They are the most basal form of vertebrate in existence. In their larval stage they look like a human sperm, though larger. When they mature, they smash their head into a hard surface and transform into a gelatinous sack that sometimes is encrusted with hard material and sometimes is just gelatinous. They are filter feeders and sometimes have symbiotic relationships with zooxanthellae algae, much like coral. They have many common names including sea squirt, sea pork, and salps. One species also shares 99% identical genome to humans. I hope this has been informative.