crabs have a variety of associations
with other marine creatures. To what
degree this arrangement advantages each
animal involved depends on the specific
is the sulphur sponge Suberites domuncula
which grows on mollusc shells inhabited
by hermit crabs. The sponge may eventually
eat away the shell leaving the hermit
crab completely dependant on the sponge
for protection. This is a mutualistic
or symbiotic association, with both
sides gaining. The sessile sponge is
now mobile being carried by the crab.
The crab is camouflaged plus there is
the additional benefit of the sponge’s
unpleasant taste and smell which deters
commonly lives in the shell with the
hermit crab. In this case the ragworm
benefits, as when the hermit crab finds
food, the worm also feeds, plus it has
the protection of the shell. It is unclear
how the hermit benefits from this association
but the relationship is not detrimental.
Such a relationship is commensal. Another
common commensal association is that
with the hydroid Hydractinia echinata.
The hydroid appears as furry growths
on the hermit crab’s shell home.
is a parasitic association of that with
the Peltogaster paguri a parasitic
barnacle. This association benefits
one partner but is detrimental to another.
The barnacle is rarely seen as it lives
on the abdomens of hermit crabs situated
within the shells.
most well known associations are those
between hermit crabs and sea anemones.
Unfortunately the majority of the hermit
crabs seen on the shore do not carry
sea anemones, it is usually the more
mature adults, which may be seen at
the lowest tides in the sublittoral
zone but are mainly in shallow water.
the parties benefit from these associations.
The hermit crab is protected by the
stinging tentacles of the sea anemone.
The sea anemone derives feeding opportunities
by catching fragments of food produced
as the hermit crab eats, and mobility.
The common hermit crab is often associated
with the sea anemone Calliactis parasitica,
the name is a misnomer as it is not
parasitic. Pagurus prideauxi
lives in association with Adamsia
most common species in Cornwall is the
Common Hermit Crab Eupagurus bernhardus.
They are commonly seen moving in rock
pools, and at first glance will be taken
as a mollusc. With closer observation,
their gait gives them away. They can
reach up to four inches in length, at
this stage only a large whelk shell
will suffice. Large specimens are not
normally found on the shore as they
tend to move into shallow water.
not so common species, Pagurus prideauxi,
also occurs in Cornwall. Not often seen
on the shore, as it is a sublittoral
species, living on sandy bottoms. It
does not grow as large as the common
hermit crab, only reaching two and a
half inches in length.