Description of Actinopterygii
The Actinopterygii or ray-finned fishes are so called because their fins are webs of skin supported by bony or horny spines (the rays), as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii (lobe-finned fish). The actinopterygian fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the link or connection between these fins and the internal skeleton (e.g., pelvic and pectoral girdles). The actinopterygians are the most speciose class of vertebrates, comprising nearly 96% of the 25,000 species of fish. They are ubiquitous throughout fresh water and marine environments from the deep sea to the highest mountain streams. Extant species can range in size from Paedocypris, at 8 millimetres to the massive Ocean Sunfish, at 2,300 kilograms (5,100 lb), and the long-bodied Oarfish, to at least 11 metres.
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