Section 2

Invertebrate Chordates

• Chordates have a notochord, a stiff but flexible rod that runs the length of the body. In one group of chordates, the vertebrates, the notochord is largely replaced by the vertebral column, or backbone.

• Other common characteristics of chordates are a dorsal nerve cord, pharyngeal pouches, and a postanal tail. These characteristics are not present at all life stages in all chordates.

• Like echinoderms, chordates are deuterostomes, which suggests that echinoderms and chordates evolved from a common ancestor.

• Lancelets are animals in the subphylum Cephalochordata. These blade-shaped animals live partially buried in the sand, but they can swim from place to place. They retain all of the major chordate characteristics throughout their life.

• Tunicates are animals in the subphylum Urochordata. Tunicate larvae have all of the major chordate characteristics, but they lose most of them when they develop into adults. Most tunicate adults are sessile.

Vocabulary atriopore (p. 770)

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