English: Acidians; Sea squirts.
Genera: 2300 species.
Region: worldwide.
Habitat: shallow water, with salinities over 2.5%.
ZoologyAscidiacea are sac-like marine invertebrate filter feeders; they are sessile after their larval phase, firmly attached to rocks and shells; three main types: solitary ascidians, social ascidians that form clumped communities by attaching at their bases, and compound ascidians consisting of many small individuals or zooids, forming colonies up to several meters in diameter.
Form: they have a tough outer "tunic" made of a polysaccharide.
Food: they feed by taking in water through a tube, the oral siphon; water enters the mouth and pharynx, flows through mucus-covered gill slits, also called pharyngeal stigmata, into a water chamber called the atrium, then exits through the atrial siphon.