Systematic position:
Phylum: Echinodermata
Class: Asteroieea
Order: Forcipulata
Genus: Asterias
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea.It is commonly called star fish or seea star. It is present of five or more arms from the central disc.
Habitat: The sea stars are free living marine animals. It is found in all oceans at all depths. It leaves at the bottom.
Habits: Sea stars are nocturnal and carnivorous feedding mainly on crustaceans and molluscs. The commonest food of stae fish are the bivalves. They are dioecious. Fertilization is external. Development is direct and larva stage.
Locomotion: It creeps on substratum with the help of tube feet and swims by snake like movements of arms
Feeding: It is scavenger feed on dead organism.It is omnivorous in feeding.
Reproddduction: It is unisexual or dioecious with no sexual dimorphism. Female is oviparous. Fertilization is external and development is indirect and larva stages.
External characters:
Shape , size and colour : The body of Asterias is star shaped and radial symmetry. It measures 10 to 20 cm in diameter. Its colour is variable ,brown, yellow, pink and purple.
Body parts: Body consists of an indistinct central disc,five arms,rays or branchioles.
Economic importance: It is used as food for fishes.
Morphology: Body is star shaped and is formed of central disc
Arms are long, slender and highly flexible.
Madreporite is present on oral side of central disc.
