Two biology students from the University of Southern Denmark have stumbled upon the mechanism by which starfish remove foreign objects from their bodies – via squeezing the objects along the length of their body cavities and out through the tips of their arms.
The students, Frederik Ekholm Gaardsted Christensen and Trine Bottos Olsen, were originally assigned to tag common starfish (Asterias rubens) individuals so that researchers could identify and study the starfish. This tagging was achieved through injecting passive integrated transponder tags into the starfish’s skin, however the students soon found that the starfish would somehow expel the tags from themselves shortly after.
“Every time we put a tag into a starfish, they rid themselves of the tag within a few days. It came out directly through the skin; the starfish simply pushed it out through the skin at the end of one arm and then went on as if nothing had happened“, the two students explain.
Although it is not uncommon for organisms to possess mechanisms for removing foreign bodies (e.g. how splinters are slowly pushed out by the body), deeply penetrating items cannot usually be removed so easily. The fact that the starfish individuals could rid themselves of these tags was intriguing as the body cavity of starfish houses a range of organs (similar to humans) that the tag would have to be manoeuvred around on it’s journey to the arm tip and out of the body.
Through the tracking of magnets injected into starfish, the students found that the movements of the foreign item on it’s way to the arm tip seem to be haphazard rather than directed. They also calculated that the starfish would eliminate the objects at a rate of approximately 10% per day.
Previous research has documented that starfish are able to regenerate whole limbs and organs. A starfish that has the ability to regenerate amputated limbs must first undergo a repair phase to heal the exposed wound. Once the wound is healed, the sea star can begin to generate new cells, which in turn, sparks new growth. Regeneration can take anywhere from several months to years. Cell proliferation that results in the growth of the new limb occurs in the final phase. However the ability to eliminate deeply embedded foreign bodies has never before been demonstrated in any organism and this surprising discovery allows an insight into how certain animals are able to quickly heal themselves.
Watch the below video to see the starfish eliminating the foreign objects from their bodies.
Olsen, T. B., Christensen, F. E. G., Lundgreen, K., Dunn, P. H., & Levitis, D. A. (2015). Coelomic Transport and Clearance of Durable Foreign Bodies by Starfish (Asterias rubens). The Biological Bulletin, 228(2), 156-162.