Elasmobronchii and Holocephali
Chondrichtyes are a class of cartilaginous fish and contains two subclasses; the Holocephali and the Elasmobronchii. There are about 40 extant species of Holocephali, one example being the ratfish. The main defining feature of the Holocephali is that they have a holostylic jaw suspension. This means that the upper jaw is fused with the braincase. Holocephali are also oviparous and will lay 1-2 eggs at a time. Males will have claspers as well as a frontal tenaculum.
Elasmobrochii includes fish such as sharks, rays and skates. The defining characteristics of Elasmobrochii are their plated gills. These may be on the side of their heads as with sharks, or located ventrally in the rays and skates. This distinction seperates rays and skates into a subgroup called Batoids. Elasmobrachi have placoid scales, that are similar to teeth like structures. In fact, they have a pulp cavity, an enamel like substance that coats them and are even made of dentin, as teeth are. Furthermore, rather than teeth plates, these have polyphydont dentitions.
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