Australia's Biodiversity

Loriciferans (Phylum Loricifera)

Loriciferans are so rare, so tiny, and so recently discovered that they have yet to receive a common name. Unlike the vast majority of animal phyla, which were formally named in the eighteenth and nineteenth centuries, loriciferans were discovered and named in 1983.

Around 90 species have been described since. As they are so recently discovered, little is known about them, and less is known about the four Australian species discovered to date.

The loriciferan Nanaloricus mysticus. The animal is about 0.25 mm long.

Loriciferans have a hard, corset-shaped shell called a lorica, inside which is a head with an introvert surrounded by rings of elongate spines called scalids. They are tiny (mostly less than half a millimetre long), and are invisible to the naked eye. They live between grains of sand and gravel on ocean floors, where they are understood to eat bacteria, microalgae, and organic particles too small for most other organisms.

Loriciferans are typically found in shallow waters, but in rare cases may be found 8000 m beneath the surface. In some parts of the world they are numerous in highly saline, sulphur-rich water that is entirely lacking in oxygen. The loriciferans that live in these unusual environments have specialised mitochondria called hydrogenosomes that can produce energy without needing oxygen. They are the only-known multicellular animals to have hydrogenosomes instead of mitochondria.

Diagrammatic representation of the loriciferan Pliciloricus enigmatus. Image by Carolyn Gast, National Museum of Natural History - http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/oceanography_recently_revealed2.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=530608

Despite their very recent discovery, the discovery of a rare and beautifully preserved loriciferan from Cambrian mudstones in Canada shows that loriciferans are an ancient group that have scarecely changed their body plan for 500 million years.

The loriciferan Nanaloricus mysticus. The animal is about 0.25 mm long.

The only loriciferans known from Australia were discovered in submerged sea caves, Jim's Cave and Fish Rock Cave, off NSW. The fact that Australian loriciferans are only found in marine caves suggests these may be small remnant populations of ancient deep-sea groups.

Interestingly, one juvenile Australian loriciferan had conspicuously coloured light-sensing organs in its head. Prior to this discovery, biologists assumed that loriciferans lacked light-sensing organs altogether, possibly because these sensitive organs were damaged during the preparation of samples for analysis (remember microscopes are necessary to see even the largest loriciferans). Thanks to this Australian discovery, however, biologists now know to look for eyes in loriciferans. The question of why an Australian loriciferan that lives in caves, where there is no light, needs light-sensing organs remains open.

Given that Australian loriciferans remain understudied, more species are likely to be found around our coastlines.

Thanks to Robin Hare from the University of Western Australia for help preparing this profile.