Most crinoids, often referred to as 'sea lilies', are sessile creatures with calcified skeletons and sometimes stalks which attach to hard substrates. Some however, are known to be stemless and swim with help from their many arms. Their arms are covered in feathery pinnules which help filter particles and microorganisms out of the water column. The central mass is called the calyx where the mouth of the organism can be found.
Breimer, A., 1978. General Features of Crinoidea in Moore, R. C., ed., Treatise on Invertebrate Paleontology, Part T, Echinodermata 2, Volume 1. The University of Kansas and Geological Society of America. 401 pp.