[23] The scales of some species exhibit bands of uneven seasonal growth called annuli (singular annulus). They breathe using gills to absorb oxygen from the water, although a few, such as the lungfish, can survive in air. The mechanism is complex and not yet understood fully. This bony skull--one of the earliest in the fossil record--is made entirely of little teeth. Such applications intend to enable more efficient movement through fluid mediums such as air, water, and oil. Cephalaspidomorphi, or cephalaspids, were like most contemporary fishes very well armoured. Because of these teeth, the scales have a rough texture. [4] Most fish are also covered in a layer of mucus or slime which can protect against pathogens such as bacteria, fungi, and viruses, and reduce surface resistance when the fish swims.
[20] In this way, ganoid scales are nearly impenetrable and are excellent protection against predation. Ganoid scales are found in the sturgeons, paddlefishes, gars, bowfin, and bichirs. In the marine industry, there is an extremely large market and need for anti-fouling surfaces. [2][3] The same genes involved in tooth and hair development in mammals are also involved in scale development. There is a layer of enamel and even a layer of pulp.
The layer of dentine that was present in the first lobe-finned fish is usually reduced, as in the extant coelacanth, or entirely absent, as in extant lungfish and in the Devonian Eusthenopteron. . Agnatha are fish that have existed for over 470 million years. This space contains collagen fibers. The term scale derives from the Old French "escale", meaning a shell pod or husk.[1]. A defining feature is the lack of paired lateral appendages (fins). Some of the earliest jawless fishes were the ostracoderms (Greek for “bone-skin”).
[35], Unlike bony fish, sharks have a complicated dermal corset made of flexible collagenous fibers arranged as a helical network surrounding their body. "[3] Neil Shubin writes: "Cut the bone of the [ostracoderm] skull open…pop it under a microscope and…you find virtually the same structure as in our teeth. CS1 maint: multiple names: authors list (, evolved independently by different groups, "Fossil fish reveals how jaws evolved - Planet Earth Online", Palaeogeography, Palaeoclimatology, Palaeoecology, Biological Reviews of the Cambridge Philosophical Society, https://en.wikipedia.org/w/index.php?title=Ostracoderm&oldid=953394425, Articles with unsourced statements from April 2015, Creative Commons Attribution-ShareAlike License. He had a hard time classifying them as they did not resemble any living creature. The outermost layer is composed of vitrodentine, a largely inorganic enamel-like substance. Scales typically appear late in the development of fish. Lampreys get some protection from a tough leathery skin. The bony scales of thelodonts, the most abundant form of fossil fish, are well understood. A Dictionary of Zoology . Fish without scales usually evolve alternatives to the protection scales can provide, such as tough leathery skin or bony plates.
These parasitic sea lampreys attach to their lake trout host by suction and use their rough tongues to rasp away flesh in order to feed on the trout’s blood. Some of the earliest jawless fishes were the ostracoderms (which translates to “shell-skin”). This notochord provides support to the hagfish’s body.
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