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In contrast, bony fishes have a single outer bony gill covering called an operculum. Most sharks and rays have five pairs of gill slits, but a few species have 6 or 7 pairs. Shark gill slits lie in a row behind the head. The anterior edge of a gill slit is motile, moving outward to allow water to exit, but closing to prevent reverse flow.
Bonaparte's original definition of Elasmobranchii was effectively identical to modern Chondrichthyes, and was based around gill architecture shared by all 3 living major cartilaginous fish groups. During the 20th century it became standard to exclude chimaeras from Elasmobranchii; along with including many fossil chondrichthyans within the group.
Batoid gill slits lie under the pectoral fins on the underside, whereas a shark's are on the sides of the head. Most batoids have a flat, mantle-like body, with the exception of the guitarfishes and sawfishes , while most sharks have a spindle-shaped body.
Here, the shark pumps blood to its gills via the ventral aorta where it branches into afferent branchial arteries. Gas exchange takes place in the gills and the reoxygenated blood flows into the efferent branchial arteries, which come together to form the dorsal aorta. The blood flows from the dorsal aorta throughout the body.
Ground sharks, like this blacknose shark, have a nictitating membrane which can be drawn over the eye to protect it.. Carcharhiniformes / k ɑːr k ə ˈ r aɪ n ɪ f ɔːr m iː z /, commonly known as ground sharks, are the largest order of sharks, with over 270 species.
The broadnose sevengill shark (Notorynchus cepedianus) is the only extant member of the genus Notorynchus, in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, with the exception of the members of the order Hexanchiformes and the sixgill sawshark. This shark has a large ...
Movements up and down in the water column within a single day ranged from 50 to 385 m. No cyclic diel vertical migration was however observed, the shark having moved smoothly without a defined pattern. [6] The six-gill sharks have the ability to alter their feeding behaviors due to the situation that they are in.
The Bluntnose sixgill shark is one of four shark species that have six gill pairs. Other three are - Frilled shark (Chlamydoselachus anguineus), Bigeyed sixgill shark (Hexanchus nakamurai) [4]) and Atlantic sixgill shark (Hexanchus vitulus) The bluntnose sixgill shark has a large body and long tail. The snout is blunt and wide, and its eyes are ...