they reach 3.6–5.5 cm in length, but by far most males and females reproduce when around 10 cm in diameter, when they are 1 year old. The species reproduces seasonally and spawns from January to April in Japan, from June to October in Russia, and between July and October in Australia. Females are capable of carrying up to 20 million eggs. Gametogenesis in females takes 9 months. Females spawn (release eggs) successively during the breeding season. In Japan it may spawn in two main events in the year, elsewhere it is once. Species interactions Prey It is a generalist predator, but primarily preys on large bivalve mollusc species. It pulls their wings apart with all five arms and then everts its stomach into the shell. It can dig clams out of the seabed on occasion. It can be selective or opportunistic depending on availability of prey. It sometimes also preys on gastropods, crabs, barnacles, ascidians, sea squirts and algae. It has also been seen preying on itself during periods of low food abundance. It will also eat dead fish and fish waste. In Tasmania it preys on the egg masses of the spotted handfish and the ascidians on which they spawn. Predators In Japan, the sunstar Solaster paxillatus eats this species. It is preyed upon by the spiny sand seastar Luidia quinaria in Tokyo Bay. In aquaria in Alaska, king crabs (Paralithodes camtschaticus) were recorded feeding on this seastar. In laboratory experiments in Korea, Charonia sp. (trumpet snail) were found to prefer this species above other seastars, sea cucumbers and sea urchins. Parasites In Japan, the scuticociliates Orchitophrya stellarum and another Orchitophrya sp. are known to parasitise the gonads of this seastar, especially the males. O. stellarum infects testes and feeds on the gonads of various seastar species. It can cause castration and be lethal for Asterias amurensis in Japan. Other possible parasites found associated with these seastars are the skeleton shrimps Caprella astericola, the copepod Scottomyzon gibberum, the polychaete scaleworm Arctonoe uittuta, species from the harpacticoid copepods genera Parathalestris, Thalestris, Paramphiacella and Eupelite, as well as several unidentified gammaridean amphipods and an unidentified apicomplexan living within it. Other In Japan it is abundant at 20m depth, but decreases to 50m, where it is replaced by another seastar species, Distolasterias nipon. It competes with the starfish Uniophora granifera and Coscinasterias muricata, and Pacific walruses, Odobenus rosmarus ssp. divergens, for bivalve