We started at Neatorama’s link of a Feather Star swimming, and then found a video of a few of them together, above. From Encyclopedia Britannica:

feather star, any of the 550 living species of crinoid marine invertebrates (class Crinoidea) of the phylum Echinodermata lacking a stalk. The arms, which have feathery fringes and can be used for swimming, usually number five. Feather stars use their grasping “legs” (called cirri) to perch on sponges, corals, or other substrata and feed on drifting microorganisms, trapping them in the sticky arm grooves…

Feather stars occur chiefly on rocky bottoms in shallow water. They are most abundant from the Indian Ocean to Japan, where Tropiometra is the commonest genus. Antedon is the best known genus in the Atlantic.