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Star fish also called sea star, any marine invertebrate of the classasteroidean (phylum echinodermata) having rays or arms,surrounding an indistinct disk. They are not fishes.

The 1800 living species of starfishes occur in all oceans; the

northern pacific has the greatest variety. Most species are 20 to 30cm ( 8 to 10 inches) across; some are only 1 cm (0.4 inch), andothers are as much as 65 cm (25 inches) across.

Starfish arms typically five in number- are hollow and, like thedisk, covered with short spines and pedicellariae (pincerlike organs);on the lower side are grooves with rows of tube feet, which may besucker tipped. A starfish can lose one or more arms and grow newones. Its tube feet let it creep in any direction or cling to steepsurfaces.

Primitive starfishes feed by sweeping organic particles along thearm of the grooves into the mouth on the underside of the disk.Advance forms either evert (turn outward) the stomach upon theprey (bivalve, mollusk, coral polypsm other echinoderms) forexternal digestion or swallow the prey whole. The internal skeletonof the starfish consists of limy plates. Respiration usually is throughskin structures. Light sensitive spots occur at the tips of the arms.

Starfish reproduction typically is heterosexual, but hermaphroditism(reproductive organs of both sexes in one animal) occurs, and a few

sea stars reproduce sexually by division of the body (fission). Somebrood their eggs and young; nonbrooders may release into thewater as many as 2.5 million eggs at a time .

Starfishes with long stalked, two valved pedicellariae with longstalked, two valved pedicellariae comprise the order forcipulata-the forceps carrier. The pedicellariae have protective and,sometimes, food taking functions. In most species the arms are longand rounded, and the disk is small

Starfish. Encyclopaedia Britannica. Retrieved September 24, 2010,from Encyclopaedia Britannica 2006 Ultimate Reference Suite DVD.

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Brittle Star also called serpent star any of the 2000 living species of

marine invertebrates comprising the class Ophiuroidea (phylumEchinodermata). Their long, thin arms0 usually five and often forkedand spiny- are distinctly set off form the disk- shaped body. Thearms readily break off but soon regrow or regenerated.

The mouth, on the others side of the body , has five teeth; an anusis lacking; and the tube feet serve mainly as sense organs fordetecting light and odour. the animals feeds by extending one ormore arms into the water or over the mud, the other arms servingas anchors. Brittle stars, although mainly scavengers and planktonsfeeders, sometimes trap sizable animals. They are capable ofmoving jerkily but usually cling to the seafloor or to sponges orcnidarians.

Brittle stars occupy many marine habitats, often at great depths.The most widespread species is the long-armed brittle star(Amphipholis squamata ), a grayish or bluish species that is stronglyluminescent. Two of the best know littoral species are the greenbrittle star (Ophioderma brevispina), found for Massachusetts tobrazil, and the common European brittle star (Ophiothrix fragilis).

Brittle stars with many-branched, much-coiled arms are calledbasket stars. Most live in deep waters.

Brittle star. Encyclopaedia Brittanica. Retrieved September 24,2010, form Encyclopaedia Brittanica 2006 Ultimate Reference SuiteDVD

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Sea urchins

Any of the about 700 living species of echinoid marine invertebrates(phylum Echinodermata) with a globular body and a radialarrangement of organs, shown by five bands of pores running frommouth to anus over the test (internal skeleton). The poresaccommodate tube feet, which are slender, extensible, and oftensucker tipped. From nodules on the test arise long , movable spinesand pedicellariae (pincerlike organs); these structures may havepoison glands. The mouth on the underside of the body has acomplex dental apparatus called Aristotles lantern, which also maybe venomous. Teeth are extruded to scrape algae and other foodfrom the rocks, and some urchins can excavate hiding places incoral or rock- even in steel. Sea urchins live on the ocean floor,usually on hard surfacesm and use the tube feet or spines to moveabout.

The largest urchin (known from a single specimen) is Sperostomagiganteum of deep waters off japan. Hatpin urchins, such as

Centrostephanus longispinus of the Mediterranean and easternatlantic, Diadema (formerly Centrechinus) setosum of the indopacific, and D.antillarum of florida and west inies, have a toxic spineup to 30 centimeters (12 inches long). The slate pencil urchin(Heterocentrotus mammillatus) of the indo pacific has 12-cm spinesthat may be 1 cm thick stout enough to be used for writing.

Sea urchin. Encyclopaedia Brittanica. Retrieved September 24,2010, from Encyclopaedia Brittanica 2006 Ultimate Reference SuiteDVD.

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Sea cucumber any of the 1100 of species of marine invertebratesconstituting the class Holothuroidea of the Phylum Echinodermata.The soft, cylindrical body, 2 to 200 cm ( about inch to 6 feet)long and 1 to 20 cm (0.4- 8 inches) thick usually is a dull, darkcolour and often warty, thus resembling a cucumber, the internalskeleton is reduced to numerous distinctively shapedm tiny bits inthe skin. The most species have five rows of tube feet extendingform mouth to anus. The anal opening is used for both respirationand discharging of wastes. The 10 or more retractile tentaclessurrounding the mouth are used for food taking (mud containingnutrients or small aquatic animals) or burrowing. LocomotionIs sluglike

Many sea cucumber can expel their internal organs form the anus

and grow new ones; this may be a device for escape from apredator, or it may occur for physiological reasons. Some speciesalso expel sticky filaments that ensnare or confuse an enemy.Cucumbers shelter pearfish (Carapus species) in the anal cavitymwith the head of the fish extruding. A number of sea cucumbersexude a toxin that is lethal to small animals but not to humans;south sea islanders place sea cucumbers juices in water to killstupefy fish. For the use of sea cucumbers as food.

Sea cucumbers are found in all oceans, mostly shallow water butsometimes at great depths. They are best represented in the Indian

ocean and the western pacific, the 80-100 species of large, wartycucumbers of the genus Holothuria are abundant of coral reefs.

Sea cucumber. Encyclopaedia Britannica. Retrieved September 24,2010, from Encyclopaedia Britannica 2006 Ultimate 2006 ReferenceSuite DVD.