- Norwegian: sjøfjær
Sea pens are all colonial, marine species. They have earned the name because many species, but certainly not all, look like an antique quill pen. There are multiple polyps on each colony, and each polyp has eight arms, as one should expect from a member of the subclass Octocorallia. In contrast to other octocorals, the polyps of sea pens specialize to perform specific tasks, like feeding or reproduction. All colonies have a central stem.
There are two suborders and 14 families of sea pens. Members of some families look like the traditional quill pen, while members of others lack the feathery structure and may take a club-shaped or radial form.