Tadpole | Ascidian

A "light-eye" that told him to swim away from the bright surface where predators lurked.

As he flicked his muscular tail, Pip felt the power of his , a flexible rod that made him a relative of the great whales and humans. His tiny brain, a cluster of only 170 neurons, hummed with data from two specialized organs: ascidian tadpole

The is a tiny, free-swimming larva that represents a fleeting moment of mobility in the life of a sea squirt. Though it measures only about 1 mm and lives for just a few days, it possesses complex features—like a primitive spinal cord (notochord) and a simple brain—that it will eventually digest to become a stationary adult. The Great Descent of Pip A "light-eye" that told him to swim away

A "gravity-sensor" that pulled him toward the safety of the dark seafloor. Though it measures only about 1 mm and

After twelve hours of frantic swimming, Pip's brushed against a rough, granite ledge. His light-sensitive eye confirmed the spot was shaded, and his gravity sensor confirmed he had reached the bottom. With a final, decisive surge, he pressed his head against the stone and triggered the chemical "glue" that would bind him for life. the swimming larva and its metamorphosis - Nature