade that was closely affiliated with a specimen from New South Wales, Australia, identified as G. monochrous (Bleeker), another uniformly colored species. Among four other species that were grouped with G. hepaticus and G. monochrous in a larger clade that received moderately high support were Enchelycore schismatorhynchus and an unidentified species from South Africa ( Gymnothorax sp. 3) and two distinct lineages, both identified as G. reevesi (Richardson) by the respective sequence authors. It is unknown whether either G. cinerascens or G. hepaticus occurs outside the Red Sea. The plain brown Gymnothorax are confusing and need to be studied in more detail to sort them out.