Extremely small crabs, Hemigrapsus oregonensis have a dark reddish-brown shell with equally dark green blotches (1). Their carapaces lack any distinguishing characteristics and exhibit sexual dimorphism; with males noticeably larger than females (1). Chelipeds for this crab have white or yellow tips (1) and are often used in behavioral patterns (3). While they are opertunisitic omnivores, their size makes them easy prey for birds and other crabs. As a result they are often found under rocks or shells in intertidal zones or in burrows nearshore (4). H. oregonensis have a large number of setae on their legs, facilitating gas exchange allow them to survive in muddy or even anoxic environments (4).
(1) Cowles, Dave. "Hemigrapsus oregonensis (Dana, 1851)." Invertebrates of the Salish Sea. 2005. https://inverts.wallawalla.edu/Arthropoda/Crustacea/Malacostraca/Eumalac....
(2) Hemigrapsus oregonensis (Dana, 1851). ITIS Standard Report Page: Hemigrapsus oregonensis. https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search...
(3) Lindberg WJ. Behavior of the Oregon Mud Crab, Hemigrapsus Oregonensis (Dana) (Brachyura, Grapsidae). Crustaceana. 1980;39(3):263–281.
(4) Willason SW. Factors influencing the distribution and coexistence of Pachygrapsus crassipes and Hemigrapsus oregonensis (Decapoda: Grapsidae) in a California salt marsh. Marine Biology. 1981;64(2):125–133.
- rocky intertidal