Crustaceans - crabs, shrimp, isopods, amphipods

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.

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 trapezoid 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.

Romaleon antennarium  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:  Cancer antennarius
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 R. antennarium.

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 eriomerus & P. manimaculus have more slender claws & occur lower on the shore

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.

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.

Pleuroncodes planipe  Stimpson, 1860
Phylum Arthropoda, Subph. Crustacea, Class Malacostraca, Subcl. Eumalacostraca, Superorder Eucarida, Order Decapoda, Suborder Pleocyemata, Infraorder Anomura, Family Galatheidae

Pelagic red crab.  Carapace length to 5 cm, bright red; long narrow chelae; short abdomen folded under thorax; 5th pr. of thoracic legs reduced in size.  

Uncommon in central California, except in El Niño years.  Typically on sandy substrate 45-90 m depth or swimming in water column, feeding on copepods & other small planktonic organisms.   Mass strandings often occur on beaches during El Niño years.

Geogr. Range: Baja California, occasionally in southern & central Calif. as far north as San Francisco during warm years.
Synonyms:
Similar species: Munida has longer, more slender claws.

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.)

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.