serpulas

A form of serpula — Any of numerous species of tubicolous annelids of the genus Serpula and allied genera of the family Serpulidae that secrete a calcareous tube, usually irregularly contorted, but sometimes spirally coiled, with a wreath of plumelike and often bright-colored gills around its head, and usually an operculum to close the aperture of its tube when it retracts.