Thecosomata

from The Collaborative International Dictionary of English v.0.48

Thecosomata \The`co*so"ma*ta\, n. pl. [NL. See {Theca}, and
   {Soma}.] (Zool.)
   An order of Pteropoda comprising those species which have a
   shell. See {Pteropoda}. -- {The`co*so"ma*tous}, a.
   [1913 Webster]