Largest thaliacean

The largest thaliacean is the giant fire salp Pyrostremma spinosum, a pelagic species of pyrosome, which has been encountered (and sometimes filmed) in open water off Tasmania, Australia and also New Zealand. Technically, it is a "super-organism" rather than a single organism, because it is actually a colony composed of thousands of tiny individual filter-feeding organisms known as zooids, but these never exist independently, only together, yielding an extremely long, fragile, hollow, tubular, free-floating "super-organism", which can measure 20–30 m long and over 1 m wide, tapers from the open end of the tube to the other, closed end, and is bioluminescent. If touched, it is said to feel like a flimsy feather boa.

Together with larvaceans, sea-squirts and lancelets, thaliaceans are the closest living relatives of chordates, the phylum that includes vertebrates – animals with backbones. Once, a penguin was discovered dead inside a P. spinosum super-organism, leading to lurid media claims that the latter had actively swallowed the penguin and killed it. In reality, however, it is merely a passive, filter-feeding, tapering tube-shaped colony, incapable of actively engulfing anything. Consequently, either the penguin swam inside the colony's tube and drowned while trying to swim back out again, or it was already dead and its body had simply drifted inside the tapering tube and lodged there.

A spectacular video featuring one gigantic tubicolous colony of the giant fire salp (plus various other, smaller thaliacean species), as filmed and released publicly in 2013 by Eaglehawk Dive Centre in Australia, including Michael Baron, can be viewed online at: https://www.youtube.com/watch?time_continue=3&v=5EQGA_4BZ5s