Autotomy and Regeneration

Shedding of body parts in self-defense to avert the attention of the predator-enemy or in any other emergency is a type of autotomy (auto: self, tomy: cutting). The most familiar example of autotomy is a breaking off of the tail in the common house lizard between the chordates, but the phenomenon is far much more common among the non-chordates. You have already seen that this takes place is many echinoderms. The star fishes and brittle stars can cast off their arms that can regenerate into whole animals. An extremely interesting case of autotomy followed by regeneration is found in a polychaete annelid worm termed as Chaetopterus. It lives permanently inside a U-shaped parchment tube in the muddy bottom in shallow sea water. If the anterior end of this worm is pulled by a predator a constriction between 12^th and 13^th segments breaks the body into two pieces. The worm loses its head region to enemy whereas the remaining hind portion is left behind in the U- tube. This hind portion contains the gonads and regenerates the front part needed for normal feeding activity. Chaetopterus has been found to have a remarkable power of regenerating a complete worm from a single isolated body segment that is segment 14.