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Chondrichthyes (/ k ɒ n ˈ d r ɪ k θ i iː z /; from Ancient Greek χόνδρος (khóndros) 'cartilage' and ἰχθύς (ikhthús) 'fish') is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage.
Bony fish have jaws and skeletons made of bone rather than cartilage. About 90% of the world's fish species are bony fish. Bony fish also have hard, bony plates called operculum which help them respire and protect their gills, and they often possess a swim bladder which they use for better control of their buoyancy.
The jaws were used in the buccal pump (observable in modern fish and amphibians) that pumps water across the gills of fish or air into the lungs of amphibians. Over evolutionary time, the more familiar use of jaws in feeding was selected for and became a very important function in vertebrates.
In ichthyology the difference between Euteleostomi and Osteichthyes is that the former presents a cladistic view, i.e. that the terrestrial tetrapods evolved from lobe-finned fish (Sarcopterygii). Until recently, the view of most ichthyologists has been that Osteichthyes were paraphyletic and include only bony fishes. [ 8 ]
The nape is bulging with a slight indentation above each eye. The deep, blunt snout also bulges. The front nostril has a flange which is slightly widened to its rear. There is a recumbent spine to the front of the dorsal fin. [5] Like all rabbitfishes, the dorsal fin has 13 spines and 10 soft rays, while the anal fin has 7 spines and 9 soft rays.
Chauliodus species are recognized by their large, fang-like teeth. They are so long that they would pierce the brain of the fish if misaligned. [3]One species of viperfish, C. sloani, have a sampled standard length of 64.0 to 260.0 mm, with a mean SL of 120.3mm.
The drum typically weighs 5–15 lb (2.3–6.8 kg). The world record was caught on Nickajack Lake in Tennessee, and weighed in at 54 lb 8 oz (24.7 kg). [12] The freshwater drum is frequently gray or silvery but may be more bronze or brown colored, common in the Lake Erie population.
Golden-lined spinefoots form schools which decrease in size with the age of the fish and range from 10 to 25 fish in the adults, although they may from aggregations of several thousand fish when spawning. They feed on encrusting algae which they scrape off from beach rock or pavement areas of coral reefs, and on larger leafy algae. [2]