Editing Echinoderm (section)

==Regeneration==
{{further|Starfish regeneration}}

[[File:Sea star regenerating legs.jpg|thumb|[[Sunflower seastar|Sunflower star]] regenerating several arms]]

Many echinoderms have great powers of [[regeneration (biology)|regeneration]]. Many species routinely [[autotomy|autotomize]] and regenerate arms and [[viscera]]. Sea cucumbers often discharge parts of their internal organs if they perceive themselves to be threatened, regenerating them over the course of several months. Sea urchins constantly replace spines lost through damage, while sea stars and sea lilies readily lose and regenerate their arms. In most cases, a single severed arm cannot grow into a new starfish in the absence of at least part of the disc.<ref name="Edmondson1935">{{harvnb|Edmondson|1935}}</ref><ref name="McAlaray1987">{{harvnb|McAlary|1993}}</ref><ref name="Hotchkiss2000">{{harvnb|Hotchkiss|2000|loc=last paragraph in review above Analysis}}</ref><ref name="Fisher1925">{{harvnb|Fisher|1925}}</ref> However, in a few species a single arm can survive and develop into a complete individual, and arms are sometimes intentionally detached for the purpose of [[asexual reproduction]].<ref name=McAlaray1987/><ref name=Hotchkiss2000/><ref name=Fisher1925/> During periods when they have lost their digestive tracts, sea cucumbers live off stored nutrients and absorb dissolved organic matter directly from the water.<ref name="dobson1991">{{harvnb|Dobson|Stancyk|Clements|Showman|1991}}</ref>

The regeneration of lost parts involves both [[epimorphosis]] and [[morphallaxis]]. In epimorphosis stem cells, either from a reserve pool or those produced by [[Cellular differentiation#Dedifferentiation|dedifferentiation]], form a [[blastema]] and generate new tissues. Morphallactic regeneration involves the movement and remodelling of existing tissues to replace lost parts.<ref>{{harvnb|Candia-Carnevali|Thorndyke|Matranga|2009}}</ref> Direct [[transdifferentiation]] of one type of tissue to another during tissue replacement is also observed.<ref name="Mashanov2005">{{harvnb|Mashanov|Dolmatov|Heinzeller|2005}}</ref>