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Shore Crabs

Although shaped well to hide in cracks, shore crabs actively leave shelter to seek food.

Lined Shore Crab
Shore crabs can hunt and scavenge along the shore above the waterline because they can hold water in their bodies next to the gills, drawing on the oxygen from the stored water for some time. What if it rains? With their exoskeletons and their “above water breathing system,” shore crabs are also quite tolerant of exposure to rain and runoff.

The crabs and other animals under rocks are there because they require the protection: it’s important to replace anything you move to the original position to restore their protection.

What kind of shore crab did you find?

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More Information

Description: Shore crabs are compact and flat, with a nearly square back and legs that tuck tightly together and against the body. Our three species are generally dark and subtly patterned: fine, green stripes across the back from side to side; purple mottling on the back and spots on the claws; mottled greenish gray all over. Small (up to 2” wide) and very active, these crabs scuttle about when not hiding under rocks and in crevices.

What kind of shore crab did you find? Examine the colors and think about the location of the shore crab:

Fine green lines across the back and high on the shore? lined shore crab

Purple spots on the claws and a bit lower on the shore? purple shore crab

Mottled greenish gray and still lower on the shore? Oregon shore crab

Taxonomy:

Kingdom Animalia -- Animal, animals, animaux
Phylum Arthropoda -- arthropodes, arthropods, Artrópode
Subphylum Crustacea Brünnich, 1772 -- crustaceans, crustáceo, crustacés
Class Malacostraca Latreille, 1802
Subclass Eumalacostraca Grobben, 1892
Superorder Eucarida Calman, 1904 -- camarão, caranguejo, ermitão, lagosta, siri
Order Decapoda Latreille, 1802 -- crabes, crabs, crayfishes, crevettes, écrevisses, homards, lobsters, prawns, shrimp
Suborder Pleocyemata Burkenroad, 1963
Infraorder Brachyura Latreille, 1802 -- short-tailed crabs, true crabs

Common species:

  • Hemigrapsus nudus (Dana, 1851) -- purple shore crab
  • Hemigrapsus oregonensis (Dana, 1851) -- yellow shore crab, Oregon shore crab
  • Pachygrapsus crassipes J. W. Randall, 1840 -- striped shore crab

Taxonomic information source: ITIS.gov