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Cosmine was first described in the Osteolepiform Megalichthys hibberti by Williamson in 1849, in a purely descriptive, pre-Darwinian, non-evolutionary framework. [4] Goodrich [5] expanded on Williamson's descriptions, hypothesizing a transition from a monoodontode scale (like a chondryicthian placoid scale) to a complex polyodontode scale through fusion of discrete units.
A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as well as possible hydrodynamic advantages.
Reptile scale types include: cycloid, granular (which appear bumpy), and keeled (which have a center ridge). Scales usually vary in size, the stouter, larger scales cover parts that are often exposed to physical stress (usually the feet, tail and head), while scales are small around the joints for flexibility.
Ichthyosis (also named fish scale disease) [1] is a family of genetic skin disorders characterized by dry, thickened, scaly skin. [2] The more than 20 types of ichthyosis range in severity of symptoms, outward appearance, underlying genetic cause and mode of inheritance (e.g., dominant, recessive, autosomal or X-linked). [3]
Ganoine or ganoin is a glassy, often multi-layered mineralized tissue that covers the scales, cranial bones and fin rays in some non-teleost ray-finned fishes, [1] such as gars and bichirs, as well as lobe-finned coelacanths. [2] It is composed of rod-like, pseudoprismatic apatite crystallites, with less than 5% of organic matter. [3]
This process continues, so that each generation is half (or hemi-) clonal on the mother's side and has half new genetic material from the father's side. [60] [64] This form of reproduction is seen in some live-bearing fish of the genus Poeciliopsis [62] [65] as well as in some of the Pelophylax spp. ("green frogs" or "waterfrogs"):
When the two varieties were cross-bred the eggs were infertile suggesting reproductive isolation. [239] [241] The genetic data indicates that the molestus form in the London Underground mosquito appears to have a common ancestry, rather than the population at each station being related to the nearest aboveground population (i.e. the pipiens ...
Aristotle (ca. 340 B.C.) may have been the first scientist to speculate on the use of hard parts of fishes to determine age, stating in Historica Animalium that “the age of a scaly fish may be told by the size and hardness of its scales.” [4] However, it was not until the development of the microscope that more detailed studies were performed on the structure of scales. [5]