of fish and animal species with backbones,
from snails just a millimeter across to giant
clams and squids.
The secret to the molluscs’ success — and
their strangeness — is their adaptable body
plan. It includes three major parts: a muscular
“foot” for moving; an intricate assembly that
includes the circulatory, digestive, and sexual
organs; and enveloping this assembly, a
versatile sheet-like “mantle” that takes on
such jobs as secreting materials for a shell,
supporting eyes and small tentacles that detect
food or danger, and contracting and relaxing
to control water flow into the interior. The
molluscan shellfish that we eat have
combined these parts in very different ways.
Abalones, the most primitive, have one
cup-like shell for protection, and a
massive, tough muscular foot for moving
along and clinging to the seaweed on
which their rasping mouths feed.
Clams are enclosed in two shells, and