The spiny dogfishes of the family Squalidae possess a sharp spine in front of each of their two dorsal fins. The most widely known species is Squalus acanthias, called the spiny dogfish, spurdog, or skittle dog. It is abundant along northern Atlantic and Pacific coasts; a closely related, if not identical, form inhabits the southern half of the world. The spiny dogfish is gray, with white spots, and is about 60 to 120 cm (2 to 4 feet) long. Often found in dense schools, it preys on fishes and various invertebrates. It is often a nuisance, as it takes baits and damages fishing nets, but it is edible and also yields liver oil and is ground for fertilizer. Its dorsal fin spines are associated with small venom glands and can cause painful wounds.

The spotted dogfishes of the family Scyliorhinidae include the larger spotted dogfish, or nursehound (Scyliorhinus stellarius), which grows to about 150 cm long, and the lesser spotted dogfish (S. cuniculus), which is about 90 cm long. Both of these common, brown-spotted sharks are caught and sold as food.

The smooth hound, or smooth dogfish (Mustelus canis), is one of the best-known members of the family Triakidae. It is also one of the most common sharks on the American Atlantic coast. It is a slim shark, up to 150 cm long, and is grayish in colour. Like others of its family, it has small teeth, arranged in series, and lacks a well-developed lower tail lobe. It is a bottom dweller and preys on fish and crustaceans.