Milk-eye Catshark

description

Description of the specimens from the South China Sea. Proportional measurements are given in Table 1. Body slender, cylindrical before pelvic fins, gradually compressed laterally after pelvic fins. Caudal-peduncle height 49.2 – 67.6 % head height. Abdomen narrow, pectoral-fin free rear tip to pelvic-fin origin 54.3 – 86.2 % internarial width; pectoral-fin tip at or slightly extending after midpoint of space between pectoral and pelvic fins. Midpoint of the total length well behind cloaca. Head dorsoventrally flattened, its height 66.9 – 98.6 % greatest width of head. Snout rather long, tip rounded (Fig. 3). Pre-outer nostril length 42.2 – 49.4 % preorbital length, 83.6 – 101.3 % interorbital width. Nostril large, its length subequal to orbit length and internarial width, expanding obliquely inward towards mouth. Mouth considerably arched, its length 58.4 – 72.3 % width. Labial furrows well developed, length of lower labial furrows 44.5 – 77.3 % upper furrows; length of upper furrows 51.3 – 57.8 % mouth width. Orbit narrowly elliptical, with a poorly developed subocular fold. Spiracle small, bean-shaped, situated below a horizontal line through mid-eye. Five gill slits present; the

Occurrence of the milk-eye catshark Apristurus nakayai (Carcharhiniformes: Pentanchidae) from the South China Sea

diagnosis

Diagnosis. Pre-outer nostril length 4.2 – 4.9 % TL; upper labial furrows longer than the lower furrows; first dorsal fin smaller than second dorsal fin; first dorsal-fin origin situated well behind pelvic-fin insertion, at or slightly behind a vertical line through pelvic-fin tip; second dorsal-fin insertion above or just slightly anterior to anal-fin insertion; snout rather long, tip rounded; abdomen very short; pectoral-fin tip at or slightly extending after the midpoint of P 1 - P 2 space; intestinal spiral valves 14 – 16; monospondylous centra 32 – 36; precaudal diplospondylous centra 34 – 37; clasper hook present on the inner margin of exorhipidion; body uniformly brownish black to black; iris shiny white when fresh; maturing size at about 400 mm TL in both sex.

Occurrence of the milk-eye catshark Apristurus nakayai (Carcharhiniformes: Pentanchidae) from the South China Sea

discussion

Remarks. Apristurus nakayai can be assigned to the ‘ brunneus group’ as defined by Nakaya & Sato (1999) by having the following combination of characters: wide and relatively short snouts, pre-outer nostrils length less than 6 % total length TL; intestine spiral valves 13 – 22; and upper labial furrows longer than lower furrows. Within this group, A. nakayai superficially resembles A. platyrhynchus, which also co-occurs in all known distributions of A. nakayai. Both species share the combination of characteristics: abdomen short, space between pectoral and pelvic fins much shorter than anal-fin base length (ceratotrichia); first dorsal fin much smaller than second dorsal fin; and origin of the first dorsal fin situated well behind pelvic-fin base (Iglésias 2012; Nakaya & Kawauchi 2013). Iglésias (2012) found some morphometrical differences between the two species (i. e., pre-branchial length; mouth width; nostril length; distance between origins of dorsal fins; distance between insertions of dorsal fins; and pelvic-fin length). However, when comparing all the known A. nakayai specimens to the data of A. platyrhynchus in Nakaya & Kawauchi (2013), the above morphometrics significantl

Occurrence of the milk-eye catshark Apristurus nakayai (Carcharhiniformes: Pentanchidae) from the South China Sea

distribution

Distribution. Known from western Pacific, including New Caledonia (Iglésias 2012), Papua New Guinea (White et al. 2017; Ebert et al. 2021), and the South China Sea. This species may eventually be found in other regions within the western Pacific.

Occurrence of the milk-eye catshark Apristurus nakayai (Carcharhiniformes: Pentanchidae) from the South China Sea