Armed Hermit Crab

Usually on sand, mud, shell, or gravel bottoms.

Geographical Range: Northern Alaska to southern California

Depth Range: Intertidal to 146 m; usually subtidal

This hermit crab has a carapace which is smooth and only the shield is calcified. The abdomen is asymmetrically coiled. The carpus of the right cheliped is longer than wide. The cheliped is shorter than the walking legs. The dactyls of legs 2 and 3 are longer than the merus, twisted in relation to the propodus, and have 2 reddish-brown stripes. The upper margin of the dactyl is serrated and the lower margin has close-set corneous spines. The merus of the walking legs is compressed laterally, with spines and toothed ridges. The carpus and propodus of the walking legs have serrated dorsal margins and small spines on the surface. The chelipeds are spiny dorsally and marginally but are nearly smooth ventrally. The dorsal side of the left cheliped is flat. The eystalks are short and the eyes are large and black. The legs and chelipeds have orange transverse bands. The ischium of the chelipeds has brown bands, the merus is pink, brown, and white with brown margins and teeth plus an orange distal band. The palm of the propodus is pale yellow. It has dark brown medial spines and red marginal spines. The finger of the propodus is white or gray-blue with a white tip and white teeth. The walking legs have a yellow and white ischium, a merus with white, tan, orange, and mahogany with scattered brown spots; a yellow carpus with dark spines plus a mahogany stripe posteriorly and a white patch near the end, a propodus with white, yellow, orange, and brown and a mahogany stripe, and a dactyl which is white, orange, and violet-blue with dark spines and two narrow brownish-red stripes. The legs have a green or gold iridescent sheen to them. The eyestalks have a red band at the base and white and brown bands. The antennal flagellum is pale yellow. Carapace shield length to 19.6 mm and total carapace length up to 4.5 cm.

How to Distinguish from Similar Species: The large black eyes plus orange bands on the legs are distinctive. P. aleuticus and P. ochotensis have spines on the ventral side of the chelipeds, plus P. ochotensis has greenish-yellow eyes. Most other hermit crabs do not have the twisted dactyls on legs 2 and 3.

Biology/Natural History: This is one of the largest and most common hermit crabs found in subtidal sandy areas. As seen in many other crab species, males carry females around prior to the female molting so that they can mate. This species can grow large and often lives in moon snail shells,Euspira lewisii. Small individuals may have shells covered with hydroids and have partly yellow eyes. It is often found among sea pens in Puget Sound. Females may carry up to three broods of eggs per year.