Ophiuroidea

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Related to ophiuroids: class Ophiuroidea, Brittle stars, echinoids

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 ?
In winter the highest value was due to the presence of the polychaete Spirographis spallanzani (with approximately 50 g each individual) and numerous and/or large ophiuroids as Hemipholis elongata, Amphiodia atra and Ophioderma januarii.
Otherwide, it might be expected that they would be associated with areas rich in benthic food, such as ophiuroids, which are known to form part of the diet of other gobies (Gibson, 1982).
Juxtaligamental system of the disc and oral frame of the ophiuroid Amphipholis kochii (Echinodermata: Ophiuroidea) and its role in autotomy.
It includes a detailed description of the ultrastructure of the intact digestive system, since the only other published ultrastructural accounts of the intact ophiuroid digestive system have been based on species from a single family--the Ophiodermatidae (Schechter and Lucero, 1968; Deschuyteneer and Jangoux, 1978; Byrne, 1994)--the feeding biology of which is probably very different from that of the Amphiuridae.
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.
Ophiuroids also possess bilaterally symmetrical feeding larvae, called ophioplutei, with anteriorly directed arms, and they resemble echinoplutei.
In contrast, vast variation in mode of development among many families or genera of gastropods, polychaetes (Kupriyanova, 2003; Pernet, 2003), and ophiuroids, and phylogenetic analyses of such groups show that transitions in mode of development have occurred frequently and recently (e.
schayeri contain just enough energy to support development without feeding, or do ophiuroids use their lipids at a much lower rate, thereby leaving deposits for the early juvenile stage?
Among echinoderms, specificity of sperm chemotaxis has been found mainly at the family level in holothurians and at the genus or species levels in ophiuroids (Miller, 1997).
Ophiuroids (brittlestars) are of special interest because they produce a feeding pluteus larva that is similar in structure and function to the echinoid pluteus.
In echinoderms, intragonadal incubation of embryos is known for one crinoid, four ophiuroids, four holothuroids, and five asteroids (Table 1).