Gymnothorax hansi , Phillip C. Heemstra, 2004

Phillip C. Heemstra, 2004, Gymnothorax hansi, a new species of moray eel (Teleostei: Anguilliformes: Muraenidae) from the Comoro Islands, Western Indian Ocean., Zootaxa 515, pp. 1-7: 2-7

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Gymnothorax hansi

sp. nov.

Gymnothorax hansi  ZBK  sp. nov. (Figs. 1-3)

Type material: holotype, SAIAB 38673 (101 cm TL, male), Comoro Ids, Grand Comoro (Ngazidja), south coast off Itsounzou (11E52' S, 43E23' E), depth approximately 143 m ; baited fish trap; 23 October 1991; P.C. Heemstra, collectorGoogleMaps  ; paratype, SAIAB 74102 (101 cm TL, female) and USNM 376770 (77 cm TL), same data as holotypeGoogleMaps  .

Diagnosis. A moderately large moray (maximum length at least 101 cm) of the subfamily Muraeninae, genus Gymnothorax  ZBK  (as defined by Böhlke et al., 1989); head plus body distinctly longer than tail; dorsal fin origin at vertical midway between gill opening and rear edge of eye. Jaws closing completely when mouth is shut; teeth sharp, caniniform, slightly curved, uniserial on maxillae and dentaries; longest intermaxillary tooth equals 64% eye diameter; branchial pores 2. Anterior nostril tube reaches well in front of snout; posterior nostril irregular, set in a low fleshy mound, with opening directed dorso-posteriorly. Adults chestnut brown dorsally on head, body and most of tail; dorsal and anal fins brown anteriorly, blackish posteriorly with a bright white margin from dorsal fin origin round tail tip to origin of anal fin; anterior nostril tube, posterior nostril mound and iris yellow; adult male with head and ventro-lateral part of body of adult male golden brown and several, irregular, distinct, dusky or black spots scattered over most of the body, tail and dorsal fin; adult female with head paler below and a few faint dusky spots on body and tail; both sexes with pores on jaws set in white spots.

Description. (Counts and measurements are given in Table 1.) Moderately elongate, pre-anus distance 54-60% TL; head length 11-12% TL; dorsal and anal fins moderately high, dorsal fin higher than anal; dorsal-fin origin on head slightly before first branchial pore. Gill opening a mid-lateral, slightly oblique slit, the lateral edge crescentic. Branchial pores inconspicuous. Counts of lateralis head pores are given in Table 1. Supra-orbital pores 3, the anteriormost (ethmoid) pore is between the base of the nostril tube and the upper lip, second pore of the supra-orbital canal is anterior to the base of the nostril tube. The missing pores of the infra-orbital series of the juvenile paratype are the posteriormost pore on each side. The posteriormost pore of the mandibular series is below the rictus. Median intermaxillary teeth: Holotype with 1 large tooth below middle of eye; female with an irregular series of 6 teeth, 4 in front of eye and 2 at level of eye; juvenile with 1 tooth in front of eye and 3 at level of eye. Upper jaw (maxillae + peripheral teeth of intermaxillary) teeth: male holotype 13L, 10R; female paratype 16L, 14R; juvenile 9 on both sides. Lower jaw teeth: holotype 11L, 12R; female 18L, 15R; juvenile 10L, 13R. Vomer with 3 or 4 hidden, minuscule teeth. Ostensibly the jaw teeth appear smooth, but with the 40 x magnification of a dissecting microscope the proximal edges of the largest intermaxillary, maxillary and dentary teeth show minuscule crenulations. Vertebrae: 4 predorsal, 82-84 preanal, 183-185 total.

Comparison with other species. In their catalogue of the type specimens of Indo-Pacific morays, Böhlke and Smith (2002) recognize ~ 100 valid species of the genus Gymnothorax  ZBK  . The vertebral counts for G. hansi  ZBK  are significantly higher than the number of vertebrae for all other Indo-Pacific Gymnothorax  ZBK  species for which counts are available, except Gymnothorax prolatus Sasaki & Amaoka  ZBK  , 1991 from Taiwan, Gymnothorax polyspondylus Boehlke & Randall  ZBK  , 2000 from Hawaii and Gymnothorax albimarginatus Temminck & Schlegel  , 1846 which is known from the Indo-central Pacific. Compared with G. prolatus  ZBK  , G. hansi  ZBK  has a larger head (HL 8.4-8.6 in TL; versus HL 11 in TL in prolatus  ZBK  ), deeper body (D/GO 14 in TL; versus 29 in TL for prolatus  ZBK  ); one row of maxillary teeth (biserial in prolatus  ZBK  ); and prolatus  ZBK  has the body and fins uniformly dark brown. Compared with G. polyspondylus  ZBK  , G. hansi  ZBK  has fewer vertebrae (82-84 pre-anal and 183-185 total, versus 89 pre-anal and 233 total vertebrae in polyspondylus  ZBK  ), deeper body (D/GO 25 in TL for polyspondylus  ZBK  ) and polyspondylus  ZBK  also lacks dark spots on the body and a white margin on the dorsal and anal fins.

