Longest colonial animal

The longest free-living colonial animal (i.e. excluding static coral reefs) is the memorably named long stringy stingy thingy (Apolemia uvaria). Its pelagic, free-floating colony resembles an extremely lengthy, thin piece of string bearing groups of long tentacles, acting as a predatory drift net, all of which is composed of numerous minute stinging polyp-shaped organisms known as zooids, together with some rather more specialized zooids serving variously as posterior swimming bells or an anterior gas float. Generally a colony of this species measures no more than 3 m (10 ft) long, but on 16 March 2020 a truly enormous spiral-shaped colony was encountered and filmed off the coast of Western Australia by the Ningaloo Canyons Expedition. Although it was impossible to measure the entire length of the colony on account of its shape, huge size and movements, its outer ring alone was estimated to be around 47 m (154 ft) and its total length up to 119 m (390 ft), which is far longer than not only any other siphonophore on record but also any other free-living life form of any kind known on Earth.

Belonging to the animal phylum Cnidaria, and therefore related to sea anemones, corals, jellyfishes and hydras, siphonophores are technically composite animals. For what looks like a single large multicellular organism is actually a permanent colony of smaller individual multicellular animals called zooids, each functioning as a specific unit or organ within that organism-resembling colony. Some zooids take the form of tentacles, others as reproductive organs, feeding organs, or buoyancy organs, and they cannot survive separate from the colony.

The most famous, and dangerous, siphonophore is the Portuguese man o' war (Physalia physalis), whose stinging tentacles have caused human deaths.