In the thoracic region the intervertebral discs are relatively thin with respect to the vertebral bodies, and together with the presence of the ribs and sternum, their movement is limited.
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.hile 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.
1 Sharks, skates, and rays are collectively termed Elasmobranchs, which are a subclass of Chondrichthyes, or the cartilaginous fishes. 2  The largest shark is the Whale shark which can reach up to 40 feet in length.earn about sharks and opportunities to see them in the wild including whale sharks, hammerheads, and others.