The spiny dogfish, spurdog, mud shark, or piked dogfish, Squalus acanthias, is one of the best known species of the Squalidae (dogfish) family of sharks, which is part of the Squaliformes order. While these common names may apply to several species, Squalus acanthias is distinguished by having two spines (one anterior to each dorsal fin) and lacks an anal fin. It is found mostly in shallow waters and further offshore in most parts of the world, especially in temperate waters. Spiny dogfish in the northern Pacific Ocean have recently be reevaluated and found to constitute a separate species, now known as "Pacific Spiny Dogfish", Squalus suckleyi.