Characteristics:
Sea squirts are sessile tunicates, i.e. they all have a life stage attached to the bottom or some other surface. There are more than 2300 marine species, all over the world. Some are colonial or at least tends to clump together, others live a life in solitary. They are filter feeders, extracting food from the water. They are usually found in shallow waters where the salinity is more than 2.5 %
Taxonomy:
The sea squirts are separated in three orders, all presented here:
- Aplousobranchia are colonial sea squirts.
- Phlebobranchia includes both colonial and solitary species. They have a longitudinal vessel, like a blood vessel, in the stomach-like organ, called the pharyngeal basket.
- Stolidobranchia includes both colonial and solitary species. Their pharyngeal basket is folded.