Thursday, October 20, 2011

Life of Starfish

Life of Sea | Starfish (Asteroidea) | Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "Sea Star" essentially concern the members of the class Asteroidea. However, common usage is often called "starfish" and "Sea Star" also applies to ophiuroids that correctly referred to as "brittle stars" or "basket stars". There are about 1,800 living species of  Starfish that occur in all oceans of the world, including the Atlantic, Pacific, Indian and in the Arctic and Southern Ocean regions.

Starfish can be found in rock pools and on beaches. The habitat ranges and consists of coarse gravel and rock and Shelly. Abundance increases strongly on the growth of algae carpets in comparison with fine sand. The common  Starfish is unusual in that it tolerates estuarine habitats.  Starfish occur over a wide depth range from the intertidal to abyssal depths. 

Scientific classification
Kingdom:     Animalia
Phylum:     Echinodermata
Subphylum:     Asterozoa
Class:     Asteroidea, De Blainville, 1830

Although the 
Starfish live under water and are commonly called "starfish," they are not fish. They do not have gills, scales or fins like fish do, and they are very different fish. As the fish continued to move their tails,  Starfish have tiny tube feet to help them move along (see more on this below). While the five-armed variants of the sea star are the best known, not all  Starfish have five arms.For example, the Sun star is up to 40 arms.

Starfish are very slowly moved over the seabed by their tiny tube feet. Tube feet can produce strong suction, fixing the  Starfish in place and making it difficult for a predator to eat the whole organism. Occasionally starfish can be seen with missing limbs. This is not a great loss to a starfish as they can grow back. Sometimes common  Starfish with six or more limbs are seen, this is a result of the starfish accidentally growing two parts to replace a loss.  Starfish are active carnivores, and catch well. They hunt live bivalve molluscs by forcing their shells open with their tube feet. The stomach Everts over or into the prey so that the liquid can be easily digested. In shallow waters dense congregations of starfish can be found on an expanse of several kilometers.
  Amazingly,  Starfish can regenerate lost arms. This is useful when the sea star is threatened by a predator - it can drop an arm and get away.  Starfish house most of their vital organs in their arms, so that some can even regenerate a whole new sea star from only one arm and part of the central star disc. It will not happen too quickly, though. It takes about one year for an arm to grow back. 
Depending on the species, a  Starfish feels leathery skin, or slightly prickly.  Starfish have a hard coating on its upper side, which consists of plates of calcium carbonate with small spines on their surface. Starfish spines used for protection against predators, the birds, fish and sea otters to take. Although they can not see as well as we do, sea stars have an eye spot at the end of each arm. This is a very simple eye that looks like a red spot. The eye does not see much detail, but can sense light and dark.

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