Editing Echinoderm (section)

===Feeding===

The modes of feeding vary greatly between the different echinoderm taxa. Crinoids and some brittle stars tend to be passive filter-feeders,<ref name="Barnes 997"/><ref>{{harvnb|Ruppert|Fox|Barnes|2004|p=893}}</ref> enmeshing suspended particles from passing water. Most sea urchins are grazers;<ref name="Carefoot Urchins"/> sea cucumbers are deposit feeders;<ref>{{harvnb|Ruppert|Fox|Barnes|2004|p=914}}</ref> and the majority of starfish are active hunters.<ref>{{harvnb|Ruppert|Fox|Barnes|2004|pp=884–885}}</ref>

Crinoids catch food particles using the tube feet on their outspread pinnules, move them into the ambulacral grooves, wrap them in mucus, and convey them to the mouth using the cilia lining the grooves.<ref name="Barnes 997">{{harvnb|Barnes|1982|pp=997–1007}}</ref> The exact dietary requirements of crinoids have been little researched, but in the laboratory, they can be fed with diatoms.<ref>{{harvnb|Carefoot|2011a}}</ref>

[[Basket star]]s are suspension feeders, raising their branched arms to collect [[zooplankton]], while other brittle stars use several methods of feeding. Some are suspension feeders, securing food particles with mucus strands, spines or tube feet on their raised arms. Others are scavengers and detritus feeders. Others again are voracious [[carnivore]]s and able to lasso their waterborne prey with a sudden encirclement by their flexible arms. The limbs then bend under the disc to transfer the food to the jaws and mouth.<ref>{{harvnb|Ruppert|Fox|Barnes|2004|p=893}}</ref>

Many sea urchins feed on algae, often scraping off the thin layer of algae covering the surfaces of rocks with their specialised mouthparts known as Aristotle's lantern. Other species devour smaller organisms, which they may catch with their tube feet. They may also feed on dead fish and other animal matter.<ref name="Carefoot Urchins">{{harvnb|Carefoot|2011b}}</ref> Sand dollars may perform suspension feeding and feed on [[phytoplankton]], detritus, algal pieces and the bacterial layer surrounding grains of sand.<ref>{{harvnb|Carefoot|2011c}}</ref>

Sea cucumbers are often mobile deposit or suspension feeders, using their buccal podia to actively capture food and then stuffing the particles individually into their buccal cavities. Others ingest large quantities of sediment, absorb the organic matter and pass the indigestible mineral particles through their guts. In this way they disturb and process large volumes of substrate, often leaving characteristic ridges of sediment on the seabed. Some sea cucumbers live infaunally in burrows, anterior-end down and anus on the surface, swallowing sediment and passing it through their gut. Other burrowers live anterior-end up and wait for detritus to fall into the entrances of the burrows or rake in debris from the surface nearby with their buccal podia.<ref>{{harvnb|Ruppert|Fox|Barnes|2004|p=914}}</ref>

Nearly all starfish are detritus feeders or carnivores, though a few are suspension feeders. Small fish landing on the upper surface may be captured by pedicilaria and dead animal matter may be scavenged but the main prey items are living invertebrates, mostly bivalve molluscs. To feed on one of these, the starfish moves over it, attaches its tube feet and exerts pressure on the valves by arching its back. When a small gap between the valves is formed, the starfish inserts part of its stomach into the prey, excretes digestive [[enzyme]]s and slowly liquefies the soft body parts. As the [[Adductor muscles (bivalve)|adductor muscle]] of the bivalve relaxes, more stomach is inserted and when digestion is complete, the stomach is returned to its usual position in the starfish with its now liquefied bivalve meal inside it. Other starfish evert the stomach to feed on sponges, sea anemones, corals, detritus and algal films.<ref>{{harvnb|Ruppert|Fox|Barnes|2004|pp=884–885}}</ref>