The sponge breeds parasites,

worms, and other creatures, on
which, if they be detached, the rock-fishes prey, as they prey also on
the remaining stumps of the sponge; but, if the sponge be broken
off, it grows again from the remaining stump and the place is soon
as well covered as before.

The largest of all sponges are the loose-textured ones, and
these are peculiarly abundant on the coast of Lycia. The softest are
the close-textured sponges; for, by the way, the so-called sponges
of Achilles are harder than these. As a general rule, sponges that are
found in deep calm waters are the softest; for usually windy and
stormy weather has a tendency to harden them (as it has to harden
all similar growing things), and to arrest their growth. And this
accounts for the fact that the sponges found in the Hellespont are
rough and close-textured; and, as a general rule, sponges found beyond
or inside Cape Malea are, respectively, comparatively soft or
comparatively hard. But, by the way, the habitat of the sponge
should not be too sheltered and warm, for it has a tendency to
decay, like all similar vegetable-like growths. And this accounts
for the fact that the sponge is at its best when found in deep water
close to shore; for owing to the depth of the water they enjoy shelter
alike from stormy winds and from excessive heat.