Ophiuroidea

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Related to ophiuroid: class Ophiuroidea, Brittle stars

Ophiuroidea

[äf·ə·yə′rȯid·ē·ə]
(invertebrate zoology)
The brittle stars, a subclass of the Asterozoa in which the arms are usually clearly demarcated from the central disk and perform whiplike locomotor movements.

Ophiuroidea

 

(brittle stars), a class of benthic marine animals of the phylum Echinodermata. The body consists of a flat disk, which usually measures about 2 cm across (sometimes up to 10 cm). Five or, less frequently, ten flexible arms extend from the disk. The length of each arm is several times (sometimes 20 to 30 times) greater than that of the disk. In contrast to the arms of starfishes, the arms of brittle stars are sharply marked off from the disk and are jointed, consisting of numerous vertebrae. Most brittle stars have simple, unbranched arms. The disk and the arms are covered with thin calcareous plates.

In most species the sexes are separate. Development is usually by metamorphosis; the free-swimming larva is called an ophiopluteus. Some species are viviparous; others are capable of reproducing by division.

Brittle stars crawl by flexing their arms, or they bury themselves in the bottom. They feed on small animals or detritus. Many tropical species that inhabit shallows are brightly colored. Some species are capable of luminescence. The regeneration of arms is well developed.

Brittle stars are found throughout the world on ocean and sea bottoms (to depths of 8 km). They often form large colonies and serve as food for fishes. Some species live commensally with algae, sponges, corals, and sea urchins. Of the approximately 2,000 species, about 120 are encountered in the seas of the USSR. Fossils of extinct species have been traced to the Ordovician.

G. M. BELIAEV

References in periodicals archive ?
The digestive epithelium of the ophiuroid stomach includes four cell types: enterocytes, two types of granular cells, and mucocytes (Jangoux, 1982; Byrne, 1994).
Significant intraspecific variation in SCB abundance has been observed in ophiuroids (Foret and Lawrence, 2001), and there is no apparent reason why it should not also occur in the echinoderms studied here.
The stations where interrupted fishing effort was identified presented a higher biomass of sessile, like sponges or ascidians, and fragile organisms, like little ophiuroids, than the sites continuously disturbed up to 2007.
2] was the same between the two studies, our biomass was higher because NCC had ophiuroids throughout the sampling period, adding about 4 g [m.
2]), places dominated by subsurface deposit-feeders, such as the amphipod Microphoxus cornutus, and the ophiuroids Amphipholis subtilis, A.
Disturbances may also accelerate the production of asexual propagules, particularly in organisms that reproduce by fragmentation such as sponges (Wulff 1985), gorgonians (Lasker 1990), corals (Tunnicliffe 1981; Highsmith 1982), asteroids (Crump and Barker 1985), and ophiuroids (Mladenov and Emson 1990).
The rest of megafauna were constituted by six species of crustaceans Heterocarpus reedi (n = 330), Projasus bahamondei (n = 130), Munida propinqua (n = 8), Uroptychus parvulus (abundance no recorded), Chirostylus hendersoni (n = 32) and the stomatopod Pterygosquilla armata (n = 47), two species of ophiuroids (Gorgonocephalus chilensis and Astrotoma agassizi; n = 14 and 102, respectively), an unknown species of asteroid (n = 1) and one species of Anthozoa Hormathia cf.
In the southern sector, a general lower abundance of scallops and predators, together with higher density of ophiuroids, in comparison with the other sector.
Carter and Steele (1982b), using their own results and data from nonconcomitant studies conducted at different sites in Newfoundland (Squires, 1970; Ennis, 1973), have suggested that lobsters of 12-73 mm CL consume sea urchins, ophiuroids, and mussels more frequently than larger (adult) lobsters.
Approximately 7000 known species are organized in five classes, including crinoids (sea lilies and feather stars), asteroids (starfishes), ophiuroids (brittlestars), echinoids (sea urchins and sand dollars).
In individual analyses of 16S rDNA alone (not shown), Rhabdopleura sequences were recovered within the echinoderm outgroup as sister to ophiuroids.