page_title: Crinoid
section_title: Feeding
hierarchical_section_title: Crinoid / Biology / Feeding
caption_attribution_description: Podia of a red feather star (Himerometra robustipinna)More about this feather star on the wildfacts sheets on wildsingapore. For a high res version of this photo, please review the details on about using my photos. When making the request, please include this reference: 120123hntd5776
context_page_description: Crinoids are marine animals that make up the class Crinoidea, one of the classes of the phylum Echinodermata, which also includes the starfish, brittle stars, sea urchins and sea cucumbers. Those crinoids which, in their adult form, are attached to the sea bottom by a stalk are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, being members of the largest crinoid order, Comatulida.
  Adult crinoids are characterised by having the mouth located on the upper surface. This is surrounded by feeding arms, and is linked to a U-shaped gut, with the anus being located on the oral disc near the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognised, in most crinoids the five arms are subdivided into ten or more. These have feathery pinnules and are spread wide to gather planktonic particles from the water. At some stage in their life, most crinoids have a stem used to attach themselves to the substrate, but many live attached only as juveniles and become free-swimming as adults.
  There are only about 600 living species of crinoid, but the class was much more abundant and diverse in the past.
context_section_description: Crinoids are passive suspension feeders, filtering plankton and small particles of detritus from the sea water flowing past them with their feather-like arms. The arms are raised to form a fan-shape which is held perpendicular to the current. Mobile crinoids move to perch on rocks, coral heads or other eminences to maximise their feeding opportunities. The food particles are caught by the primary (longest) tube feet, which are fully extended and held erect from the pinnules, forming a food-trapping mesh, while the secondary and tertiary tube feet are involved in manipulating anything encountered. 
  The tube feet are covered with sticky mucus that traps any particles which come in contact. Once they have caught a particle of food, the tube feet flick it into the ambulacral groove, where the cilia propel the mucus and food particles towards the mouth. Lappets at the side of the groove help keep the mucus stream in place. The total length of the food-trapping surface may be very large; the 56 arms of a Japanese sea lily with  24 cm (9 in) arms, have a total length of 80 m (260 ft) including the pinnules. Generally speaking, crinoids living in environments with relatively little plankton have longer and more highly branched arms than those living in food-rich environments.
  The mouth descends into a short oesophagus. There is no true stomach, so the oesophagus connects directly to the intestine, which runs in a single loop right around the inside of the calyx. The intestine often includes numerous diverticulae, some of which may be long or branched. The end of the intestine opens into a short muscular rectum. This ascends towards the anus, which projects from a small conical protuberance at the edge of the tegmen. Faecal matter is formed into large, mucous-cemented pellets which fall onto the tegmen and thence the substrate.
caption: Two arms with pinnules and tube feet outstretched
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