1. The urochordates are small marine organisms in which notochord is restricted to the tail of larva, therefore, named urochordates. 2. Some urochordates are sessile either as branching colonies or as individuals while many are found floating freely in water singly or in groups. 3. Size (0.25 to 250mm), shape and color variable. 4. Adult body degenerates, sac like, unsegmented, without paired appendages and usually with out tail. 5. They secrete a tough protective covering i.e., test or tunic, giving group the name Tunicata. Tunic is composed largely of tunicine, similar to cellulose. The tunic is often beautifully colored and usually transparent. 6. A terminal branchial aperture and a dorsal atrial aperture usually present. 7. Coelom is absent but body is surrounded by an atrial cavity or atrium, which open to exterior by atriopore. 8. Alimentary canal is complete. Pharynx is large, with endostyle and two to several pairs of gill slits. 9. The adults are highly developed filter feeders. 10. Respiration is through test and gill slits. 11. Open circulatory system is present. 12. Excretion is by neural glands. 13. Mostly hermaphrodites, External and cross fertilization present.
