Sea squirt

This soft vase is one of our closest cousins without a backbone. Its wider family, the sea squirts, is the sister group to all animals with backbones, including us. Each one starts life as a tiny tadpole only a few millimetres long. It has a tail, a simple rod called the notochord that is the forerunner of our backbone, and a primitive nervous system with a light-sensing eyespot and a gravity sensor to steer by.

The tadpole never feeds. Within hours to a day or two it must glue its head to a rock, shell or jetty piling. Then it rebuilds itself. It absorbs its own tail and most of its swimming nervous system, keeping only a small cluster of nerves for adult life.

The adult stays fixed in one spot as a filter feeder. Often about as long as a hand, its see-through outer coat is usually pale yellow-green and shows the orange or yellow gut loop and striped food basket inside. It draws water in through one chimney-like siphon, traps plankton and drifting scraps in mucus, then pushes the water out of a second siphon. Touch one and it squirts — that startled squeeze gave sea squirts their name.