Starfish
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Starfish belong to the phylum Echinodermata, class Asteroidea, which consists of roughly 1,500 species (Boyer and Bearzi, 2003; Shine, 2002). They are not fish at all, and should correctly be called sea stars (Shine, 2002). Sea stars are benthic animals, living in every type of marine environment: shallow bays, lagoons, the back and front of reefs, external reefs and deep reefs, and can be found from the Arctic to the Antarctic oceans (Boyer and Bearzi, 2003; Shine, 2002). Like most Echinodermata, sea stars show radial symmetry, with no head or tail, and have a star-shaped body (Boyer and Bearzi, 2003). The symmetry of sea stars is usually pentaradial, with many of the organs repeated in each of arms. Sea stars have a distinctive shape, even when it is not immediately obvious, as in the armless species Culcita novaeguineae (Boyer and Bearzi, 2003). Once these are looked at from the ventral side, the pentaradial structure is obvious. Brittle stars have long, thin, flexible arms, and a small round or pentagonal central disc, e.g. the class Ophiuroidea. The number of arms can vary from five in a species such as the northern star Asterias rubens, to as many as 50 in the Labidiaster annulatus (Shine, 2002). The sunstar, Solaster endeca, has long, thin arms, while the cushion sea star, Oreaster reticulatus, has short, wide arms. Sea stars range in size from the blood sea star (Henricia sanguinolenta), which is as small as the thumb, to the Northeastern P
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2 hours, and these planktonic larvae have bilateral symmetry. They go through several stages of development in the first three to four weeks, and then settle to the bottom and attach themselves to rocks, seaweed, or other solid objects, where they quickly undergo metamorphosis and become sea stars. Few of the larvae survive to maturity, but those that do reach sexual maturity within one year (Shine, 2002). Some large sea stars in the Antarctic, which move very slowly because of the cold water, have been studied for many years, and although exact life spans are unknown, it is believed they may live as many as 50 to 100 years.
In species that live in harsh environments, such as deep or extremely cold water, the adults hold their young in their stomachs or against their bodies until they have developed to give them a chance at survival (Shine, 2002). The young of these species do not go through the planktonic stage. Several species reproduce asexually as well as sexually, and one species, Stephanaserias albula, does not produce eggs or sperm, and reproduces solely by division and regeneration. Prior to division, the skin is rearranged so that after division, it can cover the open wounds to prevent infection. After this is
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Approximate Word count = 1687
Approximate Pages = 7 (250 words per page)
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