Selachimorpha

Selachimorpha is a subclass of cartilaginous fish within the class Chondrichthyes. It includes all modern cartilaginous fishes, with the exception of the holocephalans, which belong to the subclass Holocephali. The name Selachimorpha was coined by the German zoologist Carl H. Eigenmann in 1890.

Selachimorpha is characterized by the presence of paired gill slits, an epiglossal cartilage, and a diphycercal tail. This subclass also includes sharks and rays, which are highly differentiated and distinct orders within Selachimorpha. The majority of cartilaginous fishes belong to the subclass Selachimorpha.

There are about 1,400 species of sharks and rays within the five orders of Elekidoi, Hexanchiformes, Carcharhiniformes, Orectolobiiformes, and Pristoidei, which all belong to Selachimorpha. These groups exhibit wide variations in body shape, size, and behavior, with the majority being marine predators. However, some species are found in brackish or freshwater environments.

Selachimorpha also includes some extinct groups, such as the Mesozoic placocephalids and various post-Triassic shark-like forms. Paleontologists have discovered fossils of these ancient cartilaginous fishes, which belong to various extinct orders within Selachimorpha. Overall, Selachimorpha represents a diverse and widespread group within the phylogenetic classification of Chondrichthyes.