The so-called carcinium or hermit crab is in a way intermediate
between the crustaceans and the testaceans. In its nature it resembles
the crawfish kind, and it is born simple of itself, but by its habit
of introducing itself into a shell and living there it resembles the
testaceans, and so appears to partake of the characters of both kinds.
In shape, to give a simple illustration, it resembles a spider, only
that the part below the head and thorax is larger in this creature
than in the spider. It has two thin red horns, and underneath these
horns two long eyes, not retreating inwards, nor turning sideways like
the eyes of the crab, but protruding straight out; and underneath
these eyes the mouth, and round about the mouth several hair-like
growths, and next after these two bifurcate legs or claws, whereby
it draws in objects towards itself, and two other legs on either side,
and a third small one. All below the thorax is soft, and when opened
in dissection is found to be sallow-coloured within. From the mouth
there runs a single passage right on to the stomach, but the passage
for the excretions is not discernible. The legs and the thorax are
hard, but not so hard as the legs and the thorax of the crab. It
does not adhere to its shell like the purple murex and the ceryx,
but can easily slip out of it. It is longer when found in the shell of
the stromboids than when found in the shell of the neritae.