Evasterias troscheli
| Evasterias troscheli | |
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| Close-up of the disc and madreporite | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | Asteroidea |
| Order: | Forcipulatida |
| Family: | Asteriidae |
| Genus: | Evasterias |
| Species: | E. troscheli |
| Binomial name | |
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Evasterias troscheli (Stimpson, 1862) |
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Evasterias troscheli is a species of starfish in the family Asteriidae. Its common names include the mottled star, false ochre sea star and Troschell's true star. It is found in Kamchatka and the north western coast of North America.
The mottled star is a large starfish with a radius of up to 28 centimetres (11 in). It has a small disc and five long narrow arms often turned up at the tip. The widest point of the arms is a little distance away from the edge of the disc. The aboral (upper) surface of the disc is covered with a network of calcareous plates with spines about 2 mm (0.1 in) long surrounded by smaller spines and crossed and straight pedicellariae, minute pincer-like structures with 3 jaws. There is an irregular line of white-tipped spines running down the centre of the arms and the whole upper surface is rough to the touch. On the oral (lower) surface a long ambulacral groove stretches from the central mouth to the tip of each arm with four rows of tube feet and clumps of pedicellariae and spines on either side. The colour is very variable and includes plain or mottled shades of orange, brown, greenish-grey, bluish-grey and pale purple. The outer edges of the arms often have a contrasting coloured rim and the underside is pale brown.
The mottled star is found on the west coast of North America. Its range extends from Pribilof Islands, Alaska southwards to Monterey Bay, California but it is rarely seen south of Puget Sound. It also occurs in Kamchatka. It is usually found on rocks and pebbles and occasionally on sand, at depths down to about 75 metres (246 ft). In bays and other sheltered locations it largely replaces the other common species of the area, the purple sea star (Pisaster ochraceus).
The mottled star is a predator and feeds largely on bivalve molluscs. With its tube feet it can exert a powerful traction on the two valves of a mollusc shell, pulling them sufficiently far apart to insert part of its stomach through the gap. It then uses digestive enzymes to break down the mollusc's tissues before sucking them out and removing its stomach from the shell. It also consumes barnacles, chitons, gastropod molluscs, tunicates and brachiopods. Some species of limpet exhibit behavioural responses to the presence of the mottled star and are able to evade it.
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Wikipedia