These mainly serve as camouflage or warning coloration displayed by many other marine animals as means of protection against predation. Patterns including mosaic-like tiles formed by ossicles, stripes, interconnecting net between spines, pustules with bright colors, mottles or spots. The aboral surface is also covered with papulae that are involved with the sea star's respiratory system.Ĭolor: Sea stars are often brightly colored, usually from reddish hues to violet, and unusual colors such as green and blue exist in some species, but come in muted colors as well. The radial canal which is across each arm of the sea star has tooth-like structures called ampullae, which surround the radial canal. There are large numbers of these pedicellariae on the external body which serve to prevent encrusting organisms from colonising the sea star. Pedicellariae: On the surface of the sea star, surrounding the spines, are small white objects known as pedicellariae. The eye is able to "see" only differences of light and dark, which is useful in detecting movement. Ranging from nearly pentagonal (example: Indo-pacific Cushion Star, Culcita novaeguineae) to gracile stars like those on Zoroaster genus.Įye: Sea stars have a simple eye at the end of each arm. Sea stars, while having their own basic body plan, radiate diversely in shapes and colors and the morphology differs between each species for example, a species of sea star may have rows of spines on their arms as means of protection. Additional parts like cribriform organs present exclusively in Porcellanasteridae are used to generate current in the burrows made by these infaunal sea stars. On the aboral surface there is a structure called the madreporite, which acts as a water filter and supplies the sea star's water vascular system with water to move. The spiny upper surface covering the species is called the aboral or dorsal surface. The mouth is located underneath the sea star on the oral or ventral surface, while the anus is located on the top of the animal. Most starfish have five arms, however some have more or less in fact some starfish can have different numbers of arms even within one species. As echinoderms need a delicate internal balance in their body, no sea stars are found in freshwater environments, with exception of very few species of sea stars found in slightly estuarine habitats.Įxternal anatomy: Sea stars are composed of a central disc from which arms sprout in radial symmetry. Habitat: Habitats could range from tropical coral reefs, kelp forests to deep-sea floor, although none of them live within the water column all species of sea stars found are living as benthos. Asterias is a common genus found in European waters and on the eastern coast of the United States Pisaster, along with Dermasterias ("leather star"), are usually found on the western coast. The greatest variety of sea stars is found in the northern Pacific Ocean. Name: As these creatures are echinoderms and not actually fish, most marine biologists prefer to replace the term starfish with the less misleading term sea star.ĭistribution: There are about 1,800 living species of sea star, and they occur in all of the Earth's oceans. The water vascular system has many projections called tube feet, located on the ventral face of the sea star's arms, which function in locomotion and aid with feeding. Skeleton: Sea stars do not have movable skeletons, but instead possess a hydraulic water vascular system. In fact, their evolutionary ancestors are believed to have had bilateral symmetry, and sea stars do exhibit some superficial remnant of this body structure. Starfish typically have five or more "arms" which radiate from an indistinct disk (pentaradial symmetry). They exhibit a superficially radial symmetry. The names sea star and starfish are also used for the closely related brittle stars, which make up the class Ophiuroidea. Sea stars or starfish are marine invertebrates belonging to Kingdom Animalia and phylum Echinodermata, class Asteroidea.
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