Biology Of The Starfish

The Starfish are so named because of their star-like appearance. Starfish or sea stars have five arms which are broad based but taper towards the tips. There are short spines along the length of each arm running through their centres with soft white mounds on both sides. The mounds are called papulae. Starfish are either male or female. Most Starfish have different colourings on their aboral and oral surfaces. They are usually coloured orange or brick red on the aboral surface and a paler shade on the other side. Some Starfish are coloured purple on their aboral surface. The average size of the common Starfish is between four to twelve inches in diameter. However, some are known to grow up to twenty inches in diameter. Starfish belong to the biological classification called Echinodermata. They can survive in brackish water.

Biological Distribution of the Starfish

The common Starfish is native to the North Eastern part of the Atlantic Ocean being found along the coasts of the Nordic countries and Western Europe and southwards towards the coast of Senegal. However, they are largely not known to inhabit the Mediterranean Sea.

Feeding and Locomotion of the Starfish

Starfish move by means of small tube feet located underneath their arms.

Starfish are known to feed on Mollusks and other invertebrates found on the Ocean floor. Starfish diet includes barnacles, Mollusks, other Echinoderms, and carrion. It feeds by attaching its stomach to the body of its prey releasing digestive enzymes to dissolve the prey into sufficiently liquid form. When this is achieved, it returns its stomach to the normal position. Starfish have good sense of smell and can detect prey as well as predators which enables them to survive. Starfish are capable of surviving for several months without feeding.

Reproduction of the Starfish

A normal sized Starfish is capable of producing two and a half million eggs. These eggs are externally fertilized by the male in a water column and then drift for almost three months before finally settling down on the floor of the Ocean where they are metamorphosed into juveniles. Orchytophrya stellarium is a parasite of Starfish mostly parasitizing the male species attacking their gonads when ripe and thereby making them infertile. This parasite is a protozoan having ciliates and is therefore described as a ciliate protozoan. Orchyptophra stellarium is a parasite that feeds on different species of Starfish at various times of the year corresponding to their different times of breeding. Research has shown that this parasite is capable of changing the sex ratios of affected populations of Starfish.