Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 16 families within the order; they are thought to have a cosmopolitan distribution in tropical and temperate waters worldwide. Sea pens are grouped with the octocorals ("soft corals"), together with sea whips and gorgonians.
Although named after their feather-like appearance reminiscent of antique quill pens, only sea pen species belonging to the suborder Subselliflorae live up to the comparison. Those belonging to the much larger suborder Sessiliflorae lack feathery structures and grow in club-like or radiating forms. The latter suborder includes what are commonly known as sea pansies.
The sea pen fossil record is patchy and disputed by some; while the earliest accepted fossils are known from the Cambrian-aged Burgess Shale (Thaumaptilon), similar fossils from the Ediacaran (ala Charnia) may represent the dawn of sea pens. Precisely what these early fossils are, however, is not decided.
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