The reference type collection contains almost 800 different species (and as many types) on slides, corresponding to more than 3,000 microscope slides. This collection includes 8 different phyla (Annelida (300 specimens), Gastrotricha (28), Kinorhyncha (400), Loricifera (3), Nematoda (1300), Platyhelminthes (36), Rotifera (1200), Tardigrada (200)) and is accompanied by a large library on various groups living in the interstitial environment. It is the only properly structured collection in France in this field, and probably the third or fourth largest in the world (University of Ghent, Natural History Museum, Plymouth Marine Laboratory, Smithsonian Institution).

The meiofauna collection stems from the work carried out by the Free Worms Section, set up in 1968 as part of the former Worm Zoology Laboratory and then the Marine Invertebrate Biology Laboratory by J. Renaud-Mornant and N. Gourbault and G. Boucher. These laboratories are now closed, and the collection is housed at the Concarneau marine station.

As the general meiofauna collection is made up of several taxa, it includes several collections, those of free-living marine nematodes, Gastrotrichids, Kinorhynchids, Tardigrades, Turbellariids, Rotifers, Annelids, and various minor groups. The growth of the collection is mainly the result of collections made during oceanographic missions with an ecological theme, organised by the Muséum national d'Histoire naturelle or by other partner institutes such as the Ifremer.
 

The meiofauna collection at the Muséum national d'Histoire naturelle (MNHN) brings together a unique collection of specimens representing microscopic or very small organisms living in the interstices of sediments - mainly marine, but also living in freshwater. These living creatures, measuring between 40 micrometres and around 1 millimetre, play a key role in benthic ecosystems. They actively participate in the decomposition of organic matter and in biogeochemical cycles. They include an astonishing diversity of groups, often unknown to the general public, such as tardigrades, kinorhynchs, gastrotrichs and certain nematodes.

The study of meiofauna is relatively recent in the history of the natural sciences. It was only in the 20th century, with the improvement of microscopic sampling and observation techniques, that researchers began to take an in-depth interest. In the 1950s and 1960s, meiofauna emerged as a genuine field of study in marine biology and ecology, thanks to more efficient extraction methods and growing recognition of its ecological importance.
 

At the Muséum, the collection has been built up gradually over the decades, thanks in particular to the major oceanographic campaigns carried out in tropical and intertropical areas. Today, it stands out for its size and the taxonomic richness of its specimens, particularly in the groups of free-living nematodes and marine tardigrades.

However, the meiofauna collection faces a major obstacle: the lack of specialists capable of identifying and studying certain taxa, particularly kinorhynchs, tardigrades and loriciferans. This rarity gives the collection great scientific value for the study of marine biodiversity and the evolution of metazoans, but also makes it more complex to use.

To continue its development, the collection relies on a dynamic of international collaboration. The Muséum works closely with the world's few experts in these groups, involving them in field campaigns organised by the MNHN or other French institutes. These expeditions regularly bring in new specimens, often still unknown to science, and strengthen links with the scientific community.

Discreet but essential, the Muséum's meiofauna collection is a true reservoir of cryptic biodiversity. It supports taxonomic research and knowledge of aquatic ecosystems, by exploring what might be called the 'invisible frontiers' of biodiversity.

Cédric Hubas, Head of Collections
cedric.hubas [@] mnhn.fr
Tél. +33 1 40 79 57 45