Starfish or sea stars are the fascinating creatures with unique appearance. They are the members of class Asteroidea. Starfish like stars attract us but they are not actually fishes. These marine animals are echinoderms.
There are over 1,800 species of sea stars, that vary in size, shape and color. Starfish contain hard plates made up of calcium carbonate beneath their skin. They contain special cells in skin that provide information about its surroundings.
Unlike fishes starfish use their tiny tube feet to move along. Star fish have water vascular system that is helpful in movement and predation. They pump sea water into the body through a sieve plate or madreporite, and this water fills the tube feet of starfish. So movement occurs by extending the filled tube feet and also muscles within the tube feet retract them. Tube feet also function as respiratory organs and assist in feeding and in sensory perception.
Most of the starfish varieties have five arms. They exhibit radial symmetry (which means that its components are arranged around a central axis in a symmetrical manner). Their mouth lies in the center on the underside. They feed mainly on clams and oysters.
Interesting fact about starfish is their ability to regenerate their lost arm. In few species the cut-off arm can even give rise to new starfish!!! But the regeneration process can take about one year.
These calm, tiny creature look simple but not so easy to care for. Like many marine aquarium inhabitants, starfish also require very specific care and water qualities to remain healthy.