Ophiura albida
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Ophiura albida is a species of brittle star in the order Ophiurida. It is typically found on the seabed in the north eastern Atlantic Ocean and in the Mediterranean Sea and is sometimes known as the serpent's table brittle star.[2]
Description
Ophiura albida has a central disc reaching a diameter of about 1.5 centimetres (0.6 in) and five arms up to 6 centimetres (2.4 in) long. The disc is flattened and the upper surface is covered in small plates. These are mostly brick red but the plates at the edge of the disc close to where the arms are attached are white. The arms are slender and fragile, segmented and gradually tapering. The plates on the upper and lower sides have convex edges. Each segment has three short spines which lie flat on the surface and there are small pores between the plates. This latter fact helps to distinguish this species from the otherwise very similar Ophiura ophiura. The underside of the disc is a pale colour and has a central mouth with five large plates modified as jaws and fringed with teeth.[1][2][3]
Distribution and habitat
Ophiura albida is found at depths down to about 200 metres (660 ft), or 850 metres (2,790 ft) according to one authority. Its range extends from Norway to the Mediterranean Sea and the Azores. It occurs on the seabed on soft substrates including coarse sand, fine sand, gravel and muddy sand.[1][3] It is common round the coasts of the British Isles and has occurred at densities as great as 900 per 1 square metre (11 sq ft).[1]
Biology
Ophiura albida is a predator and scavenger and feeds on such small invertebrates as polychaete worms, crustaceans and bivalve molluscs.[1] In the Baltic Sea it is the favourite food of the starfish Luidia sarsi and is chosen in preference to other brittle stars.[4] In the Irish Sea it is eaten along with the common brittle star (Ophiothrix fragilis) by the fast-moving seven armed starfish (Luidia ciliaris).[5]
Individuals of this species are either male or female. Fertilisation is external and the larvae are planktonic. It is a fast-growing brittle star and is not thought to live for more than three years.[1]
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Ophiura albida: Brief Summary
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Ophiura albida is a species of brittle star in the order Ophiurida. It is typically found on the seabed in the north eastern Atlantic Ocean and in the Mediterranean Sea and is sometimes known as the serpent's table brittle star.
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Biology
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O. albida has separate sexes, external fertilization and pelagic larvae. The maximum age is estimated at 3 years. This shortlived species shows a relatively fast-growing strategy. O. albida may be particularly vulnerable to predation. It shows a high reproductive effort, thus maintaining the populations (Wolff, 1973; Fish & Fish, 1989; Gage, 1990). The species moves freely on the sediment (Mortensen, 1927). Small invertebrates, particularly polychaetes, bivalve mollucs and crustaceans, comprise the main food of Ophiura spp. There is evidence that scavenging and surface deposit feeding are also fairly frequent (Wolff, 1973; Warner, 1982; Fish & Fish, 1989). Young stages of trematodes and nematodes can be found in the body cavity of this brittle star (Mortensen, 1927).
Holtmann, S.E.; Groenewold, A.; Schrader, K.H.M.; Asjes, J.; Craeymeersch, J.A.; Duineveld, G.C.A.; van Bostelen, A.J.; van der Meer, J. (1996). Atlas of the zoobenthos of the Dutch continental shelf. Ministry of Transport, Public Works and Water Management: Rijswijk, The Netherlands. ISBN 90-369-4301-9. 243 pp.
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Breeding
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Ophiopluteus larva. Summer
Description
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Brittle stars consist of a central disc clearly separated from the slender, very agile and very strong arms. Ophiura albida is very similar to Ophiura ophiura and can be distinguished from this species by the absence of pores between the arm plates and by its fewer arm comb papillae. The top is reddish to orange-brown; the bottom side is dirty white.
Degraer, S.; Wittoeck, J.; Appeltans, W.; Cooreman, K.; Deprez, T.; Hillewaert, H.; Hostens, K.; Mees, J.; Vanden Berghe, E.; Vincx, M. (2006). The macrobenthos atlas of the Belgian part of the North Sea. Belgian Science Policy. D/2005/1191/3. ISBN 90-810081-6-1. 164 pp.
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Distribution
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In both periods Ophiura albida was widely spread across the Belgian part of the North Sea and was only absent in the eastern coastal zone. The species was found in relatively high densities (1976-1986 period: maximum 100 ind./m2; 1994-2001 period: maximum 900 ind./m2).
Degraer, S.; Wittoeck, J.; Appeltans, W.; Cooreman, K.; Deprez, T.; Hillewaert, H.; Hostens, K.; Mees, J.; Vanden Berghe, E.; Vincx, M. (2006). The macrobenthos atlas of the Belgian part of the North Sea. Belgian Science Policy. D/2005/1191/3. ISBN 90-810081-6-1. 164 pp.
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Distribution
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From about 10 to more than 200 m depth, common on sand, muddy sand and fine gravel, all round the British Isles
Habitat
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O. albida lives in areas with a variety of sand and muddy sand deposits.
Holtmann, S.E.; Groenewold, A.; Schrader, K.H.M.; Asjes, J.; Craeymeersch, J.A.; Duineveld, G.C.A.; van Bostelen, A.J.; van der Meer, J. (1996). Atlas of the zoobenthos of the Dutch continental shelf. Ministry of Transport, Public Works and Water Management: Rijswijk, The Netherlands. ISBN 90-369-4301-9. 243 pp.
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Habitat
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Ophiura albida prefers fine to coarse-grained sediments (median grain size 150-650 µm) without any preference for a particular median grain size. The species furthermore prefers sediments with a low to medium mud content (maximum 40%).
Degraer, S.; Wittoeck, J.; Appeltans, W.; Cooreman, K.; Deprez, T.; Hillewaert, H.; Hostens, K.; Mees, J.; Vanden Berghe, E.; Vincx, M. (2006). The macrobenthos atlas of the Belgian part of the North Sea. Belgian Science Policy. D/2005/1191/3. ISBN 90-810081-6-1. 164 pp.
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Morphology
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O. albida has a disk with rather coarse scales. The diameter of the disk can be up to 15 mm. The arms are about four times the diameter of the disk. The dorsal and ventral arm plates have a convex outer edge. The mouth shield is small, approximately one-third of the disk radius. In contrast to O. texturata (q.v.) there are no pores present between the lower arm plates. The colour of the dorsal surface usually is reddish-brown, that of the radial shields whitish (Mortensen, 1927; Southward, 1972; Gage, 1990; Hayward & Ryland, 1990).
Holtmann, S.E.; Groenewold, A.; Schrader, K.H.M.; Asjes, J.; Craeymeersch, J.A.; Duineveld, G.C.A.; van Bostelen, A.J.; van der Meer, J. (1996). Atlas of the zoobenthos of the Dutch continental shelf. Ministry of Transport, Public Works and Water Management: Rijswijk, The Netherlands. ISBN 90-369-4301-9. 243 pp.
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