Mottled Star

Appearance

The mottled star is a large starfish with a radius of up to 28 centimetres. 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 surface of the disc is covered with a network of calcareous plates with spines about 2 mm long surrounded by smaller spines and crossed and straight pedicellariae, minute pincer-like structures with two 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 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.

Naming

The scale worm "Arctonoe fragilis" is often found living on the surface or in an ambulacral groove of the mottled star as a commensal. The parasitic ciliate "Orchitophrya stellarum" has several hosts, one of which is the mottled star. It lives among the spines on the body and arms until the starfish is ready to breed when it moves inside its host, probably entering through a gonopore. It makes its way to the gonads of the male starfish and feeds on the sperm, effectively castrating its host.

Juvenile Alaskan king crabs " have been observed living as commensals on the surface of the mottled star, sheltering between its arms. Adult king crabs have been reported as attacking and eating the starfish. It is also preyed on by gulls in the intertidal zone and by the morning sunstar and the sunflower seastar.

Distribution

"Evasterias troschelii" 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 or 70 metres. In bays and other sheltered locations it largely replaces the other common species of the area, the purple sea star.

Habitat

"Evasterias troschelii" 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 or 70 metres. In bays and other sheltered locations it largely replaces the other common species of the area, the purple sea star.

Reproduction

In the north of its range, breeding takes place from April to June. Large numbers of small eggs are produced and fertilisation is external. The bipinnaria larvae that develop from these form part of the zooplankton and disperse with the currents.