A cephalopod, belonging to the genus Loligo and related
   genera. There are many species. They have a sack of inklike fluid which
   they discharge from the siphon tube, when pursued or alarmed, in order
   to confuse their enemies. Their shell is a thin horny plate, within the
   flesh of the back, shaped very much like a quill pen. In America they
   are called squids. See Squid.