Taxonomy:

Polycarpa aurata (Quoy & Gaimard, 1834)

Kingdom: Animalia 

Phylum: Chordata

Subphylum: Urochordata

Class: Ascidiacea

Order: Stolidobranchia

Family: Styelidae

Genus: Polycarpa 

Species: aurata

Tunicates such as this Polycarpa aurata specimen are true filter feeders, which are able to filter hundreds of liters of water per day and remove over 95% of its bacteria. Water is pumped through the branchial siphon, and eventually out of the atrial siphon. Inside the animal, bacteria and phytoplankton are filtered from the water, which are trapped by the mucous layer lining the branchial basket of the tunicate. These animals are able to contract or deflate by pumping water out of their body cavities. During this process, the branchial siphon is closed off. They  inflate by opening up their branchial siphon, and closing off the atrial siphon. For a detailed article about these unique creatures, see the article of Dr. Shimek in Advanced Aquarist's Online Magazine.

Author: 

Tim Wijgerde

References:

World Register of Marine Species (WoRMS)

Tim Wijgerde, pers. obs.