...Echinoderms are one of the most highly derived groups of animals with many species as significant components of several marine communities. They’re classified by three fundamental shared characteristics: 1) pentaradial symmetry, 2) skeleton made of three-dimensional calcitic elements, and 3) the presence of a water vascular system with an external opening. This water-vascular system (WVS), in particular, remains a unique application of a hydraulic system, generating pressure gradients that are able to command hundreds of tiny, adorable tube feet to crawl over uneven surfaces and feeding on tough shelled prey like mussels. The basic components of the WVS in non-crinoid echinoderms (below) include a circumoral ring canal with five radial canals extending from off of it. Also attached to the ring canal is the madreporite, which acts as a door between the external environment of the sea and the internal environment of the echinoderm. The madreporite, named after its resemblance to the Madreporaria coral (meaning “mother of the pores”), is lined with cells that beat tail-like flagella in a variety of directions.The fluid inside the WVS is similar to seawater in composition but contains up to 60% more potassium ions, slightly higher concentrations of chloride ions, and freely floating albuminous protein. Sea cucumbers have also been found to have red blood cells in their WVS. Each radial canal has serially repeating pairs of shorter canals that attach to the tube feet, which are operated...
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...or more, radiating out. They generally have mouths on their undersides. On their radiating segments they have tube feet with suction pads that help them to move along the ocean floor. Most have a slow motion, but the Pointed Sand star happens to be the fastest, and can move thirty inches in one minute. The class Asteroidea is characterized by a size of under two centimeters to twenty- four centimeters, with segements that extend from a central body. They have a water vascular system, which means that water runs through the canals on the radiating segments. When the canals of the segments are filled with water, they expand and help the sea star to move. Sea Stars have have a mesodermal, or inner skeleton made up of ossicles, or calcareous plates. The Pointed Sea Star has its own habitat, eating habits, and reproductive system. Like all marine life, it has an ecological importance and status. The habitat of the Pointed Sand Star is in salt water oceans, from tidal pools to depths of seven hundred feet on the east and southeast coastal areas. They can also be found along Central American and northern South American coastal regions. All sea stars, including the Painted Sand Star, are carnivorous. They eat many types of marine life, such as sponges or barnacles. To feed, they exert their stomach and digest their food, and when they are finished, move their stomachs inside themselves again. Sea stars do...
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