CLASSIFICATION OF ASTERIAS (STARFISH)
KINGDOM :- ANIMALIA (Multicellular eukaryotic organisms)
PHYLUM :- ECHINODERMATA (Coelomate, pentaradiate and spiny skinned animals with vascular system.)
SUB-PHYLUM :- ELEUTHEROZOA (Non-pedicellate and free-living.)
CLASS :- ASTEROIDEA (Central disc and arms fused.)
ORDER :- FORCIPULATIDA (Forcipulate and pedicellate pedicellariae.)
FAMILY :- ASTERIIDAE
GENUS :- Asterias (Starfish)
It is distributed in shallow water in North temperate seas and especially abundant and reaching large size on the North Atlantic coast. It is specially found in India and U. S. A.
HABIT AND HABITAT
Asterias is a marine form, found below 200 fathoms on most of the eastern seashore.
GENERAL CHARACTERSTICS OF ASTERIAS (STARFISH)
- Commonly called as starfish or sea star.
- Members are radially symmetrical, free living and star shaped and hence called as starfishes or sea stars.
- Body is radially symmetrical, star-shaped and pentagonal.
- Body or central disc of the animal is distinguished into downwardly directed oral (mouth) and upwardly directed aboral surfaces.
- Central disc is continued into 5 arms.
- Aboral surface is pink and contains conical spines allover and asymmetrical sub-pentagonal madreporite plate in inter-radial position. The finger-like semi-transparent branchiae and pedicellariae are also present on aboral surface.
- Terminal tube feet are photosensitive.
- Oral surface contains central actinostome or mouth, from which five ambulacral grooves extend, one in each arm. The open ambulacral groove accommodates a large number of podia or tube feet.
- Water vascular system is well developed. Tube feet usually terminate in suckers.
- Skeleton consists partly of a mesh work of ossicles and partly of a series of closely set, discrete plates.
- Pedicellariae are usually present and may be of more than one kind.
- Sexes are separate. Fertilization is external.
- The larva is typically a bipinnaria developing into a brachiolaria before metamorphosis into adult.
- These starfish have planktonic larvae.
- The exoskeleton also presents some diagnostic characters, such as the dorsal plates bearing only a single spine in their centre.
The animal contains conical spines and all above features, hence it is Astrias.