Bicellum brasieri is a fossil holozoan.

[1] It is one billion years old and could be the oldest example of complex multicellularity in the evolutionary lineage leading to the animals,[2][3] and has been described as bridging "the gap between the very first living creatures — single-celled organisms — and more complex multicellular life.

"[4] It was discovered in 2021, and is posthumously named after the late Martin Brasier, a paleontologist who was a co-author of the paper that first described it.

[5] Bicellum was found in sediments from the Diabaig Formation in Loch Torridon, Scotland.

The Diabaig Formation, considered to represent an ancient lake deposit,[6] was already known to preserve the first non-marine eukaryotes.