Phylum Arthropoda, Subph. Crustacea: Rocky Shore Crabs, Shrimp, Isopods, Amphipods

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Pachygrapsus crassipes
Pachygrapsus crassipes Randall, 1839
Phylum Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Eucarida, Order Decapoda,  Infraorder Brachyura, Family Grapsidae

Lined shore crab; carapace trapezoidal with 2 antero-lateral teeth on each side; dark green-black with red or purple highlights on appendages; broken transverse lines across top of carapace, 40-45 mm across.

Abundant, but fast, cryptic & pugnacious; high to mid-intertidal zone, exposed & protected outer coast; feeds on algal films & scavenges.

Geogr. Range: central Oregon to Baja
Synonyms:
Similar species: Hemigrapsus nudus has purple spots on chelae.

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Hemigrapsus nudus
Hemigrapsus nudus (Dana, 1851)
Phylum
Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Eucarida, Order Decapoda, Infraorder Brachyura, Family Varunidae

Purple shore crab; carapace a rounded square lacking horizontal lines, 35-50 mm across; purple, yellow- green, red-brown; usually with purple spots on chelae.

Moderately common; more sluggish & less aggressive than Pachygrapsus; under rocks & among seaweeds; mid- to low intertidal zone, protected outer coast.

Geogr. Range: Alaska to Baja (uncommon south of Morro Bay
Synonyms:
Similar species: Pachygrapsus crassipes has horizontal lines on carapace & no spots on claws.

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juvenile Cancer
Cancer antennarius  Stimpson, 1856
Phylum Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Eucarida, Order Decapoda, Infraorder Brachyura, Family Cancridae

Adults 15-18 cm across reddish-brown carapace; claws tipped with black; underside of body with red spots; juvenile carapace usually covered with hairs. 

Common, but cryptic under rocks and algae; low intertidal zone & subtidal, protected outer coast. Preys on hard-shelled prey (snails, clams, etc).

Geogr. Range: British Columbia to Cabo San Lucas, Baja
Synonyms:
Similar species: Cancer productus is also reddish with black-tipped claws, but it lacks red spots on ventral side & the teeth on its carapace are broader & rounder; its juveniles often have a striking zebra-stripe color pattern that is lacking in C. antennarius.

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Petrolisthes cinctipes
Petrolisthes cinctipes (Randall, 1840)
Phylum Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Eucarida, Order Decapoda, Infraorder Anomura, Family Porcellanidae

Porcelain crab; 3 pr. walking legs with 1 pr. broad flat claws; carapace square, antennae dk. red; carapace to 24 mm, lacks hairs; color light brown to dk. brown; mouth parts bright red; red-orange spot at base of dactyl on claws; readily autotomizes appendages when disturbed.

Abundant under rocks, high to mid-intertidal zones; protected outer coast. Suspension feeder.

Geogr. Range: British Columbia to Santa Barbara, Calif.
Synonyms:
Similar species: Petrolisthes eriomerusP. manimaculus have more slender claws & occur lower on the shore

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Pagurus samuelis
Pagurus samuelis (Stimpson, 1857)
Phylum Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Eucarida, Order Decapoda, Infraorder Anomura, Family Paguridae

Hermit crab; antennae red & unbanded; irregular patches of blue on tips of legs; small juveniles often with white bands on legs; carapace to 19 mm; dark olive green.

Most common hermit crab in tidepools; high to mid-intertidal zones; protected outer coast; prefers turban snail shells.

Geogr. Range: Vancouver Island to Baja
Synonyms:
Similar species: Pagurus granosimanus has blue or white bumps on carapace & claws; numerous spp. of hermit crabs occur in tidepools.

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Pagurus granosimanus
Pagurus granosimanus  (Stimpson, 1859)
Phylum Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Eucarida, Order Decapoda, Infraorder Anomura, Family Paguridae

Hermit crab; antennae red-orange, unbanded; dark olive green with blue or white wart-like granules, especially on chelae & walking legs.

Common, in tidepools, lower mid- to low intertidal & subtidal. 

Geogr. Range: Aleutian Islands, Alaska to Baja
Synonyms:
Similar species: Pagurus samuelis lacks blue or white granules on legs & claws; numerous spp. of hermit crabs occur in tidepools.

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Cirolana harfordi
Cirolana harfordi  (Lockinton, 1877)
Phylum Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Peracarida, Order Isopoda, Family Cirolanidae

Isopod; oval, dorsoventrally-compressed body to 20 mm (most closer to 10 mm), pale gray or tan to black.

Abundant, under rocks resting in sand or gravel; also in mussel beds; mid-intertidal zone, exposed & protected outer coast; voracious scavenger / predator.

Geogr. Range: British Columbia to Baja
Synonyms:
Similar species: many other spp. of isopods occur on rocky shores.

Image: juvenile Chlorostoma funebralis (middle rt.)

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Ligia occidentalis
Ligia occidentalis  Dana, 1853
Phylum Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Peracarida, Order Isopoda, Family Ligiidae

High-shore isopod; dorsoventally-compressed body to 25 mm; elongate uropods (specimen in photo missing 1 uropod).

Common, under stones & in crevices; high intertidal zone well above the highest tides; spends most of time out of the water, returning only to wet its gills; extremely quick and agile.

Geogr. Range: Sonoma County to Central America
Synonyms:
Similar species: many other spp. of isopods occur on rocky shores.

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Page created by J.M. Watanabe
All images copyright James Watanabe unless otherwise indicated
Contact:  watanabe_at_stanford_dot_edu                                                                                                                                   Last  update: 11 March 2010