Ascidiacea

Ascidiacea is a class of marine tunicates whose adults are usually sessile filter feeders. Their saclike bodies draw water in through an oral siphon and expel it through an atrial siphon.

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Tunicate pharynx: A perforated branchial chamber that filters suspended particles from water in tunicates. Its internal slits strain food from water entering an ascidian's oral siphon.
Tunicates: Marine invertebrate chordates whose bodies are commonly enclosed in a tunic. Ascidiacea is one major group within this wider tunicate lineage.
Ciona intestinalis: A solitary sea squirt used extensively in studies of development, genetics, and chordate evolution. Its compact genome and transparent embryos make it a widely used ascidian model.
Solitary ascidians: Ascidians whose adult bodies live independently rather than forming an integrated colony. They contrast with colonial ascidians, despite sharing the same basic feeding architecture.
Oral siphon: An opening through which water enters the body of many aquatic animals. In ascidians, cilia and muscular action draw food-bearing water into the pharynx through this inlet.
Chordates: Animals that possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail at some life stage. Ascidians retain chordate traits most clearly in their free-swimming larvae.
Botryllus schlosseri: A colonial sea squirt used to study allorecognition, regeneration, and stem-cell biology. Its colonies undergo synchronized cycles of growth and regression that expose these processes.
Colonial ascidians: Ascidians whose zooids are connected in colonies and may share a common tunic or water outlet. Their coordinated colonies differ from the independent bodies of solitary species.
Atrial siphon: An opening that carries water out of the atrial cavity in tunicates. It releases water after it passes through the pharynx and atrial cavity.
Urochordata: A traditional name for tunicates, a chordate group that includes sea squirts, salps, and larvaceans. This classification places ascidians among the tunicates alongside other marine forms.