Author: (Gilbert, 1892)
A tadpole-shaped catshark that is "all head", as suggested by its scientific name, with expanded gill region and small slender body and tail; first dorsal origin somewhat in front of pelvic origins, body extremely soft.
Body strikingly tadpole-shaped, head expanded but trunk and tail slender and cylindrical, tapering to caudal fin; body very soft, semigelatinous, and thin-skinned, with weakly calcified dermal denticles; stomach not inflatable; tail short, length from vent to lower caudal origin less than half of snout-vent length. Head enlarged and considerably depressed, narrowly rounded in lateral view and not wedge-shaped; head very long, about 1/3 of total length in adults; snout very short, less than half of mouth width, thick, and flattened, bluntly pointed in lateral view; snout not expanded laterally, broadly rounded in dorsoventral view; ampullal pores not greatly enlarged on snout; nostrils of moderate size, with incurrent and excurrent apertures only partly open to exterior; anterior nasal flaps broadly triangular, without barbels, well separate from each other and falling somewhat anterior to mouth; internarial space about 1 time the nostril width; no nasoral grooves; eyes dorsolateral on head, narrow subocular ridges present below eyes; mouth angular or semiangular, moderately long, with lower symphysis well behind upper so that upper teeth are exposed in ventral view; labial furrows present along both upper and lower jaws, these very short and ending well behind level of upper symphysis of mouth; branchial region greatly enlarged, distance from spiracles to fifth gill slits 3/4 of head length; gill slits lateral on head. Two equal-sized dorsal fins present, origin of first about one-third of its base length in front of the pelvic origins; origin of second dorsal about over the anal origin; pectoral fins small, their width much less than mouth width; inner margins of pelvic fins not fused over claspers in adult males; claspers moderately long, fairly thick and distally pointed, extending well behind the pelvic fin tips; anal fin moderately large, but not greatly elongated, about as large as pelvic and dorsal fins; base length subequal to second dorsal base;origin of anal well behind pelvic bases, and its insertion separated from lower caudal origin by a broad space over half the anal base; caudal fin moderately elongated, slightly less than a fourth of total length in adults. No crest of denticles on the dorsal caudal margin; supraorbital crests absent from cranium. Colour light to dark brown, without a conspicuous colour pattern.
Eastern Pacific: Southern Baja California and Gulf of California, Mexico.
Habitat and Biology:
A little-known, peculiar little shark of the upper continental slope and outermost shelf, on or near bottom at depths from 155 to 927 m; locally abundant in the Gulf of California. The expanded branchial region of this species and its relatives suggest that they are adapted to bottom areas with low dissolved oxygen levels, as is apparently the filetail catshark, Parmaturus xaniurus, and the triakid Iago omanensis.
Oviparous, one of the live-bearing scyliorhinids, with very thin-walled egg-cases that are apparently retained in the uterus until the young hatch; size of litters 2 (one egg and embryo per uterus).
Maximum about 28 cm; adults maturing at about 19 cm, adult males and females up to at least 24 cm, size at birth about 10 cm. Adult Cephalurus species from Peru and Chile reach 26 to 32 cm.
Interest to Fisheries:
Holotype: U.S. National Museum of Natural History, USNM 125094, Z43 mm adult male. Type Locality: Off Clarion Island, Revillagigedo Islands, 18°17.5'N, 114°43.3'W at 841 m depth.