Introduction to the Actinopterygii

This brilliant, spiny, and poisonous lionfish is just one of the world's 20,000 living species of actinopterygians. The name means "ray-finned," for unlike the Chondrichthyes, the fins of the Actinopterygii are webs of skin supported by bony or horny spines. Most actinopterygians have complex skeletons of true bone (sturgeons and paddlefishes are exceptions).

Ray-finned fishes are the dominant aquatic vertebrates today, making up about half of all vertebrate species known. They are found in every aquatic habitat from the abyssal depths of the ocean to freshwater streams and ponds; a few can even crawl on land for short periods of time. Ray-finned fishes constitute a major source of food for millions of people.

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