Most fish today belong to the osteichthyan (bony fish) subgroup - ray-fins, or actinopterygians. In these,
the spine-like fin rays, which hold each fin open like the ribs of a fan, emerge directly from the body,
rather than from a fleshy or lobe-like base. However, before the ray-fins developed, there were earlier
groups, including the jawless fish, or agnathans, and the long-extinct placoderms, or 'flat-plated skins'.
Most fish today belong to the osteichthyan (bony fish) subgroup - ray-fins, or actinopterygians. In these, the spine-like fin rays, which hold each fin open like the ribs of a fan, emerge directly from the body, rather than from a fleshy or lobe-like base. However, before the ray-fins developed, there were earlier groups, including the jawless fish, or agnathans, and the long-extinct placoderms, or 'flat-plated skins'.
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