STAR FISH, THE MACROINVERTEBRATE OF SEA

Introduction: Echinoderms are the latest group of macroinvertebrate animals which live exclusively in marine habitat. They are not found in any type of inland water. They have the spiny structures in the outer surface of their body or skin. So they are known as "echinoddermata". Several animals are included under this group like starfish, seacucumber, holothuria etc Among them starfish is very familiar to us. Actually starfish is not the fish. To be a fish the animal must be included under the phylum chordata in which all the animals having the vertebral column are included. But its very funny that starfish sontains neither the vertebral column nor it is a true fish. But still it is popularly known as "starfih." Zoology is a very funny subject although it is a biological study of animals. for example, naming of starfish is not based on any reasonable facts.
Why it is named starfish although its not actually a true fish? It is very interesting question to ask why starfish is named as is. Of course , all the fishes use to live in water. Starfish also lives in water like a fish. Its body is shaped like a star in the sky. So, there are two reasons behind the naming
of starfish. One is it lives in water all the time. And the another reason is that it has the shape like that of the star of sky. So, it is known as starfish.
What is  particular about starfish?  Starfish consists of certain characters which makes it special in the animal world. It consists of a unique system in its body which is not seen in any other groups of animals in the animal world. This is the special type of vascular system in which water circulates in its body. This system is known as "water vascular system". This system is scientifically known as ambulacral system. Another unique structure of its body is the presence of tub e like feet in the body which are called tube feet. They are the legs or locomotary organs of starfish which help in the movement.