What is Cosmoid scale?
Cosmoid scales are similar to placoid scales and probably evolved from the fusion of placoid scales. They consist of two basal layers of bone, a layer of dentine-like cosmine, and an outer layer of vitrodentine.
Which living vertebrate has Cosmoid scales?
Cosmoid scales, characteristic of extinct lungfishes and not found in any fishes today, are similar to the ganoid scales of living species.
What fishes have Ganoid scales?
Ganoid scales (or modified ganoid scales) are found in fishes such as the bichirs (Polypteridae), Bowfin (Amia calva), paddlefishes (Polyodontidae), gars (Lepisosteidae), and sturgeons (Acipenseridae). Ganoid scales are usually rhomboid in shape and have articulating peg and socket joints between them.
What is Cosmoid?
Definition of cosmoid : relating to or being a ganoid scale that contains a cosmine layer.
Which of the following is Cosmoid scales?
cosmoid scale A type of scale found only in fossil lungfish (Dipneusti), and in Crossopterygii, including the living coelacanth. The thick scales are composed of layers of vitrodentine, followed by cosmine, and finally by layers of vascular and laminated bone underneath.
Do Cosmoid scales grow?
Cosmoid scales increase in size through the growth of the lamellar bone layer.
What are Ganoid scales made of?
bone
Unlike ctenoid or cycloid scales, ganoid scales are comprised of bone. They have a bony basal layer, a layer of dentin (also found in human teeth), and an outer layer of ganoine which is the inorganic bone salt for which these scales are named.
Do Ganoid scales grow?
In most fish, the scales grow as the fish grows, creating a ring pattern similar to that of a tree (ctenoid and cycloid scales). Garfish, paddlefish, and sturgeons have a different type of scale (ganoid) that is made up of thick bony layers that lack growth rings.
What type of fish have Ctenoid scales?
Ctenoid scales are similar to cycloid, except that they have spines or comblike teeth along their free edges; these scales are characteristic of the higher bony fishes—perches and sunfishes, for example. Some fishes, such as catfishes and some eels, have no scales.
Are fish scales made of keratin?
Scales occur on fishes and reptiles. Fish scales are made from more than just keratin. They are often derived from bone in the deeper layers of the skin (the middle section of tissues called the mesoderm), which are named the dermal layer.
What is the difference between cosmoid and ganoid scales?
Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin.
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What is the hard outer layer of ganoid scales called?
In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges),…
What is the difference between cosmoid and placoid scales?
Cosmoid scales, characteristic of extinct lungfishes and not found in any fishes today, are similar to the ganoid scales of living species. Placoid scales (or denticles) are spiny, toothlike projections seen only in cartilaginous fishes.