Starfish

Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "sea star" essentially refer to members of the Class Asteroidea. However, common usage frequently finds "starfish" and "sea star" also applied to ophiuroids which are correctly referred to as "brittle stars" or "basket stars".

There are 2,000 living species of starfish that occur in all the world's oceans, including the Atlantic, Pacific, Indian as well as in the Arctic and the Southern Ocean regions. Starfish occur across a broad depth range from the intertidal to abyssal depths (6000 m).

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. Broadly speaking, starfish are opportunistic feeders, with several species having specialized feeding behavior, including suspension feeding and specialized predation on specific prey.

The Asteroidea occupy several important roles throughout ecology and biology. Sea stars, such as the Ochre sea star (Pisaster ochraceus) have become widely known as the example of the keystone species concept in ecology. The tropical Crown of Thorns starfish (Acanthaster planci) are voracious predators of coral throughout the Indo-Pacific region. Other starfish, such as members of the Asterinidae are frequently used in developmental biology.

More about Starfish

Starfish, or sea stars (a less confusing designation, since they are only very distantly related to fish), are marine invertebrates belonging to the kingdom animalia, phylum Echinodermata, and class Asteroidea, of which there are over 1800 known species. The names sea star and starfish also are (incorrectly) used for the closely related brittle stars, which make up the class Ophiuroidea.

Characteristics of sea stars include that they exhibit a superficially radial symmetry, since they typically have five or more "arms" which radiate from an indistinct disk (pentaradial symmetry), and tend to be covered in spines. Like other echinoderms, starfish possess an endoskeleton, but do not rely on it for support and locomotion, instead using a hydraulic water vascular system that functions via many projections called tube feet, located on the ventral surface of the starfish's arms.

Starfish are an essential part of marine food chains, being eaten as larvae, and becoming voracious predators upon reaching adulthood, with their diet including mollusks and other marine organisms. They even are able to evert their stomach in order to pull apart and digest their shelled prey. For humans, they are a source of aesthetic joy and their remarkable characteristics—movement based on a hydraulics system, ability to regenerate lost limbs and evert their stomach—add to the wonder of nature. Some starfish also are captured, dried out, and turned into popular souvenirs or decorations.

While starfish can reproduce sexually, if an arm of the starfish is severed from the body and it contains a portion of the central nerve ring, then another starfish can regrow from the severed portion. Lack of knowledge of this capacity increased the role of starfish as pests to commercial clam and oyster beds when fisherman, in an effort to get rid of these predators, would cut them up and throw them back into the ocean.