Dark Shyshark

Reaching no more than 60 cm (24 in) long, the dark shyshark differs from other shysharks in that it is slender-bodied when juvenile and stocky-bodied when adult. Its head is short, wide, and flattened, with a bluntly rounded snout and very large nostrils. The anterior rims of the nostrils bear greatly enlarged lobes of skin, which are fused into a single flap that reaches the mouth; the flap conceals the nasal excurrent openings and a pair of grooves that run between them and the mouth. The large, horizontally oval eyes are equipped with rudimentary nictitating membranes (protective third eyelids), and have strong ridges beneath. The mouth is short but wide and bears furrows at the corners extending onto both jaws. There are 45–83 upper and 47–75 lower tooth rows; each tooth has a long central cusp flanked by a pair of smaller cusplets.

The range of the dark shyshark is restricted to the coastal waters of southern Africa, from north of Lüderitz in southern Namibia to east of the Storms River mouth in the Eastern Cape Province of South Africa. It is abundant, particularly west of Cape Agulhas. This species is a bottom-dweller found close inshore, from the intertidal zone to a depth of 35 m (115 ft). It prefers rocky reefs and kelp forests, but also presumably traverses sandy flats in between patches of more suitable habitat. As this shark is not known to travel long distances, there is likely subpopulation differentiation across parts of its range.

The dark shyshark is a generalist predator whose main food sources are, in descending order of importance, small benthic crustaceans, bony fishes, and molluscs. Larger sharks consume proportionately more crustaceans. Polychaete worms and echinoderms are also taken on occasion, and algae may be swallowed incidentally. This species is preyed upon by the broadnose sevengill shark (Notorynchus cepedianus), and potentially also other large fishes and marine mammals. When threatened, it adopts a characteristic defense posture in which it curls into a ring with its tail over its eyes; this behavior likely makes the shark harder to swallow and is the origin of the common names "shyshark" and "doughnut". In captivity, the whelks Burnupena papyracea and B. lagenaria have been documented piercing the egg cases of this species and extracting the yolk.

The dark shyshark poses no danger to humans and is too small to be of commercial importance. Many are hooked by sport fishers casting from the shore, who regard the shark as a pest and often kill it. It may also be caught by subsistence fishers and in lobster traps and bottom trawls, though not in substantial quantities. This shark occasionally finds its way into the aquarium trade, though there is no direct fishing for this purpose. As the dark shyshark remains common and does not seem heavily threatened by human activity, it has been assessed as Least Concern by the International Union for Conservation of Nature (IUCN). Its small range does raise concerns that an increase in regional fishing pressure or habitat degradation could impact the entire population.