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Regions of a Chondrichthyes brain colored and labeled on dissected skate. The rostral end of the skate is to the right. In chondrichthyans, the nervous system is composed of a small brain, 8–10 pairs of cranial nerves, and a spinal cord with spinal nerves. [11] They have several sensory organs which provide information to be processed.
The phylogenetic classification of bony fishes is a phylogenetic classification of bony fishes and is based on phylogenies inferred using molecular and genomic data for nearly 2000 fishes. [ 1 ] [ 2 ] [ 3 ] The first version was published in 2013 and resolved 66 orders. [ 2 ]
Fishes are a paraphyletic group and for this reason, the class Pisces seen in older reference works is no longer used in formal taxonomy.Traditional classification divides fish into three extant classes (Agnatha, Chondrichthyes, and Osteichthyes), and with extinct forms sometimes classified within those groups, sometimes as their own classes: [1]
Chimaeras (Chimaeriformes) are cartilaginous fish belonging to the subclass Holocephali, in the class Chondrichthyes, distantly related to sharks and rays (Elasmobranchii). Listed below are extant species of chimaera. Chimaera diversity is spread across more than 50 species in six genera, three families, and one order.
Elasmobranchii is one of the two subclasses of cartilaginous fish in the class Chondrichthyes, the other being Holocephali . Members of the elasmobranchii subclass 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 ...
Several fossil species are attributed to Chimaera, but only two are confidently assignable to it.These two are C. seymourensis from the Late-Eocene La Meseta Formation on Seymour Island off the coast of the Antarctic Peninsula, [6] [7] and C. pliocenica from the Pliocene of Tuscany, Italy. [7]
The idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being).Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).
Chimaeras are soft-bodied, shark-like fish with bulky heads and long, tapered tails; measured from the tail, they can grow up to 150 cm (4.9 ft) in length. Like other members of the class Chondrichthyes, chimaera skeletons are entirely cartilaginous, or composed of cartilage.