| Seven-armed starfish | |
|---|---|
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Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | Asteroidea |
| Order: | Paxillosida |
| Family: | Luidiidae |
| Genus: | Luidia |
| Species: | L. ciliaris |
| Binomial name | |
| Luidia ciliaris | |
| Synonyms[1] | |
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Luidia ciliaris, theseven-armed sea star, is aspecies ofsea star (starfish) in the familyLuidiidae. It is found in the easternAtlantic Ocean and theMediterranean Sea.[1]
L. ciliaris is an orangeish-brown colour and has seven long arms radiating from a small disk. It is a large but fragile sea star, growing to 40 cm (16 in) across, and easily losing its arms (which afterwards regenerate). The arms have parallel sides and taper only near the tip. They have a conspicuous fringe of white spines along the margins. The upper surface is clothed inpaxillae, spines shaped like a pillar with a flat top bearing tiny spinules. Also, many-lobed, nipple-like papillae are seen. No marginal plates are on the upper side of the arms, but those on the lower side bearpedicellariae with two valves. Thetube feet are long and numerous. They do not have suction pads, but have two sets of terminal bulbs. Thegonads are arranged in two rows along the length of the arms. A mouth is at the centre of the underside, with an oesophagus and a cardiac stomach, but no intestine, pyloric stomach, or anus.[2][3]
L. ciliaris occurs on theseabed in the easternAtlantic Ocean fromNorway and theFaroe Islands southwards toCape Verde and theAzores and in theMediterranean Sea. It is found in theneritic zone at depths down to 400 m (1,300 ft), mainly on soft sediments into which it sometimes burrows, but sometimes on rock.[1][3]
L. ciliaris is apredator andscavenger and feeds predominantly on otherechinoderms. A study in the Irish Sea found that thebrittle stars,Ophiothrix fragilis andOphiura albida, and thesea urchin,Psammechinus miliaris, formed the chief items of prey. The brittle starOphiocomina nigra was also consumed, but in lesser quantities because it had more efficient escape strategies.[4]
The seven-armed sea star moves rapidly in comparison with other sea stars. It hoists itself up on the tips of its arms, in which position it can "walk",[5] before launching itself at itsprey. The ring of plates around its mouth are extensible or can even be ruptured to enable it to ingest food items much bigger than the normal size of its mouth. In this way, it can pounce on a brittle star 25 cm (9.8 in) in diameter and completely engulf it. Undigested remains are ejected through the mouth.[5]
L. ciliaris breeds in early summer. Each female releases millions ofeggs into thewater column, which stimulates the release of sperm by the males. About 4 days after fertilisation, thezygotes develop intobipinnarial larvae, which form part of theplankton. After several moults, the seven arms can be seen developing in what is called the "rudiment", which is connected to a stalk with several bands ofcilia. The larvae reach a length of 35 mm (1.4 in) in 3 to 4 months.[6] It does not become abrachiolarial larva as is the case in most sea startaxa. Instead, it settles on the sea bed andmetamorphosis takes place. Functional tube feet appear in the juvenile before the larval tissue is fully reabsorbed.[5][7]