Gymnothorax hansi  ZBK  is most similar to G. albimarginatus  , a large Pacific species, with vertebral counts of predorsal 4-7, preanal 91-94, total 184-195 (based on 7 specimens, Böhlke & Randall, 2000). This species also has the anus behind mid body (head plus body longer than tail) and a similar colour pattern ( Böhlke & Randall, 2000: 227 “Overall coloration uniform medium brown, paler ventrally; head, snout and lower jaw pale; a round darker brown area on top of head behind eyes, and a less distinct dark area between and just before eyes, both areas noticeable on small specimens, faded and less distinct on large specimens but visible when viewed from above. Anterior nostril brown, posterior nostril in white spot; pores along both jaws in pale unpigmented spots. Fins dark or black basally, with white margin. Color notes on fresh specimens from Tahiti state: ‘Body brownish gray; tip of snout, lower jaw, and corner of mouth white; ground color of anterior half of head yellowish brown shading posteriorly to brownish gray; a large round dark brown spot on nape surrounded by a broad concentric ring a little paler than ground color; fins colored like body basally, shading to blackish distally, with white edge.’ Fresh specimens in alcohol appear medium brown, the fins dark with bright white edge, the spot on the nape appearing as a faded bulls eye”. In the photograph of the 698 mm G. albimarginatus  on Plate II of Böhlke & Randall’s paper, there is a faint line of tiny white dots along the front part of the lateral line and a white margin at the rear end of the mouth. The aquarium photograph on Plate VII shows a G. albimarginatus  with a pale brown head, rear nostrils and head pores in white spots, two dark rings on the nape, numerous faint white spots on the rear part of the head. G. hansi  ZBK  differs from albimarginatus  in having pale yellow nostrils, no ocellus on the nape, no white dots along the lateral line, and adult male with numerous irregular blackish spots and blotches on the body. The tooth counts given by Böhlke & Randall for G. albimarginatus  are similar to the counts for G. hansi  ZBK  , but it is difficult to compare them because the sexual differences in the tooth counts of G. albimarginatus  were not specified. Judging from the description of Böhlke & Randall, serrations on the teeth of G. albimarginatus  are more distinct than the weak crenellations of the G. hansi  ZBK  teeth.

In view of the differences in the numbers of preanal vertebrae (82-84 for 3 G. hansi  ZBK  , versus 91-94 for 7 G. albimarginatus  ), it seems reasonable to consider these two morays as distinct species. Small juveniles of G. hansi  ZBK  might be mistaken for Gymnothorax monochrous (Bleeker  , 1856) which is uniformly brown, but this species has the pale fin margin confined to the tail tip and fewer preanal vertebrae (56-61).

Remarks. The adult female paratype has a large ovary that extends almost the entire length of the abdominal cavity. The eggs are small, about 1.0 mm in diameter. The testis of the adult male holotype extends along the right side of the rear half of the abdominal cavity. The sausage-shaped swimbladder is well developed in both adults; it is located at the anterior end of the abdominal cavity; in the male it is 13 cm long by 22 mm in diameter. The teeth are more numerous in the adult female (30 total peripheral teeth in upper jaw and 33 teeth in lower jaw) than in the adult male (23 total peripheral teeth in both jaws). The same sexual dimorphism in number of teeth (females with more numerous teeth than males) was reported by Collette et al. (1991) for Gymnothorax parini  ZBK  and 4 other species Gymnothorax  ZBK  .

Distribution. Gymnothorax hansi  ZBK  is known only from deep water (~ 143 m) at Ngazidja (Grand Comoro Island). It was not observed during ~ 30 dives on the shallow fringing reef (5 to 50 m) at Ngazidja or Mayotte.

Etymology. This eel is named in honour of Prof Dr Hans Fricke, in recognition of his pioneering contributions to the study of fish behavior and the deep demersal fish communities of the Comoro Islands, Red Sea and Indo-Pacific region.