User:Aaj1235/Starfish regeneration

Autotomy is understood to serve a defensive function in starfish. While arms can be pulled off the starfish body by predators, the starfish can choose to shed its arm in order to evade danger. If the detached limb is eaten or extremely damaged, bidirectional regeneration is unlikely. There are two ways a starfish can lose its limbs from predators. The loss of limbs includes losing an entire limb or multiple from large prey, or flesh being eaten away by smaller prey. Large prey can eat the starfish whole, whereas smaller prey will turn over a starfish and eat at their soft flesh. Although it is unlikely for bidirectional regeneration, the original starfish can regenerate its lost arm or arms through unidirectional regeneration.

The arm regenerative process of all starfish species studied to date can be subdivided into three distinct phases: a repair phase, an early regenerative phase, and an advanced regenerative phase. Although diversity exists among starfish in terms of their physiology, morphology, and amputation susceptibility, a generalized regenerative process can be appreciated. Throughout the regeneration process, the coelomic epithelium is vital. This is a tissue that plays a large role in the formation of new limbs and new organs.

This replication and delocalization of vital organs makes starfish especially resilient to the loss of appendages. In addition to being able to replicate organs, starfish are also capable of regenerating neuron cells. Other cells that are left over from the injury are able to become neural cells and take up functions they would not normally do. Following injury or amputation, a star fish can survive with its remaining organ copies during the period of regeneration, which ranges from a few months to over a year.

Starfish sexually reproduce through spawning, meaning that sex cells (eggs and sperm) are released into the water and fertilized outside of the body. Each arm contains gonads that swell with eggs and sperm in female and male starfish, respectively. Early observations of Labidiaster starfish found that autotomized arms were swollen with mature eggs, suggesting that autotomy may be utilized for sexual propagation. Under this theory, starfish shed their arms in order to increase the range of egg dispersion and thus increase the possibility of eggs being fertilized by neighboring male starfish. Once the egg has been fertilized a blastula is formed. After the formation of the blastula cilia is produced on the cell allowing the cell to move through the water. When the cell later turns into larva the starfish larva will start to produce its organs, before turning into an adult starfish. The host starfish then regenerates the lost arm through unidirectional regeneration. This theory is challenged by two findings in Lamarck starfish. The first being that very young Lamarck starfish with underdeveloped gonads exhibit autonomy, and the second being that in Hawaii, Lamarck starfish shed arms throughout the year irrespective of spawning season.