Editing Crinoid (section)

===Feeding===
[[File:Podia of a red feather star.jpg|thumb|upright|Two arms with pinnules and tube feet outstretched]]
Crinoids are passive [[suspension feeder]]s, 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.<ref name=Ruppert/>

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 [[Metacrinus rotundus|Japanese sea lily]] with  {{convert|24|cm|in|0|abbr=on}} arms, have a total length of {{convert|80|m|ft|-1|abbr=on}} 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.<ref name=Ruppert/>

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 [[Diverticulum|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.<ref name=Ruppert/>