The sea tulip is covered in lumps and bumps, giving it a kind of warty appearance.
It comes in a variety of colours such as orange, purple, yellow, or pink. These bright colours aren’t the work of the sea tulip but are from an encrusting sponge, halisarca australiensis, which covers its surface.
Sea tulips live in coastal waters in depths down to 80 metres. Despite what most people think, they are animals, not plants. The sea tulip is sessile (unable to move around) and so waits for the currents to bring food to it. Like all sea squirts, the sea tulip is a filter feeder pumping water in and out of its siphons, and extracting the plankton.
The relationship between the sea tulip and the encrusting sponge enable the sea tulip to gain protection from predators by using the sponge’s defenses while the sponge benefits by having a surface on which to grow. Many sponges contain compounds to deter predators.