gymnocopa

from The Collaborative International Dictionary of English v.0.48

Gymnocopa \Gym`no*co"pa\ (j[i^]m`n[-o]*k[=o]"p[.a]), n. pl.
   [NL., fr. Gr. gymno`s naked + kw`ph an oar.] (Zool.)
   A group of transparent, free-swimming Annelida, having
   set[ae] only in the cephalic appendages.
   [1913 Webster]