brittlestar


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brittlestar,

common name for echinoderms belonging to the class Ophiuroidea. The name is derived from their habit of breaking off arms as a means of defense. New arms are easily regenerated. They are also called serpent stars because of the snakelike movements of the five mobile, slender arms.

Brittlestars can be distinguished from sea starssea star,
also called starfish, echinoderm of the class Asteroidae, common in tide pools. Sea stars vary in size from under 1-2 in. (1.3 cm) to over 3 ft (90 cm) in diameter. They are commonly dull shades of yellow or orange, but there are many brightly colored ones as well.
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, or starfish, by their rounded central disk, sharply set off from the arms. They have the water-vascular system and tube feet common to all echinoderms; unlike sea stars, brittlestars lack open grooves (ambulacral grooves) on the lower surface of the arms, and the tube feet serve as tactile organs. Also unlike sea stars, brittlestars walk with their arms; only some species use the tube feet for locomotion. Each arm contains a series of jointed, bonelike internal calcite plates, or ossicles, which determine the freedom of arm movements. The body and arms of brittlestars are also protected by calcite plates, which in some species consist of arrays of microlenses that focus light onto a nerve bundle, acting like a compound eye. Brittlestars can move quickly and in any direction.

Individuals are relatively small, usually less than 1 in. (2.5 cm) across the central disk, although the arms may be quite long. They are inconspicuous and often nocturnal, living under rocks, among seaweed, or buried in the sand. All are marine species, feeding on detritus and small living or dead animals. The arms move the larger food masses to the mouth, where they are fragmented by a complex jaw apparatus. Tube feet move smaller particles to the mouth. As a rule, sexes are separate, and fertilization occurs in the open sea after gametes have been discharged. A characteristic armed larval stage, the ophiopluteus, undergoes a profound metamorphosis to produce the rayed adult form.

About 2,000 species of ophiuroids are known, and a number are common along American coasts. Brittlestars are classified in the phylum EchinodermataEchinodermata
[Gr.,=spiny skin], phylum of exclusively marine bottom-dwelling invertebrates having external skeletons of calcareous plates just beneath the skin. The plates may be solidly fused together, as in sea urchins, loosely articulated to facilitate movement, as in sea
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, class Ophiuroidea.

References in periodicals archive ?
The view for the brittlestar, suspects Aizenberg, is "something like .
Juxtaligamental cells in the arm of the brittlestar Amphipholis kochii Lutken, 1872 (Echinodermata: Ophiuroidea).
Although the brittlestar seems to have crystal-clear vision--it flees predators and scouts out places to hide--scientists assumed its arms were the reason.
The calcite microlenses expertly compensate for birefringence and spherical aberration - physical effects common in lenses that distort light - and scientists hope to mimic nature's success and design microlenses based on the brittlestar model.
Organisms may have to either devote additional energy toward calcification at the expense of other processes, such as reduced muscle mass in adult brittlestars (Wood et al.
These processes were similar to those of the juxtaligamental cells of brittlestars (Wilkie, 1979).
Previously, we presented a brief description of stomach lining regeneration after central disk autotomy in the brittlestar Amphipholis kochii (Frolova and Dolmatov, 2006).
Measures of tissue loss and regeneration by the brittlestar Microphiopholis gracillima (Echinodermata: Ophiuroidea).
Mass spawning by two brittlestar species Ophioderma rubicundrum and O.
Localization of catecholamines in the nervous system of a starfish, Asterias rubens and of a brittlestar, Ophiothrix fragilis.
0%) were comparable to COI and control region genetic distances among congeneric species in other sea star and brittlestar phylogenetic analyses (e.
The species-rich brittlestar genus Macrophiothrix is common in certain Australian coral reef communities.