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The Cypriniformes are an order of ray-finned fish, including the carps, minnows, loaches and relatives. This order contains 5-6 families, over 320 genera, and more than 3,250 species, with new species being described every few months or so, and new genera being recognized regularly. They are most diverse in southeastern Asia, but are entirely absent from Australia and South America.
Their closest living relatives are the Characiformes (characins and allies), the Gymnotiformes (electric eel and American knifefishes) and the Siluriformes (catfishes).
Like other orders of the Ostariophysi, the cypriniformes possess a Weberian apparatus. However, they differ from most of their relatives in having only a dorsal fin on their back; most other Ostariophysi have a small fleshy adipose fin behind the dorsal fin. Further differences are the Cypriniformes' kinethmoid and the lack of teeth in the mouth. Instead, they have convergent structures called pharyngeal teeth in the throat. While other groups of fish, such as cichlids, also possess pharyngeal teeth, the cypriniformes' teeth grind against a chewing pad on the base of the skull, instead of an upper pharyngeal jaw.
The most notable family placed here is the Cyprinidae (carps and minnows) which make up two-thirds of the order's diversity. This is one of the largest families of fish, and is widely distributed across Africa, Eurasia, and North America. Most species are strictly freshwater inhabitants, but a considerable number are found in brackish water, such as roach and bream. At least one species is found in the sea, the Pacific Redfin, Tribolodon brandtii.. Brackish water and marine cyprinids are invariably anadromous, swimming upstream into rivers to spawn. The enigmatic mountain carps are a small group of mountain stream fishes confined to Southeast Asia. Sometimes separated as family Psilorhynchidae, they seem to be specially-adapted Cyprinidae.
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