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Fishes are a paraphyletic group and for this reason, the class Pisces seen in older reference works is no longer used in formal taxonomy.Traditional classification divides fish into three extant classes (Agnatha, Chondrichthyes, and Osteichthyes), and with extinct forms sometimes classified within those groups, sometimes as their own classes: [1]
Clupeiformes / ˈ k l uː p iː ɪ f ɔːr m iː z / is the order of ray-finned fish that includes the herring family, Clupeidae, and the anchovy family, Engraulidae and sardines. The group includes many of the most important forage and food fish. Clupeiformes are physostomes, which means that their gas bladder has a pneumatic duct connecting ...
Agnatha (/ ˈ æ ɡ n ə θ ə, æ ɡ ˈ n eɪ θ ə /; [3] from Ancient Greek ἀ-(a-) 'without' and γνάθος (gnáthos) 'jaws') is a paraphyletic infraphylum [4] of non-gnathostome vertebrates, or jawless fish, in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct (conodonts, anaspids, and ostracoderms, among others).
Like other fish, sharks extract oxygen from seawater as it passes over their gills. 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.
A fish (pl.: fish or fishes) is an aquatic, anamniotic, gill-bearing vertebrate animal with swimming fins and a hard skull, but lacking limbs with digits.Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians.
Lungfish are freshwater vertebrates belonging to the class Dipnoi. [1] Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton.
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The lancelet is a small, translucent, fish-like animal that is one of the closest living invertebrate relatives of the vertebrates. [ 80 ] [ 81 ] The lancelets were traditionally seen as the sister lineage to the vertebrates ; in turn, these two groups together (sometimes called Notochordata) were considered the sister group to the Tunicata ...