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Crustaceans - crabs, shrimp, isopods, amphipods


Pachygrapsus crassipesPachygrapsus 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 nudusHemigrapsus 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.

 

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Romaleon antennariumRomaleon 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.

 

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Petrolisthes cinctipesPetrolisthes 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

 

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Pagurus samuelisPagurus 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 granosimanusPagurus 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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Pleuroncodes planipePleuroncodes 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.

 

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Cirolana harfordiCirolana 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 occidentalisLigia 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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