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Placoid scales cannot grow in size, but rather more scales are added as the fish increases in size. Similar scales can also be found under the head of the denticle herring. The amount of scale coverage is much less in rays. Rhomboidal scales with the properties of both placoid and ganoid scales are suspected to exist in modern jawed fish ...
Placoid Scale. Super Smooth scales (dermal denticles) coat the skin of sharks, rays, and cartilaginous fishes due to the absence of dermal bone. These scales are present in the dermis, which has fibrous connective tissue components, and project through the epidermis, which contains secretory cells and stratified epidermal cells, to the surface.
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.
Ganoid scales are flat, basal-looking scales. Derived from placoid scales, they have a thick coat of enamel, but without the underlying layer of dentin. These scales cover the fish's body with little overlapping. They are typical of gar and bichirs. Cycloid scales are small, oval-shaped scales with growth rings like the rings of a tree. They ...
Extant chondrichthyans range in size from the 10 cm (3.9 in) finless sleeper ray to the over 10 m (33 ft) ... rigid dorsal fins, and small placoid scales. The teeth ...
A large portion of the skate's dorsal body is covered by rough skin made of placoid scales. Placoid scales have a pointed tip that is oriented caudally and are homologous to teeth. Their mouths are located on the underside of the body, with a jaw suspension common to Batoids known as euhyostyly. [11]
The trunk and tail are laterally compressed, while the head region is dorsoventrally compressed. The entire body is covered by an exoskeleton of placoid scales. The mouth is located on the ventral side and is bound on both sides by jaws. It has two rows of homodont or polyphyodont teeth, which are homologous to the placoid scales covering
Scientists are sceptical. Counting growth lines on the scales of fish confined to ponds or bowls is unreliable, since they lay down extra lines. [40] [41] The maximum reliably reported age for a goldfish is 41 years. [42] Atlantic tarpon: One of the longest living sport fish is the Atlantic tarpon, with a reported age of 55 years. [43] [44] [45 ...