帽狀幼體
Pilidium \Pi*lid"i*um\, n.; pl. {Pildia}. [NL., fr. Gr. ?, dim.
of ? a cap.] (Zo["o]l.)
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.