Subclass in Chondrichthyes (cartilaginous fishes) that include shark (Euselachii) and of skate and rays (Batoidei). Other subclasses in Chondrichthyes, according to the traditional classification, is Holocephali (chimaera, or ratfishes). It is possible that the two groups appeared independently during the Silurian or early Devonian are a group of extinct armored fishes, Placodermi. Elasmobranchs are distinguished by separate openings gill, amphistylic or hyostylic jaw suspension and indra ampullae (from Lorenzini) in the region of the head. Characters with holocephalans stops between lines calcified cartilaginous endoskeleton placoid scales of retention mechanism of urea, clasper organs in male for Fertilization is internal, and the absence of water (swim) bladder.