Chondrichthyes

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Chondrichthyes

A class of vertebrates comprising the cartilaginous, jawed fishes. The Chondrichthyes have traditionally included the subclasses Elasmobranchii (sharks, skates, and rays) and Holocephali (ratfishes). A classification scheme for the Chondrichthyes follows.

  • Class Chondrichthyes
  • Subclass Elasmobranchii
  • Order: Cladoselachii
  • Pleurocanthodii
  • Selachii
  • Batoidea
  • Subclass Holocephali
  • Order Chimaeriformes

A group of Devonian armored fishes, the Placodermi, has usually been regarded as ancestral to the Chondrichthyes, but this derivation is not certain. Another group of primitive jawed fishes called acanthodians, which are considered by many as ancestral to the higher bony fishes, exhibit certain primitive elasmobranch-like features. In any case it is probable that the elasmobranchs and ratfishes arose independently of each other sometime during the Silurian or Early Devonian. See Acanthodii, Placodermi

The most distinctive feature shared by the elasmobranchs and ratfishes is the absence of true bone. In both groups the endoskeleton is cartilaginous; in some cases it may be extensively calcified. Because even calcified cartilage is rarely preserved, the fossil record of the Chondrichthyes is represented mainly by teeth and spines, with only occasional associated skeletons.

Other characteristics of the Chondrichthyes include placoid scales, clasper organs on the pelvic fins of males for internal fertilization, a urea-retention mechanism, and the absence of an air (swim) bladder. Both groups have primarily always been marine predators, although they have repeatedly invaded fresh water throughout their long history. The elasmobranchs have probably always fed as they do today, on other fishes as well as on soft and hard-bodied invertebrates. The ratfishes have most likely concentrated on invertebrates, although modern forms occasionally also feed on smaller fishes. See Ray, Swim bladder

Chondrichthyes

 

a class of fishes that includes two subclasses: Elasmobranchii and Holocephali. The fish have a cartilaginous skeleton fortified by calcification. The scales are placoid. There is a spiral valve in the intestine and an arterial cone in the heart. Many Chondrichthyes have a cloaca. In Elasmobranchii the skull is hyostylic (with a single articulation of the jaw with the skull) or amphistylic (with two such articulations). In Holocephali the skull is autostylic (with the jaw concresced with the skull). In almost all Chondrichthyes insemination is apparently internal. Males have a special copulatory organ, the pterygopodium, which is formed from rays of the ventral fins.

The Chondrichthyes are viviparous or oviparous. The majority are predators. They are predominantly marine fish; only a few Elasmobranchii have adapted to freshwater life. Fossil Chondrichthyes are known from the Devonian.

G. U. LINDBERG

Chondrichthyes

[kän′drik·thē‚ēz]
(vertebrate zoology)
A class of vertebrates comprising the cartilaginous, jawed fishes characterized by the absence of true bone.
References in periodicals archive ?
Despite being an ancient group, we know surprisingly little about the patterns and processes that gave rise to the current diversity of Chondrichthyans," said Dagit.
Some modern chondrichthyans with molariform or pavement-like dentitions, such as horn sharks (Heterdontiformes), bonnethead sharks (Sphyrna tiburo), some rays (Mylobatidae), and chimeras (Holocephali), are durophageous (Dean, 1906; Smith, 1942; Cappetta, 1987; Wilga and Motta, 2000).
Physonemus remains a form genus, of a large chondrichthyan fish of late Paleozoic marine waters, known only from its fin spines.
A survey of molecular variation in a mitochondrial gene among chondrichthyans.
Last & Stevens (1994), in their early compilation of the chondrichthyans of Australia, recognized an additional five undescribed species of Cephaloscyllium.
A comprehensive study of thelodonts and putative chondrichthyans that were collected in the Canadian Arctic Archipelago during the 1994 expedition, as noted above, and in earlier field investigations by one of us (R.
As expected, the demersal fish assemblage in Puget Sound varied substantially across depths and among seasons, but was unusual in that chondrichthyans (spotted raffish and spiny dogfish) made up a majority of the fish biomass.
ningalooensis and its sympatric congeners at the NMP, often occurring within metres of each other, the assemblage is an ideal candidate group for studying habitat specificity and ecological partitioning in chondrichthyans.
The different base structures, both the omalodontid-like and the lingually extended type, have appeared in different groups of chondrichthyans independently.
There are numerous examples in the literature of overexploitation and even extirpation of populations of chondrichthyans because their life history parameters are not understood and/or taken into consideration in management scenarios (Dulvey and Forrest, 2010).