Guardian Nature School Contact Blog Project Noah Facebook Project Noah Twitter

A global citizen science platform
to discover, share and identify wildlife

Join Project Noah!
nature school apple icon

Nature School For Teachers - Fall 2020 Launch! visit nature school

Purple Shore Crab

Hemigrapsus nudus


Common under stones and among seaweeds from Alaska to Baja California, the Purple shore crab has a carapace (main body shell) of about 2 inches (56.2 mm.) wide in males, and one and a half inches (34 mm.) in females. The shell is smooth and convex, usually purple, but sometimes greenish yellow or reddish brown. Its easily distinguished from the slimmer, striped shore crab by the red or purplish spots on its claws.


Their diet consists mainly of diatoms and small green algae scraped from rocks. In the Monterey Bay, breeding occurs in winter; the size of the brood varies with the size of the female... to over 36,400 eggs in a 34 mm. crab.

Species ID Suggestions

Sign in to suggest organism ID

No Comments

Eva Varga
Spotted by
Eva Varga

Oregon, USA

Spotted on Jul 18, 2012
Submitted on Aug 29, 2012

Related Spottings

Asian shore crab Oregon shore crab NZ common rock crab Asian Shore Crab

Nearby Spottings

Giant Green Anemone Ochre (Purple or Pacific) Sea Star Acorn Woodpecker (granary) Black Leather Chiton
Noah Guardians
Noah Sponsors