Sea squirts

Ascidiacea

Ascidiacea, commonly referred to as ascidians or sea squirts, is a paraphyletic class within the subphylum Tunicata of sac-like marine invertebrate filter feeders. These organisms can be found distributed worldwide, primarily inhabiting shallow waters with salinities exceeding 2.5%. While certain members of the Thaliacea and Appendicularia subgroups, namely salps, doliolids, pyrosomes, and larvaceans, are capable of swimming like plankton, sea squirts adopt a sessile lifestyle upon reaching adulthood. They firmly attach themselves to substrates such as rocks and shells.

The class Ascidiacea encompasses approximately 2,300 distinct species, categorized into three main types: solitary ascidians, social ascidians that form clustered communities by attaching at their bases, and compound ascidians composed of numerous small individuals, known as zooids, which collectively form large colonies.

Sea squirts employ a feeding mechanism involving the intake of water through an oral siphon. The water enters the mouth and proceeds into the pharynx, flowing through mucus-coated gill slits, also referred to as pharyngeal stigmata. From there, the water is channeled into a water chamber called the atrium and is ultimately expelled through the atrial siphon.