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Examples the Echinoderms. Friend may have seen sea stars and sand dollars in ~ the beach due to the fact that they live in shallow water close to the shore. Other echinoderms, such as feather stars, space less typically seen because they live in the deep ocean.

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Structure and role of Echinoderms

Echinoderms are called for their “spiny skin.” However, the spines aren’t on their skin. Castle are part of the endoskeleton. The endoskeleton consists of calcium carbonate plates and spines, spanned by a slim layer of skin. Adult echinoderms have radial symmetry. This is simple to view in the sea star and also sand dissension in Figure above. However, echinoderms evolved from an ancestor v bilateral symmetry. Proof for this is the bilateral the contrary of their larvae.

A distinct feature the echinoderms is their water vascular system. This is a network of canals that extend along each body part. In many echinoderms, the canals have outside projections called tube feet (see Figure below). The feet have suckers on the ends. Muscle contractions pressure water right into the feet, causing them to expand outward. Together the feet extend, they affix their suckers to brand-new locations, farther away from your previous clues of attachment. This outcomes in a slow but powerful form of movement. The suckers are very strong. Castle can also be supplied to pry open the shells the prey.


Tube Feet the a Sea Star. The pipe feet the a sea star (in white) are part of its water vascular system. Over there is a sucker ~ above the end of each foot that permits the pet to “walk” slowly over a surface. The suckers are strong enough to pry open shells.

Echinoderms absence respiratory and also excretory systems. Instead, the thin walls of their tube feet allow oxygen come diffuse in and also wastes to diffuse out. Echinoderms likewise lack a central nervous system. They have actually an open circulatory system and lack a heart. Top top the various other hand, echinoderms have actually a well-developed coelom and a complete digestive system. Echinoderms use pheromones to interact with every other. They detect the chemicals through sensory cell on your body surface. Some echinoderms likewise have basic eyes (ocelli) that can sense light. Like annelids, echinoderms have actually the capability to regenerate a absent body part.

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Echinoderm Classification

Living echinoderms are placed in 5 classes. These five classes show numerous similarities. Biology in each class are explained in Table below.

class (includes) description Example


feathers stars sea lilies
fewer than 100 species; countless have more than five arms; earliest and also most primitive echinoderms; live ~ above the ocean floor, greatly in deep water; filter feeders

feather star



sea stars
almost 2000 species; many have five arms; countless are brightly colored; live on the s floor, largely in shallow water; predators or scavengers

sea star



brittle stars
about 2000 species; main disk unique from arms; relocate by flapping their arms, which lack suckers; live top top the ocean floor in shallow or deep water; predators, scavengers, deposit feeders, or filter feeders

brittle star