Elasmobranchii
Elasmobranchii
Elasmobranchii (/ɪˌlæzməˈbræŋkii/), also known as elasmobranchs, are a subclass of Chondrichthyes, or cartilaginous fish, that includes the sharks and the rays and skates, and sawfish. The term "Elasmobranchii" is derived from the Greek words "elasmos" (meaning "metal plate") and "branchia" (meaning "gills"), referring to the gill slits on the sides of the head.
Characteristics
Elasmobranchs are characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. They also have several adaptations for living in a marine environment, such as a high concentration of urea in their blood to maintain osmotic balance.
Classification
Elasmobranchii is a subclass within the class Chondrichthyes, which also includes the Holocephali, a group of cartilaginous fish that includes the chimaeras. The Elasmobranchii are divided into two orders: Carcharhiniformes, which includes the sharks, and Rajiformes, which includes the rays and skates.
Evolution
The first elasmobranchs appeared in the fossil record during the Devonian period, over 400 million years ago. They have since evolved into a wide variety of forms, from the small and harmless catsharks to the large and dangerous great white shark.
Conservation
Many species of elasmobranchs are currently threatened by human activities such as overfishing and habitat destruction. Conservation efforts are being made to protect these species, including the establishment of marine protected areas and restrictions on fishing practices.
See also
External links
- Medical encyclopedia article on Elasmobranchii
- Wikipedia's article - Elasmobranchii
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