Emerita analoga (Stimpson, 1857)

Common name(s): Pacific sand crab, sand crab,  mole crab

Synonyms: Hippa analoga 3 cm preserved female
Phylum Arthropoda 
Subphylum Crustacea 
Class Malacostraca 
Subclass Eumalacostraca 
Superorder Eucarida 
Order Decapoda 
Suborder Pleocyemata 
Superfamily Hippoidea 
Family Hippidae 
A preserved female, 3 cm carapace length, collected at Monterey Bay. Note that the normal gray color has faded because this is a preserved specimen. This female is carrying eggs (see photo below).
(Photo by:  Dave Cowles, July 2016)

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.



 

References:

Dichotomous Keys:
  Carlton, 2007
  Kozloff, 1987, 1996

General References:
  Hart, 1982
  Jensen, 1995
  Jensen, 2014
  Johnson and Snook, 1955
  Kozloff, 1993
  Lamb and Hanby, 2005
  Morris et al., 1980
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:
 

Web sites:


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 high-tide strand line, which contained exoskeletons from thousands of Emerita, I did not find any living or dead individual larger than 1.2 cm long.
 
Two views of the ventral side of a 3 cm carapace length preserved female from Monterey Bay, CA.  The left view shows the normal position of the abdomen and telson. On the right, the telson is held out to reveal the eggs held on the pleopods. Note that the normal color has faded since this is a preserved specimen.
Ventral-normal position Abdomen open to reveal eggs

Dorsal and ventral views of a preserved male, 2.7 cm carapace length.  In both views the abdomen has been artificially extended. Note the lack of pleopods on the abdomen.  Since this is a preserved specimen the true color has faded.
Male dorsal Male ventral


Head
A closeup view of the head of the 3 cm carapace length preserved female

Click Here for a movie of a 1.2 cm total-length juvenile rapidly digging into the damp sand just above the wave swash zone after I dropped it onto the sand. 
 
 
 
These two photos show a live, mature female female Emerita analoga captured from the swash zone of the sandy beach at Warrenton, OR just south of the Columbia River in late August, 2017. Total animal length is 4.5 cm. Photos by Dave Cowles
Dorsal view Ventral side
Dorsal view. Note how the carapace is egg-shaped and the animal keeps its legs and other appendages folded underneath, maintaining a 3-dimensional egg-like contour. The head is to the right in this photo. Ventral view. Note how the abdomen with lits arge, pointed telson is folded loosely underneath the body. The abdomen and telson are used for rapid digging into the sand as each wave begins to recede. She is carrying a batch of orange eggs on her pleopods underneath the telson.  Her head, with its feathery antennae, is on the right.


Authors and Editors of Page:
Dave Cowles (2016):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)

Salish Sea Invertebrates web site provided courtesy of Walla Walla University