EVERYDAY SCIENCE

Detailed explanation-1: -1: Defining characteristics of chordates: In chordates, four common features appear at some point during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

Detailed explanation-2: -All chordates have a notochord at some stage in their lives, but in some (such as tunicates) the notochord is lost in the adult, whereas in others (such as the vertebrates) the notochord is present in the embryo, but in later stages is largely replaced and surrounded by the vertebrae, or backbones.

Detailed explanation-3: -"The four distinctive characteristics that, taken together, set chordates apart form all other phyla are the notochord; single, dorsal, tubular nerve cord; pharyngeal pouches; and postanal propulsive tail.

Detailed explanation-4: -Characteristics of Chordata. Animals in the phylum Chordata share four key features that appear at some stage during their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail ([link]). In some groups, some of these are present only during embryonic development.

Detailed explanation-5: -Answer and Explanation: Of the listed answers the one that is not one of the four chordate characteristics present in all chordates at some point during their development is the presence of mammary glands.