Akheilos, White & Weigmann, 2019

White, William T. & Weigmann, Simon, 2019, A new genus and species of catshark (Carcharhiniformes: Scyliorhinidae) from eastern Indonesia, Zootaxa 4691 (5), pp. 444-460 : 445-446

Genus Akheilos n. gen. White, Fahmi & Weigmann

Definition. Scyliorhinid with firm body (not soft and flabby); trunk relatively short, 40.4% TL; tail moderately long (60% TL) and moderately slender (width at pelvic-fin insertions 4.8% TL), tapering weakly to caudal fin; caudal peduncle moderately long, dorsal-caudal space 1.1 times second dorsal-fin base, anal-caudal space 1.1 times analfin base. Head short, about 17% TL; eyes lenticular, with broad subocular ridges; anterior nasal flaps not reaching mouth, without barbels; posterior nasal flaps present; labial furrows well developed on both jaws, uppers long but not reaching symphysis and about half nostril width; gill slits lateral on head.

Posterior teeth grading into anterolaterals in both jaws, not obviously dimorphic; cusplets not shifted posteriorly. Tooth row count ~60/~53. Jaws with relatively thick and dense cartilage; ventro-labial cartilage large; Meckel’s cartilage indented on bottom edge.

Pelvic fins slightly smaller than anal fin; inner margins not fused over claspers in adult males. Claspers with well-developed envelope, pseudosiphon, pseudopera, cover rhipidion, rhipidion and exorhipidion; cover rhipidion small, without an anterior fold or tab; pseudosiphon small and with a short slit-like aperture; rhipidion short and not extending well posterior on clasper glans.

Dorsal fins subequal in size; second dorsal fin slightly smaller in size to anal fin, with base 0.6 times anal-fin base and 1.3 times anal-fin height, slightly larger than pelvic fins, origin just anterior to anal-fin insertion. Caudal fin without crests of enlarged denticles on the dorsal and/or ventral margins.

Cranium with tips of rostral cartilage fused into a rostral node. Anterior fontanelle broadly triangular, slightly wider than long. Postorbital processes low and broadly rounded, merging posteriorly with sphenopterotic ridges. Prominent supraorbital crests present. Occiput with low occipital condyles, not exserted posteriorly. Lower fourth extrabranchials present in branchial skeleton.

Pale brownish with dark brownish spots and ocelli.

Total vertebral count ~137, precaudal count 96.

Type species. Akheilos suwartanai n. sp. White, Fahmi & Weigmann

Etymology. Name comes from the Greek mythological sea daemon Akheilos who was a handsome boy transformed into a shark by the goddess Aphrodite as punishment for his boasting that he was more beautiful than her.

Remarks. The genus Akheilos belongs to the family Scyliorhinidae based on the presence of supraorbital crests on the chondrocranium. Within the Scyliorhinidae , Akheilos differs from the genera in the subfamily Scyliorhininae ( Cephaloscyllium , Poroderma and Scyliorhinus ) based on a combination of the following characters: dorsal fins subequal in size and height (vs. first much larger than second), second dorsal fin only slightly smaller in size to anal fin (vs. much smaller than anal fin), large ventro-labial cartilage on jaws (vs. ventro-labial cartilage small), pseudosiphon present on claspers (vs. absent), tips of rostral cartilage of cranium fused into a rostral node (vs. rostral cartilage tapering to abrupt free ends, not forming a rostral node), occiput of cranium with low occipital condyles, not exserted posteriorly (vs. high, posteriorly exserted occipital condyles), upper and lower labial furrows well developed and moderately long (vs. absent, confined to mouth corners or if moderately long on lower jaw only), and fourth extrabranchials present on branchial skeleton.

The genus Akheilos differs from the genera in the subfamily Atelomycterinae ( Atelomycterus and Aulohalaelurus ) in the following combination of characters: subocular ridges below eye broad (vs. narrow), posterior nasal flaps present (vs. absent), labial furrows moderately long with uppers not extending to symphysis and shorter than half of nostril width (vs. very long with uppers extending forward of symphysis and greater than nostril width), posterior teeth not well differentiated from anterior teeth in both jaws (vs. well differentiated), clasper pseudosiphon short (vs. very long), clasper cover rhipidion small and without an anterior tab or fold (vs. enlarged with a free, envelope-like anterior tab or fold), anterior fontanelle on cranium broad and semicircular (vs. narrow and longitudinally oval), intestinal valves with 8 (vs. 13–16) turns, and total vertebral centra ~137 (vs. 147–183).

The genus Akheilos shares many similar features to the genus Schroederichthys and we consider it to belong to the subfamily Schroederichthyinae. The addition of the new genus into this subfamily extends the distributional range of Schroederichthyinae from the Americas to eastern Indonesia. Akheilos differs from Schroederichthys in having more intestinal valve turns (8 vs. 6), clasper groove not fused dorsally between apopyle and hypopyle (vs. clasper groove fused), jaw with heavy cartilage density (vs. much lower density), lower anterior edge of Meckel’s cartilage with an indentation between symphysis and rear plate (vs. even from symphysis to rear plate), rear plate of Meckel’s cartilage narrow (vs. wide), anterior palatoquadrate sections not forming a cordiform shape at symphysis (vs. forming a distinct cordiform shape at symphysis), posterior ends of palatoquadrate tapered and somewhat pointed at articular section (vs. not tapered), a short gap present between posterior tooth files of upper jaw and articular portion (vs. a large gap), a distinct ridge in upper jaw above articular knob (vs. area above articular knob flat), central cusps of anterior teeth short and poorly developed (vs. long and well developed), teeth of adult males not distinctly dimorphic with lateral cusps well developed (vs. distinctly dimorphic with lateral cusps not well developed in adult males), teeth smaller, more numerous and condensed in placement (vs. teeth larger, fewer and more widely spaced), roots of upper teeth only mildly concave (vs. deeply concave), posterior tooth rows of lower jaw arranged in diagonal file pattern (vs. not arranged in diagonal file pattern), orbital process of jaw small and knob-like (vs. wide and expanded), ventral caudal lobe produced and distinct (vs. barely evident), anal fin slightly larger in area than second dorsal fin (vs. smaller than second dorsal fin), colour pattern (broken ocellus-like marking on postpectoral sides and below dorsal fins vs. no such ocellus-like marking on sides), and in the following morphometrics (see Table 1 ): a shorter anal-caudal space (7.9 vs. 11.4–22.1% TL) and pelvic-caudal space (29.8 vs. 35.6–43.9% TL), slightly longer preoral length (5.1 vs. 2.9–4.7% TL), a longer anal-fin posterior margin (8.1 vs. 4.8–7.0% TL), larger nostrils (nostril width 2.9 vs. 1.6–2.6% TL), and a longer pre-first dorsal length (46.0 vs. 34.7–43.9% TL).