One of the most common deepwater sharks in the northeastern Atlantic Ocean, the velvet belly is found from Iceland and Norway to Gabon and South Africa at a depth of 20–2,490 m (66–8,169 ft).

[2][3] A small shark generally no more than 45 cm (18 in) long, the velvet belly is so named because its black underside is abruptly distinct from the brown coloration on the rest of its body.

[6] Young velvet bellies feed mainly on krill and small bony fish, transitioning to squid and shrimp as they grow larger.

This species exhibits a number of adaptations to living in the deep sea, such as specialized T-cells and liver proteins for dealing with the higher concentrations of heavy metals found there.

The velvet belly was originally described as Squalus spinax by Swedish natural historian Carl Linnaeus, known as the "father of taxonomy", in the 1758 tenth edition of Systema Naturae.

[9] The range of the velvet belly is in the eastern Atlantic, extending from Iceland and Norway to Gabon, including the Mediterranean Sea, the Azores, the Canary Islands, and Cape Verde.

This shark mainly inhabits the outer continental and insular shelves and upper slopes over mud or clay, from close to the bottom to the middle of the water column.

[14] Along with the blackmouth catshark (Galeus melastomus) and the Portuguese dogfish (Centroscymnus coelolepis), the velvet belly is one of the most abundant deep-sea sharks in the northeastern Atlantic.

[17] In the Rockall Trough and the Catalan Sea, large adults are found in deeper waters than juveniles, which may serve to reduce competition between the two groups.

[18] To deal with the higher concentrations of heavy metals in the deep sea, the velvet belly has T-cells in its bloodstream that can identify and mark toxic compounds for elimination.

The velvet belly is an important food of larger fishes such as other sharks; a major predator of this species is the longnosed skate (Dipturus oxyrinchus).

Known internal parasites include the monogenean Squalonchocotyle spinacis, the tapeworms Aporhynchus norvegicus, Lacistorhynchus tenuis, and Phyllobothrium squali, and the nematodes Anisakis simplex and Hysterothylacium aduncum.

[14] As generalist predators, velvet bellies feed on crustaceans (e.g. pasiphaeid shrimp and krill), cephalopods (e.g. ommastrephid squid and sepiolids), and bony fishes (e.g. shads, barracudinas, lanternfishes, and pouts).

[16] The cephalopod diet of adults overlaps with that of the Portuguese dogfish; the latter species may avoid competition with the velvet belly by living in deeper water.

[7][22] The shark's bioluminescence develops before birth; the yolk sac is fluorescent before any photophores have formed, suggesting the mother transfers luminescent materials to her offspring.

[7][17] The IUCN has listed the velvet belly under Least Concern overall, as its population remains stable across much of its range, and it is afforded some protection in the Mediterranean from a 2005 ban on bottom trawling below 1,000 m (3,300 ft).