THE STEINHART AQUARIUM - Gulf of Guinea Science ...

The mollusk shells selected as homes for this
otherwise naked crustacean are typically coated
with diminutive sea anemones (Calliactis spp.).
This symbiotic pairing provides protection
and camouflage for the hermit, and gives the
hitchhiking anemones food shared with the crab.
When disturbed, the anemones aboard for the
free ride expel acontia (lengthy stinging cells).
Hermit crabs have been observed transferring
their hitchhikers to a new shell when they
outgrow their home!
Naked or Pacific Mole Crab
Emerita analoga (Hippidae)
Distribution: Pacific coast from Alaska to Baja
California and from Ecuador to Argentina.
Habitat: The swash zone of the sandy intertidal
beach, which ranges from the lowest to highest
reaches of the waves at any given time. The
swash zone changes with the tides, and so does
the location of the mole crabs
Appearance: Gray or sand-colored crab that
lacks claws or spines. Females are larger than
males. Swims, crawls, and burrows, always
moving backwards, using its five pairs of legs.
Hairs on appendages aid in rapid movement
through the sand. First pair of antennae reach
above the sand for respiration, and eyes with
long stalks often extend above the sand as well.
Diet: Small organisms, mostly diatoms. When
the sand is covered by a wave, the second
pair of antennae are extended above the sand
to collect these tiny organisms, which are
brought toward the mouth and scraped off.
The movement is quick; a mole crab can make
several passes for food in one receding wave.
Reproduction and Development: Females
produce about one clutch of eggs per month,
which she carries, like many crab species,
attached on her abdomen beneath the
telson until they hatch. Planktonic larvae
metamorphose through multiple stage, often
traveling far offshore until some successfully
settle onto beaches.
Mortality/Longevity: A major food source for
shorebirds and some fish species of the surf
zone, such as barred surfperch. Also eaten by
sea otters.
Remarks: Mole crabs are found on the beach
in large numbers from spring to fall. In winter,
storms carry them to offshore sandbars.
California Academy of Sciences
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Used as bait by shore fishermen.
Mole crabs are collected to indicate levels of
DDT and neurotoxins produced seasonally
by diatoms, substances that are toxic to birds,
otters, and fish that eat them.
Hermit Crab
Pagurus spp. (Paguridae)
Distribution: Some species in this genus occur
in northern Japan, the Bering Strait, and south
to Baja California.
Habitat: Tide pools in upper to middle intertidal
zones. Some species reported to more
than 110 m depth.
Appearance: These clever crabs appropriate
gastropod mollusk shells into defensive homes.
On our seacoast there are typically 4 species of
hermits in the intertidal. Their appearance is
most obviously recognized by their appropriated
shell (Tegula is a popular choice).
Diet: Scavenge dead algae and animal matter.
Reproduction and Development: : Sexes separate,
fertilization is internal. The male often
grasps the edge of the female’s shell and drags
it around with him, waiting for the female to
molt, after which he deposits sperm on her
abdomen. Females carry eggs and then release
planktonic larvae. Once they have outgrown
their home due to weight gain they select a
larger, empty shell.
Mortality/Longevity: Preyed upon by fishes,
crabs, and sea anemones.
Remarks: Hermit crabs (Anomura) have 3 pairs
of walking legs. True crabs (Brachyura) have a
pair of claws and 4 pairs of walking legs.
Their abdomens are long, slender, soft and
usually flexed to the right which allows them
to fit into old snail shells, which are practically
all right handed.
Black-eyed Hermit Crab
Pagurus armatus (Paguridae)
Distribution: Coastal areas of the Pacific
Northwest from Alaska, British Columbia,
the Puget Sound area of Washington south to
California.
Habitat: Found on a variety of substrates, from
muddy areas to protected sandy bottoms from
the intertidal zone to depths of 120 m.
Appearance: One of the largest species of
hermit crabs. Easily identified by its large, oval,