Starfish have amazing powers of regeneration. If they lose an arm, they will re-grow it! Some can even re-grow a whole new body from a single arm. Starfish are among the most familiar of marine animals and possess a number of widely known traits, such as regeneration and feeding on mussels. Starfish possess a wide diversity of body forms and feeding methods. The extent that Asteroidea can regenerate varies with individual species. Starfish typically have five rays or arms, which radiate from a central disk. However, several species frequently have six or more arms. Several asteroid groups, such as the Solasteridae, have 10-15 arms whereas some species, such as the Antarctic Labidiaster annulatus can have up to 50. It is not unusual for species that typically have five-rays to exceptionally possess six or more rays due to developmental abnormalities.
The starfish bodies of starfish are composed of calcium carbonate components, known as ossicles. These form the endoskeleton, which takes on a variety of forms that are externally expressed as a variety of structures, such as spines and granules. The architecture and individual shape/form of these plates which often occur in specific patterns or series, as well as their location are the source of morphological data used to classify the different groups within the Asteroidea. Several groups of asteroids, including the Valvatacea but especially the Forcipulatacea possess small bear-trap or valve-like structures known as pedicellariae. These can occur widely over the body surface. In forcipulate asteroids, such as Asterias or Pisaster, pedicellariae occur in pom-pom like tufts at the base of each spine, whereas in goniasterids, such as Hippasteria, pedicellariae are scattered over the body surface. Although the full range of function for these structures is unknown, some are thought to act as defense where others have been observed to aid in feeding.
Starfish belong to a group of animals called ‘Echinoderms’ which means spiny skinned (echino- spiny and derm-skin). Their body is covered in plates. These plates can be large or small, soft or spiky.
Flat with arms
Starfish have a flattened body with 5 or more arms extending from a central disc. They have no bones, no heart, no brain and no eyes. Their mouth is under their body and their bottom is on top.
Beneath each arm, starfish have rows of up to 200 ‘tube feet’. To move starfish pump water in and out of their feet. Feet come in different shapes and each shape is suited to where the starfish lives. To cling tightly to rocks reef starfish have suckers on the end of their feet. Sand starfish have pointed feet to help them dig.
To eat mussels and oysters, starfish use their tube feet to open the shells. They then push their stomach out of their body, into the shell and onto their food. Once it has soaked up its food the starfish pulls its stomach back in!