Ascidian Tadpole -

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:

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

A "gravity-sensor" that pulled him toward the safety of the dark seafloor. As he flicked his muscular tail, Pip felt

Pip did not eat. He had no mouth and no stomach. He was a living battery, powered only by the energy his mother had packed into his cells, and he knew—in the way a cluster of neurons can "know"—that time was running out. Pip did not eat

Pip was born into a world of endless blue, a shimmering 1 mm speck of potential drifting in the current. Unlike the stationary, colorful "adults" anchored to the reef below, Pip was a , built for a single, desperate mission: to find a home.

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

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