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Elasmobranchii (/ ɪ ˌ l æ z m ə ˈ b r æ ŋ k i aɪ / [6]) is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea).
Elasmobranchii is a subclass that includes the sharks and the rays and skates. Members of the elasmobranchii have no swim bladders, five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is ...
The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. It was thought that the sharks form a polyphyletic group: some sharks are more closely related to rays than they are to some other sharks, [ 21 ] but current molecular studies support monophyly of both groups of sharks and batoids.
They and their close relatives, the sharks, compose the subclass Elasmobranchii. Rays are the largest group of cartilaginous fishes, with well over 600 species in 26 families. Rays are distinguished by their flattened bodies, enlarged pectoral fins that are fused to the head, and gill slits that are placed on their ventral surfaces.
These rays invest a large amount of energy into reproduction and only give birth to a few offspring; however, they give birth on a yearly basis. [3] They use internal fertilization which is the process of the male inserting his claspers into the female's cloaca to fertilize the eggs. [ 3 ]
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Like other elasmobranchii, Greenland sharks have high concentrations of the two nitrogenous compounds urea and trimethylamine N-oxide (TMAO) in their tissues, which increase their buoyancy [53] and function as osmoprotectants. TMAO also counteracts the protein-destabilizing tendencies of urea [54] [55] and deep-water pressure.
Reproduction in this species is aplacental viviparous, with the unborn young sustained by yolk. There is only one known record of a pregnant female, which was gestating 114 embryos; this ranks among the largest known litters from any shark. The young are probably under 40 cm (16 in) long at birth. [7]