The Ophiurida are an order of

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea ...

s within the

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

Ophiuroidea Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...

. It includes the vast majority of living brittle stars.

Characteristics

Ophiurida have

bursa ( grc-gre, Προῦσα, Proûsa, Latin: Prusa, ota, بورسه, Arabic:بورصة) is a city in northwestern Turkey and the administrative center of Bursa Province. The fourth-most populous city in Turkey and second-most populous in the ...

e for respiration and excretion, and dorsal and ventral arm shields are present and usually well developed. Arms are unbranched and incapable of coiling vertically. Most are five-armed, some with 4 or 6 arms as an abnormality, but others properly bear six or seven arms. The

madreporite The madreporite is a light colored calcareous opening used to filter water into the water vascular system of echinoderms. It acts like a pressure-equalizing valve. It is visible as a small red or yellow button-like structure, looking like a smal ...

is on the oral surface. The digestive glands are entirely within the central disc. They move their arms side to side by means of

ball-and-socket joint The ball-and-socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of ...

s. Tropical species tend to contrast color from the environment, but most others prefer to blend in. These biochromes do not include echinochromes.

Systematics and phylogeny

There is currently no consensus as to the subdivision of the Ophiurida. The order has been divided into the following suborders and infraorders * Ophiomyxina *

Ophiurina Ophiurina are a suborder of brittle stars containing the majority of living brittle star species. Systematics There is currently no consensus as to the subdivision of the Ophiurina (traditionally, the infraorders have been treated as suborders). ...

** Hemieuryalina ** Chilophiurina **

Gnathophiurina The Gnathophiurina are a group of Ophiuroidea mostly treated as suborder (but at first as an order Gnathophiurida, and sometimes as infraorder of OphiurinaSmith, A.B.; Paterson, G.L.J. . Ophiuroid phylogeny and higher taxonomy: morphological, mo ...

** Ophiodermatina ** Ophiolepidina Another classification scheme divides it into the following suborders: * Chilophiurina Matsumoto, 1915 * Laemophiurina Matsumoto, 1915 *

Ophiothricidae Ophiotrichidae are a family of ophiurid brittle stars within the suborder Gnathophiurina. All have arms with delicate translucent, thorny spines. The arms are flexible in all directions. The jaws contain clusters of well-developed tooth papillae ...

Ljungman, 1867 (= Ophiotrichidae) *

Müller & Troschel, 1840 Another classification scheme divides it as: * Chilophiurina * Laemophiurina *

Ecology

Ophiurida have a world-wide distribution range and are found in oceans in different depths. Most of them are

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

s or

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

feeders.

References

Ophiuroidea Extant Devonian first appearances {{Ophiuroidea-stub