The ophiuroids generally have five long, slender, whip-like arms which may reach up to 60 cm (24 in) in length on the largest specimens.

[3] However, brittle stars are also common members of reef communities, where they hide under rocks and even within other living organisms.

However, they have several types of sensitive nerve endings in their epidermis, and are able to sense chemicals in the water, touch, and even the presence or absence of light.

Digestion occurs within 10 pouches or infolds of the stomach, which are essentially ceca, but unlike in sea stars, almost never extend into the arms.

Basket stars in particular may be capable of suspension feeding, using the mucus coating on their arms to trap plankton and bacteria.

In large, crowded areas, brittle stars eat suspended matter from prevailing seafloor currents.

Ophiura Linnaeus hunts epibenthic animals and the Antarctic Ophiosparte gigas is an active predator.

Gas exchange and excretion occur through cilia-lined sacs called bursae; each opens between the arm bases on the underside of the disk.

[5] Both the Ophiurida and Euryalida (the basket stars) have five long, slender, flexible, whip-like arms, up to 60 cm in length.

The ossicles are surrounded by a relatively thin ring of soft tissue, and then by four series of jointed plates, one each on the upper, lower, and lateral surfaces of the arm.

The two lateral plates often have a number of elongated spines projecting outwards; these help to provide traction against the substrate while the animal is moving.

The spines, in ophiuroids, compose a rigid border to the arm edges, whereas in euryalids they are transformed into downward-facing clubs or hooklets.

In the Paleozoic era, brittle stars had open ambulacral grooves, but in modern forms, these are turned inward.

One arm presses ahead, whereas the other four act as two pairs of opposite levers, thrusting the body in a series of rapid jerks.

Although adults do not use their tube feet for locomotion, very young stages use them as stilts and even serve as an adhesive structure.

Many species brood developing larvae in the bursae, effectively giving birth to live young.

[5] Some brittle stars, such as the six-armed members of the family Ophiactidae, exhibit fissiparity (division through fission), with the disk splitting in half.

The West Indian brittle star, Ophiocomella ophiactoides, frequently undergoes asexual reproduction by fission of the disk with subsequent regeneration of the arms.

A study of the age range of the population indicates little recruitment and fission is the primary means of reproduction in this species.

The time period between successive divisions is 89 days, so theoretically, each brittle star can produce 15 new individuals during the course of a year.

Ophiuroids use this ability to escape predators, in a way similar to lizards which deliberately shed the distal part of their tails to confuse pursuers.

Brittle stars move fairly rapidly by wriggling their arms which are highly flexible and enable the animals to make either snake-like or rowing movements.

Deep-water species tend to live in or on the sea floor or adhere to coral, urchins, or xenophyophores.

Around 270 genera are known, these are distributed in 16 families,[1] which makes them at the same time a relatively poorly diversified group structurally, compared with the other echinoderms.

[11] For example, 467 species belong to the sole family of Amphiuridae (frail brittle stars which live buried in the sediment leaving only their arms in the stream to capture the plankton).

[11] List of families according to the World Register of Marine Species, following O'Hara 2017: The first known brittle stars date from Early Ordovician.

[13] Silurian fossils from a minor mass extinction called the Mulde event shows the ancestors of modern brittle stars went though a bottleneck, where a miniaturization caused by paedomorphosis led to structural simplification of their skeletal anatomy.

Larger brittle stars are popular because, unlike Asteroidea, they are not generally seen as a threat to coral, and are also faster-moving and more active than their more archetypical cousins.