Helmet Crab

How to Distinguish from Similar Species: This is the only member of Family Atelecyclidae in this area, and the only local species with a 5-sided carapace.

Eelgrass, algae, soft bottoms, sometimes on rocky bottoms.

Geographical Range: Bering Sea to California, and to Siberia, Japan, and Korea. Not common on our coast south of Washington.

Depth Range: Intertidal to 110 meters. Mostly subtidal.

A true crab without a rostrum, but with several distinct teeth between the eyes and along the anterolateral margins of the carapace. Marginal teeth have several spines. Setae are stiff and club-shaped. Abdomen of male has 6 segments plus the telson. The carapace is 5-sided. The chelipeds are relatively short--shorter than the long walking legs. The right cheliped is usually larger than the left. Color usually a greenish or brownish yellow; may have red or orange spots and margin. Carapace width to 97 mm and 102 mm

Biology/Natural History: This species is mostly subtidal but can be found in the eelgrass at very low tides at Padilla Bay. It can bury itself in the sediment. Eats a variety of food, such as eelgrass, eelgrass detritus, snails, algae, worms, and bivalves. Predators include sea otters and fur seals, the rosylip sculpin, and gulls, which catch them in eelgrass beds at low tide, flip them over, and eat their insides. Comes to intertidal algae-covered rocks in spring or early summer for mating, which occurs just after the female molts. In Hokkaido, Japan, mating occurs in May and June. Nagao and Munehara found that in Japan adult females of this species store sperm from one mating season to the next. Females isolated from males during a mating season nevertheless laid fertile eggs by fertilizing them with sperm stored from the previous season.