A
cephalopod (pronounced ) is any member of the
molluscan
class Cephalopoda (
Greek plural ,
kephalópoda; "head-feet"). These exclusively marine animals are characterized by
bilateral body symmetry, a prominent head, and a set of
arms or
tentacles (
muscular hydrostats) modified from the primitive molluscan foot. Fishermen sometimes call them
inkfish, referring to their common ability to squirt
ink. The study of cephalopods is a branch of
malacology known as
teuthology.