Source : Webster's Revised Unabridged Dictionary (1913)

Thaliacea \Tha`li*a"ce*a\, n. pl. [NL. See {Thalia}.] (Zo["o]l.)
   A division of Tunicata comprising the free-swimming species,
   such as Salpa and Doliolum.

{Vertebrata}, including Mammalia or Mammals, Aves or Birds,
Reptilia, Amphibia, Pisces or Fishes, Marsipobranchiata
(Craniota); and Leptocardia (Acrania). {Tunicata}, including the
{Thaliacea}, and {Ascidioidea} or Ascidians. {Articulata} or
{Annulosa}, including Insecta, Myriapoda, Malacapoda, Arachnida,
Pycnogonida, Merostomata, Crustacea (Arthropoda); and Annelida,
Gehyrea (Anarthropoda).

Source : WordNet®

Thaliacea
     n : small class of free-swimming tunicates; sometimes classified
         as an order [syn: {class Thaliacea}]