An+Overview+of+Echinoderms

= ** Echinoderms are a highly diversified animal phylum. Due to their large fossil record, unusual characteristics, and significant ecological role in the marine ecosystem, they have long allured scientists. They are found at every ocean zone and depth, occupying a variety of habitats. The first definite member of the phylum, emerged in the Cambrian period. Today, there are 7,000 exiting species, declaring it the largest phylum with marine representatives. ** =

** Distribution/Habitat ** -Distributed globally in all depths of the ocean. -Reach their highest diversity in coral reef environments, but are also common on shallow shores, and in deep waters. -Are benthic, meaning that they live on the sea floor. -Many species can live throughout the ocean, and through the exploitation of ocean currents, can swim great distances.

-The evolutionary ancestors of Echionoderms were animals with bilateral symmetry. This characteristic is further seen in echinoderm larvae, who organize in a bilaterally symmetric style. Later, the right side of the body is absorbed by a growing left side. This remaining left side develops pentaradially (body contains five parts and a central axis.) -Have a unique water vascular system, which is a web of canals that operate in gas exchange, feeding, and locomotion. The main component are the tube feet, which function through fluid pressure to pass food through the mouth at the center, and can attach to surfaces. -Digestive system often leads directly from the mouth to the anus. Circulatory system consists of five important vessels, and there is considered to be "no true heart." There is a lack of a specialized execratory system, therefore nitrogenous waste often diffuses as ammonia through the tube feet. There is a simple nervous system, with interconnected neurons and no central brain. -Many have the power of regeneration (process of renewal, restoration, growth.)
 * Structural Characteristics **

** Reproduction ** -Echinoderms reach sexual maturity after two to three years of life. Eggs and sperm are released into open waters, allowing fertilization to take place. Habitual isolation, and temporal isolation, serve as reproductive isolating mechanisms.

** Predation ** -Echinoderms posses a low nutrition value, and indigestible calcite. -Many organisms (crabs, shares, sea birds) prey on them. -Defensive strategies includes toxins, deceived through the tube feet.

** Ecological Role ** -Provide a key ecological role in ecosystems. -Some, contribute to the depletion of the sea floor's nutrients. This allows for the sea floor to by more further penetrated, increasing the depth to which oxygenation occurs. -Are the staple diet of many organisms, especially the otter. -Form symbiotic relationships, for example, the sea cucumber provides a habitat for parasites. -The extinction of a large population of echinoderms, can cause the destruction of an entire reef.

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**Sources** [] [|http://library.thinkquest.org/26153/marine/enchino.htm] [|http://www.pbs.org/kcet/shapeoflife/animals/echinoderms.html] [|http://kentsimmons.uwinnipeg.ca/16cm05/1116/33-37-EchinodermsCollage.jpg] [|http://www.learningcommunity202.org/PEHS/departments/science/tmurphy/animals_fourth/Echinoderms/Assets/echinoderm_variety__oban.jpg] [|http://biology.unm.edu/ccouncil/Biology_203/Images/Deuterostomes/adultseastardiagram.gif] [|http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Echinodermata/Class%20Asteroidea/Solaster_dawsoniOssiclesMarginal1sDLC2005.jpg] []