- Exclusively marine and cosmopolitan, found in all seas and at all depths.
- Mostly sedentary (fixed), some palagic or free swiming.
- Simple (solitary), aggregated in groups or composite (colonial).
- Size (0.25 to 250 mm), shape and colour variable.
- Adult body degenerate, sac-like, unsegmented, without paired appendages and usually without tail.
- Body covered by a protective tunic or test composed largely of tunicine similar to cellulose, hence the name Tunicata.
- A terminal branchial aperture and a dorsal atrial aperture usually present.
- Coelom absent. Instead, an ectoderm-lined atrial cavity present which opens to outside through atrial apertures.
- Notochord present only in larval tail, hence the name Urochordata.