The Lightbulb Sea Squirt is a transparent-looking sea creature that is almost tube-like in appearance. It lives in a group called a colony and can be found around most of the coasts of England in clear waters as deep as twenty to fifty metres. It attaches itself onto vertical rock faces, shells and seaweed. It has the name 'Lightbulb' because it seems to glow like a lightbulb. It also has yellow or white lines running vertically down its transparent body and you can see its internal organs, just like you can see the inside of a lightbulb.

The Lightbulb Sea Squirt colony is made up of lots of individual ‘zooids’. A zooid is a living organism that takes the form of a ‘U’ shaped tube. It has a tough transparent gelatinous tunic around it for protection. Each zooid has two openings. One of the openings takes water in, while the other opening squirts water out, but if the Lightbulb Sea Squirt feels threatened or if it is disturbed, it can contract its body and squirt water out of both tubes. A colony of zooids can grow about two centimetres tall and about fifteen centimetres in diameter.

The larvae of the Lightbulb Sea Squirt are often called ‘tadpoles’ and when they first hatch out of the eggs they swim upwards towards the light. Eventually they settle back into the darkness of the seabed where they develop into adult Lightbulb Sea Squirts.