Elasmobranchs

Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks (division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by having five to seven pairs of gill slits opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.

The definition of the clade is unclear with respect to fossil chondrichthyans. Some authors consider it as equivalent to Neoselachii (the crown group clade including modern sharks, rays, and all other descendants of their last common ancestor). Other authors use the name Elasmobranchii for a broader branch-based group of all chondrichthyans more closely related to modern sharks and rays than to Holocephali (the clade containing chimaeras and their extinct relatives). Important extinct groups of elasmobranchs sensu lato include the hybodonts (Order Hybodontiformes), xenacanths (order Xenacanthformes) and Ctenacanthiformes. These are also often referred to as "sharks" in reference to their similar anatomy and ecology to modern sharks.