Author: Garman, 1913
Field Marks:
Scyliorhinids with "the Apristurus look" - Long laterally expanded snout and head, enlarged nostrils with reduced anterior nasal flaps, very long labial furrows, small rear-sited, spineless dorsal fins, very large, elongated anal fin separated from elongated caudal by a notch only, and uniform coloration.
Diagnostic Features:
Body not tadpole-shaped, stocky and more or less compressed, increasing in height up to the pectoral and trunk region and tapering posteriorly; body very soft and flabby, with thin skin and weakly calcified dermal denticles; stomach not inflatable; tail short, length from vent to lower caudal origin about 2/5 to 3/5 of snout-vent length. Head greatly depressed, pointed and wedge-shaped in lateral view, rather elongated, but usually slightly less than 1/4 of total length in adults; snout elongated, about equal to mouth width or greater, greatly flattened, narrow and pointed in lateral view; snout expanded laterally, narrowly spade-shaped to broadly spatulate and usually more or less bell-shaped in dorsoventral view; ampullal pores enlarged and prominent on snout; nostrils more or less enlarged, with incurrent and excurrent apertures broadly open to exterior; anterior nasal flaps reduced to angular lobes, without barbels, widely separate from each other and falling far anterior to mouth; internarial space 0.8 to 1.7 times the nostril width; no nasoral grooves; eyes dorsolateral on head, broad subocular ridges present below eyes; mouth angular or broadly arched, 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 long and reaching nearly or quite to level of upper symphysis of mouth; branchial region not greatly enlarged, distance from spiracles to fifth gill slits less than half head length; gill slits lateral on head. Two dorsal fins present, equalsized or with the second dorsal larger than the first; origin of first dorsal varying from over the pelvic midbases to over the pelvic free rear tips; origin of second dorsal about over or slightly behind the anal midbase, anal fin enlarged and more or less elongated, larger than pelvic and dorsal fins, base length at least twice second dorsal base; origin of anal just behind pelvic bases, and insertion separated from lower caudal origin by a narrow notch; pectoral fins variable in size, their width less to greater than mouth width; inner margins of pelvic fins not fused over claspers in adult males; claspers short, thick, and distally pointed, not extending more than 2/3 of their lengths behind the pelvic fin tips and sometimes not extending past their tips. Caudal fin more or less elongated, over a fifth and often over a fourth of total length. A crest of enlarged denticles absent or variably developed on the dorsal caudal margin; supraorbital crests absent from cranium. No colour pattern, uniformly jet black, brownish-black, brown, pinkish or whitish.
Remarks:
This is one of the largest and perhaps least known of shark genera, having some 25 described species and several unnamed taxa. Springer (1966, 1979) recently revised the genus while Nakaya (1975) reviewed the Japanese species. Despite their efforts, several species are of uncertain validity, with over a third of the species known from the holotypes only, at least four species having the holotypes lost, and less than a third of the species known from modest to good series of specimens. Judging from the frequency that new species are discovered, the wide geographic range of the genus, and the paucity of knowledge of slope faunas in many areas of the world, this may eventually become the largest genus of sharks.
The present treatment of Apristurus contains much new data and differs from Springer's (1979) revision in a number of ways; but most importantly it includes three species placed by him in separate genera. A. spongiceps was placed by Springer in the genus Parapristurus, raised in rank from a subgenus proposed by Fowler (1934). It was primarily distinguished from Apristurus by its pleated gills and throat, but although no Apristurus have pleats and grooves on their gills, several have them on their throats, including A. manis, A. riveri (photo in Springer, 1979, fig. 18), and a possibly undescribed Galapagos-Peruvian species close to A. stenseni. Also, other species of Apristurus including A. kampae, A. manis, and A. microps approach A. sponuiceps in its unusually stocky body and high rounded fins. The writer prefers to retain Parapristurus in Apristurus, and thinks it may be worthy of subgeneric ranking at best.
Springer's earlier (1966) revision of western Atlantic Apristurus included a species with a crest of enlarged denticles on its caudal fin, which he termed A. profundorum. However, he later (Springer, 1979) noted that two species were confused under this name, the true profundorum without a crest and a new species with a crest. This latter he placed in Parmaturus rather than Apristurus, as P. manis, along with a second new species, P. stenseni, in the new subgenus Compagnoia.
Compagnoia was an anomaly within Parmaturus because although it supposedly agreed with that genus and differed from Apristurus in its supracaudal crest, its members otherwise closely resembled Apristurus species and not typical Parmaturus (such as P. pilosus and P. xaniurus) in their long, laterally expanded snouts and heads, enlarged nostrils, long labial furrows, compressed bodies, long low anal fins separated by a notch from the caudal fin, and long narrow caudal fins. Investigation of the caudal fins of Apristurus species by the writer showed that caudal crests are not confined to manis and stenseni, but are variably developed in A. canutus, A. investigatoris, A. microps, A. parvipinnis, the true A. profundorum, and at least two apparently undescribed species. Rather than placing these species in an increasingly heterogeneous Parmaturus, I prefer to transfer the subgenus Compagnoia to Apristurus, and place manis and stenseni in that genus. Those Apristurus with caudal crests are sufficiently heterogeneous so as not to warrant their inclusion in the subgenus Compagnoia as distinct from all other Apristurus. A. microps and A. profundorum are isolated in the genus and not particularly close to either A. manis or A. stenseni, A. canutus and A. parvipinnis are closest to A. platyrhynchus and A. verweyi, while A. investigatoris is apparently close to A. indicus. A. stenseni appears to be not particularly close to A. manis but forms a species groups or superspecies with A. riveri, A. kampae, a possibly new Galapagos-Peruvian species, a whitish species from the eastern Atlantic (possibly A. atlanticus), and a possibly new dark western Atlantic species. If the subgenus Compagnoia is recognized it would be best utilized for its type alone, the distinctive and isolated A. manis.