Common brittlestar (Ophiothrix fragilis)
|Size||Central disc diameter: up to 20 mm (2)|
Common and widespread.
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).
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).
Occurs from the lower shore to depths of around 150m (3), living on hard substrates (2).
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).
Not currently threatened.
Conservation action has not been targeted at this common species.
For more on this species see the Marine Life Information Network (MarLIN) species account:
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- Cryptic colouration: colouration that makes animals difficult to detect against their background. The colouration may provide camouflage against a background or break up the outline of the body. Both can occur in a single animal, and tend to reduce predation.
- Larvae: stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Metamorphose: an abrupt physical change from the larval to the adult form.
- Planktonic: aquatic organisms that drift with water movements; may be either phytoplankton (plants), or zooplankton (animals).
National Biodiversity Network Species Dictionary (November, 2002)
Jackson, A. (1999) Ophiothrix fragilis. Common brittle star. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. (November, 2002)
- Fish, J.D. and Fish, S. (1996) A student's guide to the seashore. Second Edition. Cambridge University Press, Cambridge.
Ulster Museum: Marine Life. (November, 2002)