Pyrosome

A pyrosome is a floating hollow tube made of thousands of tiny animals joined together into one colony. These tiny animals are called zooids, and each is only a few millimetres long. The name Pyrosoma means 'fire body' in Greek, because the colony glows in the dark.

Pyrosomes belong to a group called tunicates and live in the upper layers of warm open seas all over the world. There are three genera and eight species. A colony is usually under half a metre long. They are often nicknamed sea pickles because of their gelatinous, bumpy tube shape. Pyrosomes are hermaphrodites, meaning each animal has both male and female parts.

One animal made of many

Each tiny zooid opens to the outside and the inside of the tube. It pulls in seawater and filters out microscopic plant cells to eat, then pushes the water into the hollow centre. The walls of the tube are thick jelly, 0.2 to 2.0 centimetres. The beating hairs of all the zooids work together and slowly push the whole colony along, like jet propulsion.

Glow and blooms

Pyrosomes flash a pale blue-green light that can be seen from tens of metres away. Sailors have sometimes seen calm, dark seas full of glowing pyrosomes. They are close relatives of salps. Sometimes they form huge blooms that change the food web in the open sea, and when dead colonies sink to the sea floor they become food for other animals and carry carbon down.

On the globe

The model shows a pyrosome as a glowing tube drifting in the open sea. Look for the pale blue-green glow.