Pilidium
Pronunciation : Pi*lid"i*um
Part of Speech : n.;
Etymology : [NL., fr. Gr. (Zo?l.)
Definition : Defn: The free-swimming, hat-shaped larva of certain nemertean worms. It has no resemblance to its parent, and the young worm develops in its interior.
pl. Pildia.
Source : Webster's Unabridged Dictionary, 1913