What is an Elasmobranch?

Cartilaginous Fish Including Sharks, Rays, and Skates

Basking shark dorsal fin photo
Basking shark (Cetorhinus maximus) dorsal fin. © Dianna Schulte, Blue Ocean Society for Marine Conservation

 

The term elasmobranch refers to the sharks, rays, and skates, which are cartilaginous fishes. These animals have a skeleton made of cartilage, rather than bone.

These animals are collectively referred to as elasmobranchs because they are in the Class Elasmobranchii. Older classification systems refer to these organisms as Class Chondrichthyes, listing Elasmobranchii as a subclass. The Condrichthyes class includes only one other subclass, the Holocephali (chimaeras), which are unusual fish found in deep water.

According to the World Register of Marine Species (WoRMS), elasmobranch comes from elasmos (Greek for "metal plate") and branchus (Latin for "gill").

  • Pronunciation: ee-LAZ-mo-brank

  • Also Known As: Elasmobranchii

Characteristics of Elasmobranchs

  • Skeleton is made of cartilage rather than bone
  • Five to seven gill openings on each side
  • Rigid dorsal fins (and spines if present)
  • Spiracles to aid in breathing
  • Placoid scales (dermal denticles)
  • The upper jaw of elasmobranchs is not fused to their skull.
  • Elasmobranchs have several rows of teeth which are continually replaced.
  • They don't have swim bladders, but instead their large livers are full of oil to provide buoyancy.
  • Elasmobranchs reproduce sexually with internal fertilization and either bear live young or lay eggs.

Types of Elasmobranchs

There are over 1,000 species in Class Elasmobranchii, including the southern stingray, whale shark, basking shark, and the shortfin mako shark.

The classification of elasmobranchs has undergone revision again and again. Recent molecular studies have found that skates and rays are different enough from all of the sharks that they should be in their own group under elasmobranchs.

Differences between sharks and skates or rays are that sharks swim by moving their tail fin from side to side, while a skate or ray may swim by flapping their large pectoral fins like wings.

Rays are adapted for feeding on the ocean floor.

Sharks are well-known and feared for their ability to kill by biting and tearing. Sawfishes, now endangered, have a long snout with protruding teeth that looks like a chainsaw blade, used for slashing and impaling fish and probling in mud. Electric rays can generate an electric current to stun their prey and for defense.

Stingrays have one or more barbed stingers with venom which they use for self-defense. These can be fatal to humans, as in the case of naturalist Steve Irwin who was killed by a stingray barb in 2006.

The Evolution of Elasmobranchs

The first sharks were seen during the early Devonian period, about 400 million years ago. They diversified during the Carboniferous period but many types went extinct during the big Permian-Triassic extinction. The surviving elasmobranchs then adapted to fill the niches available. During the Jurassic period, skates and rays appeared. Most of the current orders of elasmobranchs trace back to the Cretaceous or earlier.

The classification of elasmobranchs has undergone revision again and again. Recent molecular studies have found that skates and rays in the Batoidea subdivision are different enough from the other types of elasmobranchs that they should be in their own group separate from the sharks.