Common Brittlestar

Common brittle stars are prey to many species of fish, portunid crabs, and some species of starfish. Their main predators include ballan wrasses, cuckoo wrasses, common dragonets, velvet crabs, spiny starfish and common starfish. Brittle stars have two main defense mechanisms against predators such as these. They have cryptic coloring and behaviors, often feeding at night and hiding during the day, and also have the ability to lose their arms, which later regenerate, to distract predators.

Known Predators:

• Common starfish (Asterias rubens)
• Common dragonet (Callionymus lyra)
• Ballan wrasse (Labrus bergylta)
• Cuckoo wrasse (Labrus mixtus)
• Velvet crab crab (Liocarcinus puber)
• Spiny starfish (Marthasterias glacialis)

Anti-predator Adaptations: cryptic

Common brittle stars have cryptic coloration, helping them avoid predation. Individuals are usually red, white, or brown and some are also banded or spotted. Their central body discs range from 2-20 mm in diameter and their five legs are very long and slim (typically five times the diameter of the body in length) and are segmented, with tube feet and seven serrated spines per segment. The central body is covered in spines as well.

Range length: 2 to 20 mm.

Other Physical Features: ectothermic ; heterothermic ; radial symmetry

Sexual Dimorphism: sexes alike

This species lives an average of 10 years in the wild. Nothing is known about their lifespan in captivity.

Average lifespan
Status: wild: 10 years.

Common brittle stars are epifaunal and live in extremely large groups offshore (as many as 2000 individuals recorded) known as brittle star beds. Within the intertidal zone, they are most often found individually. They typically prefer hard substrata (sand and shell bottoms) and are often found under shells or rocks, but can be found on rocky reefs and soft substrata as well. This brittle star is found in shallow waters but also as deep as 350 m, and prefers areas with strong current. Because high levels of sedimentation can prevent them from feeding and eventually halt respiration, this species avoids areas of high sedimentation.

Range depth: 0 to 350 m.

Habitat Regions: temperate ; tropical ; saltwater or marine

Aquatic Biomes: benthic ; reef ; coastal

Common brittle stars are commonly found off the coast of the British Isles (though unrecorded from the east coast of Scotland) as well as on all other coasts bordering the North Sea and throughout the eastern Atlantic Ocean, as far south as the Cape of Good Hope. They are also found around the Azorean Islands.

Biogeographic Regions: palearctic (Native ); ethiopian (Native ); oceanic islands (Native ); atlantic ocean (Native )

This brittle star is a nocturnal passive suspension feeder. To feed, it lifts its arms through crevices in rocks, passing particles to its mouth where it uses the two pairs of tube feet in its mouth and both a vertical row of teeth and group of tooth papillae to consume its food. This species' diet is made up largely of detritus, diatoms, and phytoplankton. It will also occasionally scavenge dead material.

Animal Foods: carrion

Plant Foods: phytoplankton

Other Foods: detritus

Foraging Behavior: filter-feeding

Primary Diet: carnivore (Scavenger ); planktivore ; detritivore

Not much is known about how these brittle stars communicate. It is known that they form their beds based on interaction with other brittle stars, not due to environmental cues. They is some evidence that they communicate using pheromones (as do other echinoderms), particularly during breeding.

Communication Channels: tactile ; chemical

Other Communication Modes: pheromones

Perception Channels: tactile ; chemical

Common brittle stars have not been evaluated for the IUCN Redlist. However, due to their general abundance, the species is not considered to be in need of targeted conservation efforts.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

Common brittle stars have three major life stages: larva, juvenile, and adult. Development from the larval to the adult stage takes 20-30 days, depending on nutrient availability, while development to full maturity may take 6-10 months.

Common brittle star eggs are 0.1 mm in diameter. Approximately 12 hours after fertilization, the oval-shaped larvae leave their egg membranes and form a vacuolated crest (a crest with a fluid-filled cavity in the center). A day later they form posterolateral arms. The beginning of the exotrophic larval period is determined by the formation of the mouth and anus (typically during the third day). During the next 10 days, common brittle stars develop their anterolateral, postoral, and postdorsal pairs of arms. Metamorphosis begins around the 15th day of development, signaled by the split of the hydrocoele (water vascular system) into 5 lobes and subsequent wrapping around the esophagus. Next, brittle stars enter the endotrophic period. Their larval arms (not including the posterolaterals) regress, followed by the regression of the esophagus and intestine. During this time, larvae begin to develop their five adult tentacles as well as mouths and, on the undersides of the arms, tube feet (podia). Finally, juveniles lose their larval posterolateral arms and develop hooks on the ends of their arms which are used to latch on to adults. Juveniles depend on adults to help them feed until they are capable feeding on their own.

