Of those

swimming creatures that appear to have feet, as is the
case with the molluscs, these creatures swim by the aid of their
feet and their fins as well, and they swim most rapidly backwards in
the direction of the trunk, as is the case with the cuttle-fish or
sepia and the calamary; and, by the way, neither of these latter can
walk as the poulpe or octopus can.

The hard-skinned or crustaceous animals, like the crawfish,
swim by the instrumentality of their tail-parts; and they swim most
rapidly tail foremost, by the aid of the fins developed upon that
member. The newt swims by means of its feet and tail; and its tail
resembles that of the sheatfish, to compare little with great.