Of sea-nettles

there are two species, the lesser and more
edible, and the large hard ones, such as are found in the
neighbourhood of Chalcis. In winter time their flesh is firm, and
accordingly they are sought after as articles of food, but in summer
weather they are worthless, for they become thin and watery, and if
you catch at them they break at once into bits, and cannot be taken
off the rocks entire; and being oppressed by the heat they tend to
slip back into the crevices of the rocks.

So much for the external and the internal organs of molluscs,
crustaceans, and testaceans.