The main characteristic of the annelid is the pattern of repeated segments. These pentaradial animals are characterized by spiny coverings, pedicellariae, and water vascular systems. All chordates have a notochord at some time in development, a dorsal nerve cord, a post-anal tail, and pharyngeal gill slits. The tunicates have a nonliving covering which contains cellulose. The vertebrates have a vertebral column.
Mammals have milk-secreting mammary glands and hairy bodies.
Subclassification is based upon the ways mothers carry and bear their young. The McGraw-Hill Companies. Any use is subject to the Terms of Use and Privacy Policy .