(Patiria granifera )
(Astropoecten irregularis pontoporaeus)
|Spiny starfishes||(Spinulosa )|
|Dwarf cushion starfish
|Granular cushion starfish
The starfish’s nickname is the sea star. There are about 1,800 living types of sea stars in all the oceans. The north part of the Pacific Ocean has the largest number.
Most species of starfish are 20-30cm wide. A few are only one centimeter. Others can be at the most 60 cm wide. The arms of the starfish are hollow covered with short spines that are called pedicellariae. Pedicellariae are picncherlike organs. There are usually 5 arms. On the lower side of each arm are rows of tube shaped feet. Their feet can allow them to crawl up steep surfaces and hold on. Starfish can also move in any direction. Some of these feet can tips like suckers. If a starfish loses an arm or two it can grow new ones.
Starfish can eat their food in two ways depending upon the species. Some move organic pieces along grooves in the arms into their mouths which are on the bottom of the animal. Other starfish can turn their stomachs out and over their prey and digest them outside their bodies, or, swallow the pray whole. Starfish eat bivalve mollusks, coral polyps and other echinoderms.
There are three groups of starfish called orders.
Phanerozonia have a more rigid body than the other orders. They have suction like tube feet and like to burrow into the ocean bottom. Most of the starfish found in the deepest oceans are members of the Phanerozonia order. Starfish of this order have been found in up to 6000m.
The Spinulosa order of starfish are also known as spiny starfishes. They also have suction-tube feet and groups of spines. A member of this group, the sea bat, usually has webbed arms and can be found from Alaska to Mexico. The very common spiny sun star can have as many as 15 arms.
Forcipulata (cusion starfishes)are starfishes with long stalk like pedicellariae. Their pedicellariae can be used for protection and for food gathering. This group of starfish includes the common shallow water types of starfish that are found around the world. Starfish living in the shallow waters eat clams, oysters and mussels. They use their suction feed to open the animals shell then place their stomachs inside the shell and digest their pray.
One of the world’s largest starfish also belongs to this group. The Pisaser brevispinus can grow up to 65 cm and lives along the western coast of North America. It hunts and eats sand dollars that burrow to escape attack. The sunflower starfish, which can be as wide as 60 cm and have 15 to 24 arms lives along the coastline from Alaska to California.