Starfish or Starfish-Asterias: classification, characteristics

Starfish or Starfish-Asterias

Introduction of Starfish

Starfish are star-shaped echinoderms, also known as sea stars. These are marine invertebrates and usually have a central disc with five arms attached to it. Some of its other species have more than five arms. Its other species are usually of different colors. It has tube feet on the lower surface of its arms which help them to walk. It has a mouth on the lower surface of the central disc.

Starfish are opportunistic feeders. Its different species have a special feeding behavior. Both types of reproduction are found in them (sexual and asexual). Most species of starfish have the ability to regenerate, which allows them to regenerate severed or damaged parts of their bodies, and sometimes they even drop their arms in defense.

Classification

Kingdom            -         Animalia

Branch                -         Eumetazoa
Division              -         Bilateria

Subdivision         -         Deuterostomia
Section                -         Eucoelomata
Phylum                -        Echinodermata
Subphylum          -        Asterozoa
Class                   -         Asteroidea
Order                   -         Forcipulata

Characteristics

The main characteristics of starfish are as follows-

1. Starfish are found in shallow seas crawling on stones, rocks or bottom mud.
2. Their body is flattened, pentamerous, like a star, in the middle of which a large, but indistinct body mass or central disc is present. Five small conical radial arms emerge from it.
3. Their mouth is in the middle of the ventral surface of the central disc, that is, on the oral surface.
4. In these, the anus is on the upper (aboral) plane of the disc. On the same plane, there is another, bigger hole on which a sieve-like cover called madreporite is present. Sea water enters the vascular system through this hole.
5. They have an ambulacral groove on their oral plane extending from the mouth to the top of each arm. There are rows of small movable and immovable calcareous spines along the edge of these grooves.
6. Here and there in each ambulacral groove there are two rows of small hollow and contractile sucker like tube feet. It helps in locomotion, food intake and respiration.
7. Their skin is firm and leathery. Many calcareous spines, pincer-like pedicellariae and finger-like dermal gills are present on it.
8. There is a large coelom cavity filled with fluid between their body wall and viscera.
9. In their central disc, there is a small alimentary canal that extends between the mouth and the anus.
10. They have a water vascular system associated with tube feet for movement, in which sea water flows through the madreporite.
11. For the circulatory system in their body, the haemal system is present as a part of the body cavity itself.
12. They do not have any special organs for excretion. Their nervous system remains suspended in the skin and sensory organs are also present in the skin and on the top of the arms.
13. These organism are monogamous. Their reproductive system is simple and five pairs of gonads are present in it. There are no accessory genitals and sexual organs in their body. Fertilization and embryonic development take place in sea water. Their life cycle is complicated. In this, three types of larval stages are formed and metamorphosis takes place.
14. They have a very high capacity for regeneration. That is, if their one arm is cut off and separated, then a new arm grows in its place. This is called regeneration.

fun facts- Despite having a fish in the name of a starfish, it is not a real fish.