plan·u·la 
(plănyə-lə)
(plănyə-lə)n. pl. plan·u·lae (-lē′)
The flat, free-swimming, ciliated larva of a cnidarian.
[New Latin plānula, from Latin, feminine diminutive of plānus, flat (from its shape); see pelə-2 in the Appendix of Indo-European roots.]
planu·lar, planu·late′ (-lāt′) adj.