crab wiki:
>For other uses, see Crab (disambiguation). DromiaceaRaninoidaHeterotremataThoracotremata The term crab is often applied to several different groups of short (nose to tail) decapods with thick exoskeletons, but only members of the Brachyura are true crabs; other taxa, such as hermit crabs, porcelain crabs, king crabs, and horseshoe crabs are, despite superficial similarities, not crabs at all. Hermit crabs, king crabs and porcelain crabs belong to the Anomala and can be distinguished from true crabs by counting the legs - in Anomala, the last pair of pereiopods (walking legs) is hidden inside the carapace and so only four pairs are visible (counting the claws), whereas uninjured true crabs always have five visible pairs.
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fish wiki:
>For other uses, see Fish (disambiguation). Conodonta HyperoartiaPetromyzontidae (lampreys) Pteraspidomorphi (early jawless fish) Thelodonti Anaspida Cephalaspidomorphi (early jawless fish)GaleaspidaPituriaspidaOsteostraci Gnathostomata (jawed vertebrates)PlacodermiChondrichthyes (cartilaginous fish)AcanthodiiOsteichthyes (bony fish) Actinopterygii (ray-finned fish)Sarcopterygii (lobe-finned fish)Actinistia (coelacanths)Dipnoi (lungfish)
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