THE SEA saone
45
'
‘
association called “
commensalism,” which may be"dëëd ’
.
as an external partnership between two di‘erent‘animals'
usually-«for their
a0n the shore the “most
-
,
striking example is furnished by" the association between the
'
hermit crabs and different kinds of anemones and sponges.
One species of hermit, Eupagurus prideauxi, is alwaysfound
with its body enfolded by an anemone, Adaänsia palliatd,
which resembles a sausage—shaped bag pushed in at either
end, to form, at the upper end the stomach cavity, the mouth
of which is surrounded by tentacles, and at the lower end
the much larger cavity occupied __by the soft body of the
crab.
A mollùsc shell is always present in the rSt place and
to this the crab is attached.
Thé common shbre
bernhardus, which lives in shèllsof all sizes up to those of the
whelk, usually carries on the shell a large anemone, Sagaïtia
‘
parasitica, while in the-upper whorls of the shell there is
‘
often a worm called Nereilepas.
'
Yet a third, smaller
hermit, E. pubescens, is 'often almost obscured by the
'
relatively large masses of a _spor‘1ge Which. almost invariably ‘
grows on the shell.
This déhite association between the
hermit and the
and
sponge 15
clearly not
*
accidental, in the former case the anemone probably helps
to protect the hermit which, in turn, provides the anemone
with scraps of
in,the- latter case the sponge-=may
provide pr0tection by camouage ”and ' itself receive
-
‘
‘
,
Other examples of commensälism are provided by the
gall crabs which live
The' yjou‘ng female crab
séttles down between two branches of the coral, which as
a result, broadei1 and nally unite above the crab, forming
a gall Within which the crab lives, feeding, not on the coral,
but
brought in by the water.
The male of
the
outside. the coral:
pee. crab,
which lives in bivalves and sea sçiuirts, is a further example.