Author: Gill, 1862
Field Marks:
Stocky, short-tailed scyliorhinid with no labial furrows, an inflatable stomach, and the second dorsal fin much smaller than the first.
Diagnostic Features:
Body not tadpole-shaped, very stout and spindle-shaped, tapering considerably to caudal fin; body firm and thick-skinned, with well-calcified dermal denticles; stomach inflatable with air or water; tail short, length from vent to lower caudal origin between 2/5 to slightly less than 1/2 of snout-vent length. Head very depressed and broad, narrowly rounded and not wedge-shaped in lateral view; head fairly short, between 1/4 to 1/5 to less than 1/5 of total length in adults; snout very short, less than 1/2 of mouth width, thick, and somewhat flattened, bluntly pointed in lateral view; snout not expanded laterally, rounded-parabolic or subangular in dorsoventral view; ampullal pores not greatly enlarged on snout; nostrils not enlarged, with incurrent and excurrent apertures only slightly open to exterior; anterior nasal flaps broadly tringular to elongated and lobate, without barbels, falling slightly anterior to mouth or reaching it; internarial space 1 to 1.7 times the nostril width; nasoral grooves absent; eyes dorsolateral on head, broad subocular ridges present below eyes; mouth broadly arched or angular, very large and long, with lower symphysis usually somewhat behind upper so that upper teeth are well-exposed in ventral view (lower jaw covering upper teeth in C. silasi); labial furrows absent or vestigial; branchial region not greatly enlarged, distance from spiracles to fifth gill slits 1/2 to 2/5 of head length; gills lateral on head. Two dorsal fins present, with the second considerably smaller than the first; origin of first dorsal about over anterior halves of pelvic bases; origin of second dorsal over or slightly posterior to the anal origin; pectoral fins large, but with their widths varying from less to considerably greater than mouth width; inner margins of pelvic fins not fused over claspers in adult males; claspers moderately long and thick to slender and very long, distally rounded, extending 1/2 to 4/5 of their length behind the pelvic fin tips; tanal fin moderately large, but not greatly elongated, subequal to pelvic and first dorsal fins, but much larger than second dorsal, its base length 1.2 to 1.4 times the second dorsal base; origin of anal well behind pelvic bases, and its insertion separated from lower caudal origin by a space 3/4 to 3/5 of anal base; caudal fin short and broad, between a fourth and a fifth of total length in adults. No crests of denticles on the caudal margins; supraorbital crests present on cranium. Colour varying from uniform grey or brown to variegated with obscure darker saddles and blotches, reticulated dark lines, or numerous dark spots in addition to the saddles and blotches.
Remarks:
The present arrangement of Cephaloscyllium is tentative and follows the revision of Springer (1979) with modifications. Scyliorhinus (Halaelurus) silasi Talwar, 1974 was placed by Springer (1979) in Halaelurus, as an apparent synonym of H. quagga, but it is quite evidently a dwarf species of Cephaloscyllium.
Springer (1979) separated Cephaloscyllium isabellum, from New Zealand, from the Australian Cephaloscyllium laticeps by egg-case morphology only (ridged or 'laminated' in the Australian species and smooth in the New Zealand form), but this was done under the assumption that there was only a single species of Cephaloscyllium in Australian waters. New material from Australia under study by the writer and Dr. John Stevens suggests that, apart from the dwarf Cephaloscyllium fasciatum which was lately collected off northwestern Australia, the Australian swellsharks may comprise at least two large-sized species, a highly variegated and spotted species probably referable to C. laticeps, and the broad-blotched unspotted C. nascione with conspicuous light fin margins. There are also some small Australian swellsharks of uncertain species, that feature scattered black spots on a uniform background. The question arises as to whether C. laticeps really differs from C. isabellum by having 'laminated' egg-cases, or if these come from C. nascione or some other species. Whitley (1940) thought that C. laticeps laid smooth eggs, but noted that "Mr H.M. Hale records 'laminated' eggs as having been laid by South Australian specimens in March, 1929". Unfortunately the swellsharks from which the 'laminated' eggs were taken were not described. With uncertainty as to the type of egg laid by C. laticeps, and no morphological differences between this species and C. isabellum, except possibly colour pattern, the separation of these species becomes questionable. They are listed separately in the species accounts below, at least until Australian and New Zealand swellsharks of the isabellum type can be critically compared.
Springer (1979) also synonymized the Japanese C. umbratile and the Taiwanese C. formosanum with C. isabellum. While this may or may not be correct, there is an additional complication in the form of a dwarf swellshark that occurs in the western North Pacific, that has been generally confused with the large C. umbratile (= C. isabellum) but which differs in its simple blotched colour pattern, differently formed anterior nasal flaps, and longer snout. This probably represents an undescribed species, which is not placed in the key below.