Development - Life Cycle: metamorphosis

Dense aggregations of these brittle stars can be a nuisance to fisherman.

Common brittle stars have no known economic importance to humans.

Common brittle stars have several ecological roles. This species is prey for a variety of fish, crabs, and starfish and their large beds can create shelter for other animals such as bivalves. These animals feed upon diatoms and phytoplankton, removing particulates from the water column; they are also detritivores, feeding on decaying material from the ocean floor. Common brittle stars are host to a number of ectoparasitic copepod species, and some studies have found that they have become a host to an orthonectid species as well.

Ecosystem Impact: biodegradation

Commensal/Parasitic Species:

• Collocheres gracilicauda (Subclass Copepoda, Subphylum Crustacea)
• Paranthessius anemoniae (Subclass Copepoda, Subphylum Crustacea)
• Thalestris longimana (Subclass Copepoda, Subphylum Crustacea)
• Thaumatopsyllus paradoxus (Subclass Copepoda, Subphylum Crustacea)
• Rhopalura ophiocomae (Family Rhopaluridae, Class Orthonectida)

Common brittle stars mate by releasing sperm and eggs into the water, with the release of sperm by the males triggering females to release eggs. The eggs are fertilized and develop in the water column. Although Common brittle stars have been reported to breed year-round in some areas, and as late as October in others, gonads are typically most developed from May-July.

Mating System: polygynandrous (promiscuous)

It is believed that individuals reach sexual maturity at approximately 10 mm body disc diameter, though gonad tissue can be found in individuals as small as 3 mm. This species typically breeds during the summer months from May-July, but there is evidence that some of the population may be able to breed throughout the year. Individuals usually spawn once per breeding season.

Breeding interval: Common brittle stars generally spawn once per year

Breeding season: May to July

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; induced ovulation ; fertilization (External ); broadcast (group) spawning

Adult common brittle stars help juveniles to feed. The juveniles they aid, however, may not be their own: as larvae develop in the water column, strong currents may cause a passive migration, taking them to an entirely different population.

The common brittlestar forms dense aggregations offshore, with as many as 2000 individuals recorded per square meter (2). When it occurs in the intertidal zone, it is more typically found as single individuals in crevices, under stones and amongst seaweed (4). It feeds by raising the arms above the substrate, and extending the tube-feet, which remove particles from the water (3). It then passes food along the arms to the mouth (3). It is also known to scavenge on decaying matter (3). Many species predate on this brittlestar. It tends to avoid predation by moving away from any disturbance (2). Cryptic colouration and a tendency to hide in crevices may also help it to reduce the risk of predation (2). Study of bands in the skeletons of this species has suggested that it may be fairly long-lived, with the largest specimens estimated to be around 10 years old (2). The breeding season is thought to extend from May to January, although most reproductive activity seems to occur in summer and autumn (2). Each individual is believed to spawn just once each breeding season (2). A week after spawning, the planktonic larvae appear in the water column (2). They metamorphose into young brittlestars whilst drifting in the plankton, before settling after around 26 days (2).

Conservation action has not been targeted at this common species.

Like all brittlestars, the common brittlestar has five long, slender arms, which radiate out from a central disc. The mouth is located in the centre of the underside of the disc, and there is no anus (3). This brittlestar varies greatly in colour, and may be red, brown, white or banded. The arms are covered in serrated spines (3), and are very fragile (2). The disc also bears spines and is roughly pentagonal in shape (4).

Occurs from the lower shore to depths of around 150m (3), living on hard substrates (2).

Found around the coastline of Britain, but is absent from the east coast of Scotland, the Humber Estuary, northern East Anglia and the southern part of the Kent coast (2). Elsewhere it has a wide range in the eastern Atlantic extending from northern Norway to the Cape of Good Hope, South Africa (2).

Common and widespread.

Not currently threatened.

The common brittle star lives up to its name: it is very brittle. Particularly the arms are very breakable, but fortunately should one fall off, they regenerate just like other starfish. Brittle stars have a relatively small body and long arms. They can have all kinds of beautiful colors. Using their roughly spined arms, they filter plankton out of the seawater. Common brittle stars are very sensitive to cold winters; their numbers can decrease strongly after a severe winter.

Ophiothrix fragilis is a species of brittle star in the order Ophiurida. It is found around the coasts of western Europe and is known in Britain as the common brittle star. It is also found along the coast of South Africa where it is known as the hairy brittle star.

Ophiopluteus larva. Spring - Summer

Low intertidal to 150 m depth, under stones on the shore and often in dense aggregations offshore (see Warner, 1971 and Broom, 1975 for descriptions of behaviour) on rough and gravelly ground; common all round the British Isles in places with strong currents