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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.
Osteichthyes (bone-fish) or bony fishes are a taxonomic group of fish that have bone, as opposed to cartilaginous skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of 45 orders, with over 435 families and 28,000 species. [21] It is the largest class of vertebrates in existence today.
Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal. [58] However, some fish have relatively large brains, most notably mormyrids and sharks, which have brains about as massive relative to body weight as birds and marsupials. [59]
For instance, descendants of the first reptiles include modern reptiles, mammals and birds; the agnathans have given rise to the jawed vertebrates; the bony fishes have given rise to the land vertebrates; the traditional "amphibians" have given rise to the reptiles (traditionally including the synapsids or mammal-like "reptiles"), which in turn ...
Aquatic animals generally conduct gas exchange in water by extracting dissolved oxygen via specialised respiratory organs called gills, through the skin or across enteral mucosae, although some are evolved from terrestrial ancestors that re-adapted to aquatic environments (e.g. marine reptiles and marine mammals), in which case they actually ...
Bony fish have jaws and skeletons made of bone rather than cartilage. About 90% of the world's fish species are bony fish. Bony fish also have hard, bony plates called operculum which help them respire and protect their gills, and they often possess a swim bladder which they use for better control of their buoyancy.
Actinopterygii, members of which are known as ray-finned fishes, is a class or subclass of the bony fishes. The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines ("rays"), as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii ...
Birds feature in the flag designs of 17 countries and numerous subnational entities and territories. [325] Birds are used by nations to symbolise a country's identity and heritage, with 91 countries officially recognising a national bird. Birds of prey are highly represented, though some nations have chosen other species of birds with parrots ...