1) Class 2) Class thaliacea 
The Thaliacea comprise a class of marine animals within the subphylum Tunicata. Unlike their benthic relatives the ascidians, thaliaceans are free-floating (pelagic) for their entire lifespan. The group includes species with complex life cycles with both solitary and colonial forms. ==Anatomy== The three orders of thaliaceans are filter feeders. P...
• (n. pl.) A division of Tunicata comprising the free-swimming species, such as Salpa and Doliolum.
(from the article `tunicate`) ...(or Larvacea)Adult small, pelagic, retaining larval notochord and tail; pharynx simple with two gill openings; no distinct atrium.Class ... The tunicates are divided into three classes: Ascidiacea (ascidians, or sea squirts), Appendicularia, and Thaliacea. Ascidians are largely benthic ... [2 related ...
Tha`li·a'ce·a noun plural [ New Latin See Thalia .] (Zoology) A division of Tunicata comprising the free-swimming species, such as Salpa and Doliolum. 
[n] - small class of free-swimming tunicates
class Thaliacea noun small class of free-swimming tunicates; sometimes classified as an order