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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. A modified slit, called a spiracle , lies just behind the eye , which assists the shark with taking in water during respiration and plays a major role in bottom–dwelling sharks.
Spiracle of a bluespotted ribbontail ray, Taeniura lymma. Spiracles (/ ˈ s p ɪr ə k əl, ˈ s p aɪ-/ [1] [2]) are openings on the surface of some animals, which usually lead to respiratory systems. Spiracle of a shark (bighead spurdog, Squalus bucephalus) The spiracle is a small hole behind each eye that opens to the mouth in some fish.
Chimaeras differ from other cartilagenous fish, having lost both the spiracle and the fifth gill slit. The remaining slits are covered by an operculum, developed from the septum of the gill arch in front of the first gill. [6] The shared trait of breathing via gills in bony fish and cartilaginous fish is a famous example of symplesiomorphy.
Unlike other fish, shark gill slits are not covered, but lie in a row behind the head. A modified slit called a spiracle lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active pelagic sharks. [16]
Shark Anatomy (50693674756) The gill slits of a whale shark flaring as it expels water from its pharyngeal cavity. In the shark anatomy image, it depicts the beginning half of the shark, including the gills. The shark gills are especially important and were evolved from the chordate pharyngeal gill slits synapomorphy.
The snout is slender and pointed and the wide mouth, often covered with a fleshy nasal flap, is on the underside of the head. The eyes and well-developed spiracles are located on the top of the head. In most species, the spiracles are large and are the main means of drawing water in for respiration.
The shark is able to breathe with these gills by swimming or staying in a current. The Pacific spiny dogfish also has a special feature called a spiracle. These are gills that are behind the eyes of the shark that give oxygen to the eyes and brain. It is also used to breathe while resting or eating. [20]
The smoothback angelshark is critically endangered. Like the sawback angelshark (Squatina aculeata) found in the same habitat, this species used to be very common.It is most threatened by the intensive fishing in coastal areas and continental shelves by drift nets, gillnets and longlines, which affects most of its range off the African coast.