Description: The Pacific sand crab is one of the few species specializing in the swash zone of wave-swept sandy beaches. Its body is approximately egg-shaped. The carapace has three teeth in front and is smooth except for small, transverse ridges on the anterior portion. The first 4 pereopods are flattened, not chelate, and used for digging. The fifth pereopod is slender and chelate, and is used for cleaning the gills rather than for digging. The antennal flagellum is long and featherlike (used for filter feeding), but is folded beneath the mouth parts when not being used. Carapace length to 3.5 cm. The abdomen with its elongated telson (photo) is generally held reflexed underneath the thorax, but is extended for rapid digging into the sand (movie). The abdominal segments become successively smaller posteriorly (photo) but the elongated telson is large and arrowhead or long spade-shaped (photo). Both sexes have well-developed uropods but only females have pleopods (3 pairs). Carapace is gray or greenish in color. The underside is nearly white. Eggs are orange.
How to Distinguish from Similar Species: This is the only local species of Emerita. It differs from the spiny mole crab, Blepharipoda occidentalis, which has spines on its carapace and pereopods and typically lives lower in the swash zone in California.
Geographical Range: Alaska (but rarely north of Oregon) to Chile; Argentina
Depth Range: Intertidal
Habitat: Migrate up and down with the tides on sandy, wave-swept beaches. Inhabit the swash zone where the waves sweep up the beach and then retreat again.
Biology/Natural History: This species is abundant on some California sandy beaches but is not often found as far north as Washington. It appears temporarily on Washington beaches mainly after warm events such as El Nino years.
The species is a motile filter-feeder which inhabits the upper surf swash zone on sandy beaches. When a wave sweeps in, the animal pops up and rides the wave for a few feet; then it quickly burrows rear-first into the sand using its abdomen (movie). As the wave retreats it extends its long, feathery antennae and captures plankton and detritus from the retreating wave. Within a wave or two it will again pop up and ride the wave to a new spot; thus remaining in the swash zone as the tide advances and retreats along the beach. The species primarily inhabits beaches with clean, pebble and stone-free sand. It can be detected when it pops up in shallow water behind the latest advancing wave, and also by the V-shaped wake its antennae make as it filters the retreating wave.
This species is an alternate host to several parasitic
worms that have
shorebirds as their definitive host (Bhaduri et al., 2018), including
and the trematode Microphallus
The worms live in the crab's hemocoel (body cavity) and are more
in larger crabs, especially females.
Kozloff, 1987, 1996
General Notes and Observations: Locations, abundances, unusual behaviors:
Records of my Emerita analoga sightings in Washington:
July 20, 2016: I found many juveniles on the
beach at Kalaloch,
most less than 1 cm total length. Even after searching the
strand line, which contained exoskeletons from thousands of Emerita,
I did not find any living or dead individual larger than 1.2 cm long.
Authors and Editors
Salish Sea Invertebrates web site provided courtesy of Walla