The Collaborative International Dictionary of English v.0.48:

Tethyodea \Te`thy*o"de*a\, n. pl. [NL., fr. Tethys + Gr. e'i^dos
   form.] (Zool.)
   A division of Tunicata including the common attached
   ascidians, both simple and compound. Called also
   Tethioidea.
   [1913 Webster]