Starfish remove foreign bodies through their skin
It has long been known that starfish are capable of regenerating whole limbs and organs. A new starfish behaviour observed in Asterias rubens provides an insight into how they are able to heal themselves quickly. This new discovery has never been demonstrated in any organism before.
The newly identified behaviour was observed by two biology students Frederik Ekholm Gaardsted Christensen and Trine Bottos Olsen from the University of Southern Denmark when they were asked to tag starfish. These tags were injected into the arm of starfish just like veterinarian tags in dogs and cats to enable researchers to easily identify the individuals.
However, after just a few days the starfish were able to remove the tags by forcefully ejecting them through the body wall at the distal tip of an arm. Basically the starfish were observed pushing the tags directly through the skin. Interestingly, the starfish did not attempt to push the tag out through the hole created by the injection.
Magnets and ultrasound images were used to locate the movement of the embedded foreign bodies. By tracking the magnets injected into the starfish, the tag appeared to wander randomly between the organs before ultimately being squeezed along the length of their body cavities probably by constrictions of the body wall and then out through their arm tips. The authors of the paper estimate that the foreign bodies were eliminated at a rate of approximately 10 percent per day.
This type of behaviour has, until now, never been described before in the scientific literature. Many species are capable of removing foreign bodies from their bodies in certain conditions. However, they are unable to do so when the object becomes lodged deep within their bodies and so the only option to remove the object is via surgery.
Starfish often loose whole limbs or suffer substantial wounds. As a result, researchers believe they may be more susceptible to foreign bodies ending up inside their bodies and so have developed this mechanism which would certainly be useful for evicting large parasites and bits of coral, sand or rock introduced by injuries. The latest discovery leads to questions such as: How large an object can a starfish expel? Why use the arm tips and what other animals can use this mechanism?
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