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Hagfish form a class of about 20 species of eel-shaped, slime-producing marine fish. They are the only known living animals that have a skull but no vertebral column. Lampreys form a superclass containing 38 known extant species of jawless fish. [3] The adult lamprey is characterized by a toothed, funnel-like sucking mouth.
The vertebrates include mammals, birds, amphibians, and various classes of fish and reptiles. The fish include the jawless Agnatha, and the jawed Gnathostomata. The jawed fish include both the cartilaginous fish and the bony fish. Bony fish include the lobe-finned fish, which gave rise to the tetrapods, the animals with four
Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. Only about 100 of the 12,000 extant reptile species and subspecies are classed as marine reptiles, including marine iguanas , sea snakes , sea turtles and saltwater crocodiles .
The oldest known animal that may have been an amniote is Casineria (though it may have been a temnospondyl). [35] [36] [37] A series of footprints from the fossil strata of Nova Scotia dated to 315 Ma show typical reptilian toes and imprints of scales. [38] These tracks are attributed to Hylonomus, the oldest unquestionable reptile known. [39]
But it’s possible that the 202 million-year-old reptile, known as an ichthyosaur or “fish lizard,” may have rivaled it in size. ... had the animal not died, it likely would have kept getting ...
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 ...
Sarcopterygii (/ ˌ s ɑːr k ɒ p t ə ˈ r ɪ dʒ i. aɪ /; from Ancient Greek σάρξ (sárx) 'flesh' and πτέρυξ (ptérux) 'wing, fin') — sometimes considered synonymous with Crossopterygii (from Ancient Greek κροσσός (krossós) 'fringe') — is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe ...
The hemipenis is the intromittent organ of Squamata, [4] which is the second largest order of vertebrates with over 9,000 species distributed around the world. They differ from the intromittent organs of most other amniotes such as mammals, archosaurs and turtles that have a single genital tubercle, as squamates have the paired genitalia remaining separate. [5]