Sharks

Sharks are a group of elasmobranch cartilaginous fishes characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii and are the sister group to the Batomorphi (rays and skates). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts. Shark-like chondrichthyans such as Cladoselache and Doliodus first appeared in the Devonian Period (4

species of fish

sensory structure present in sharks

Galeomorphi is a superorder of sharks. They are sometimes called galea or galean sharks. There are about 300 living species in 23 families. Galean sharks are divided into four orders: the Heterodontiformes, Orectolobiformes, Lamniformes, and Carcharhiniformes. The extinct, enigmatic Synechodontiformes are presently placed by some authors in the galeomorphs, but their taxonomic position still remains uncertain.

thumb|300x300px|Embryonic oophagy occurs in shortfin mako. Oophagy ( ) or ovophagy, literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek (, "egg") and classical Greek (, "to eat"). In contrast, adelphophagy is the cannibalism of a multi-celled embryo.

teeth of a shark

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Squalomorphi is a superorder of sharks, generally characterized by lacking traits such as an anal fin, nictitating membrane, or suborbital shelves in the cranium. Squalomorphs are also called squalea, or squaleans. There are about 163 living species in 11 families. Squalean sharks are divided into six orders: Echinorhiniformes, Hexanchiformes, Squaliformes, Squatiniformes, Pristiophoriformes and the extinct Protospinaciformes.

part of a shark intestine

mid-Pacific Ocean area noted as a winter and spring habitat of great white sharks

pseudoscientific diet supplement

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