Answer Key:
1) C 2) B 3) D 4) D 5) B 6) C 7) D 8) C 9) A 10) C 11) B 12) C
13. Chordates all have a notochord; a dorsal, hollow nerve cord; pharyngeal slits; and a muscular, post-anal
tail. The notochord, present in all chordate embryos, is a longitudinal, flexible rod located between the
digestive tube and the nerve cord. It is composed of large, fluid-filled cells encased in fairly stiff, fibrous
tissue. It provides skeletal support throughout most of the length of the animal. While the notochord
persists in the adult stage of some invertebrate chordates and primitive vertebrates, it remains only as a
remnant in vertebrates with a more complex, jointed skeleton. The dorsal, hollow nerve cord of a chordate
embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord. The nerve cord of
the chordate embryo develops into the central nervous system: the brain and spinal cord. The digestive tube
of chordates extends from the mouth to the anus. The region posterior to the mouth is the pharynx. In all
chordate embryos, a series of pouches separated by grooves forms along the sides of the pharynx. In most
chordates, these grooves (known as pharyngeal clefts) develop into pharyngeal gill slits that allow water
that enters the mouth to exit without continuing through the entire digestive tract. Most chordates have a
muscular tail extending posterior to the anus. In contrast, non-chordates have a digestive tract that extends
nearly the whole length of the body. The chordate tail contains skeletal elements and muscles. It provides
much of the propulsive force in many aquatic species.
14. The amphibians remained in damp habitats, burrowing in mud during droughts; some secreted foamy
protection for eggs laid on land. Reptiles developed scaly, waterproof skin, an amniotic egg that provided
an aquatic environment for the developing embryo, and behavioral adaptations to modulate changing
temperatures. All terrestrial groups are tetrapods, and they rely on using their limbs for locomotion on
land.
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