Evolution What the Fossils Say and Why it Matters

FIGURE 9.5. (A) The tunicates, or “sea squirts,” have adult body forms (right diagram) that look nothing like
chordates. However, the larvae (left diagram) are free-swimming tadpole-like creatures with tails and a
pharynx, that allowed them to escape their adult dead-end body form and evolve into higher chordates.
(After Romer 1959, redrawn by Carl Buell) (B) Photograph of the adult tunicate in feeding position. Courtesy
Wikimedia Commons)

Mouth

Brain Otocyst

Eye

Pharynx

Atrium

Gut

Atriopore

Nerve cord

Dorsal surfaceNotochord

Mouth

Gland

(? hypophysis)

Nerve

ganglion

Endostyle (cut

in sections)

Heart

Testis

Ovary

Stomach

Intestine

Anus

Atrium

PharynxPharynx

(A)

(B)