sea urchin, spherical-shaped echinoderm with movable spines covering the body. The body wall is a firm, globose shell, or test, made of fused skeletal plates and marked by regularly arranged tubercles to which the movable spines are attached. Five rows of the skeletal plates are pierced by pores for the tube feet of the water-vascular system; these are typical of echinoderms and are used for locomotion. The mouth is centered on the lower side of the body and in many species is surrounded by a whorl of gills. A complex jaw and tooth apparatus in the mouth, known as Aristotle's lantern, is used to fragment food. Long, sharp spines are used for protection, and in some species are poisonous. The spines are also used as levers, aiding the tube feet in locomotion and, along with the teeth, are used by some species to dig burrows in hard rock. Sea urchins feed on all kinds of plant and animal material; some eat sand or mud, digesting out organic material that is present. Entirely marine, they occur in all seas and at all depths but prefer shallower waters and rocky bottoms. Arbacia and Strongylocentrotus are the most familiar American genera; one species of the latter, the red sea urchin (S. franciscanus) of the Pacific coast, is estimated to live for 200 years or more. Eggs and sperm are shed into the sea. After fertilization, a characteristic, free-swimming larva, called the pluteus larva, develops; it undergoes a profound metamorphosis to assume the adult form. Sea urchins have some economic significance. The roe is considered a delicacy, especially in Mediterranean regions and Japan, and burrowing species may damage sea walls. Sea urchins also are used in embryological studies. Sea urchins are classified in the phylum Echinodermata Echinodermata (əkī'nōdûr`mətə) [Gr.
..... Click the link for more information. , class Echinoidea, subclass Regularia.
Any of about 700 species (class Echinoidea) of echinoderms found worldwide. Sea urchins have a globular body covered with movable, sometimes poisonous, spines up to 12 in. (30 cm) long. Pores along the internal skeleton accommodate slender, extensible, often sucker-tipped tube feet. Sea urchins live on the seafloor and use their tube feet or spines to move about. The mouth is on the body's underside; teeth are extruded to scrape algae and other food from rocks. Some species excavate hiding places in coral, rock, or even steel. Roe of some species is eaten in certain countries.
sea urchin
..... Click the link for more information. , class Echinoidea, subclass Regularia.
sea urchin
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Slate-pencil urchin (Heterocentrotus mammillatus)
(credit: Douglas Faulkner)
sea urchin
any echinoderm of the class Echinoidea, such as Echinus esculentus (edible sea urchin), typically having a globular body enclosed in a rigid spiny test and occurring in shallow marine waters
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