Flat porcelain crab • Petrolisthes cinctipes
Identification
The flat porcelain crab is a small porcelain crab (carapace to 2.5 cm wide) that varies in colour from light to dark brown and occasionally blue. It is flattened and has broad, flat, even-sized claws. Its main identifying features are reddish-orange mouth parts and reddish-orange spots at the joint of the pincers (chela) - this location is also called the thumb joint. In order to obtain a correct identification the claws or mouth must be open to reveal this colouration. The antennae are dark red.
Habitat & Range
This crab can be found under rocks in the upper and middle intertidal of shorelines near or on an exposed outer coast. Its range extends from Porcher Island in northern BC to southern California.
Similar Species
The flattop crab (Petrolisthes eriomerus) is more common in sheltered waters. It has blue mouth parts and claw spots as opposed to the orangey-red mouth parts and claw spots of the flat porcelain crab.
Intriguing Info
The flat porcelain crab can be very abundant in California mussel (Mytilus californianus) beds. It avoids hiding under rocks that rest on fine sediment and so is usually restricted to the upper and middle intertidal. It is competitively superior to the flattop crab, however the latter is restricted to the lower intertidal as it can't tolerate exposure to warm air temperatures.
Porcelain crabs are named so because of their tendency to release legs readily, or "break" like porcelain, when disturbed.
iNaturalist
https://www.inaturalist.org/taxa/53620-Petrolisthes-cinctipes
The flat porcelain crab is a small porcelain crab (carapace to 2.5 cm wide) that varies in colour from light to dark brown and occasionally blue. It is flattened and has broad, flat, even-sized claws. Its main identifying features are reddish-orange mouth parts and reddish-orange spots at the joint of the pincers (chela) - this location is also called the thumb joint. In order to obtain a correct identification the claws or mouth must be open to reveal this colouration. The antennae are dark red.
Habitat & Range
This crab can be found under rocks in the upper and middle intertidal of shorelines near or on an exposed outer coast. Its range extends from Porcher Island in northern BC to southern California.
Similar Species
The flattop crab (Petrolisthes eriomerus) is more common in sheltered waters. It has blue mouth parts and claw spots as opposed to the orangey-red mouth parts and claw spots of the flat porcelain crab.
Intriguing Info
The flat porcelain crab can be very abundant in California mussel (Mytilus californianus) beds. It avoids hiding under rocks that rest on fine sediment and so is usually restricted to the upper and middle intertidal. It is competitively superior to the flattop crab, however the latter is restricted to the lower intertidal as it can't tolerate exposure to warm air temperatures.
Porcelain crabs are named so because of their tendency to release legs readily, or "break" like porcelain, when disturbed.
iNaturalist
https://www.inaturalist.org/taxa/53620-Petrolisthes-cinctipes
References
Harbo, R. M. (2011). Whelks to whales: Coastal marine life of the Pacific Northwest. Madeira Park, BC: Harbour Publishing. P.101.
Jensen, G.C. (1995). Pacific Coast Crabs and Shrimps. Monterey, CA: Sea Challengers. P. 75.
Lamb, A., and Hanby, B. (2005). Marine Life of the Pacific Northwest [electronic resource]. Madeira Park, BC: Harbour Publishing.
Authors and editors of page
Kelly Fretwell and Brian Starzomski (2014).
Harbo, R. M. (2011). Whelks to whales: Coastal marine life of the Pacific Northwest. Madeira Park, BC: Harbour Publishing. P.101.
Jensen, G.C. (1995). Pacific Coast Crabs and Shrimps. Monterey, CA: Sea Challengers. P. 75.
Lamb, A., and Hanby, B. (2005). Marine Life of the Pacific Northwest [electronic resource]. Madeira Park, BC: Harbour Publishing.
Authors and editors of page
Kelly Fretwell and Brian Starzomski (2014).