"In an era of global changes, the understanding of the biodiversity became a major issue of science. While some particular groups such as fishes, crustaceans or molluscs are relatively well known, most of the small sized metazoan taxa, which often have few morphological distinctive characters, remain largely undescribed. The difficulties encountered to identify those organisms resulted in a dramatic lack of knowledge on these taxa, often qualified as minor taxa. Most of those organisms are present in the meiobenthos and their ecological importance recently became clear. Meiobenthos also hosts some evolutionary important albeit enigmatic phyla which diversity is almost unknown. In this project, modern molecular methods such as DNA barcoding coupled with environmental massive sequencing technologies will be used to investigate the diversity of the meiobenthos. The main objective of this study will be the development of new molecular tools to explore marine meiofaunal biodiversity. These tools will be tested on a case study testing the hypothesis of the cosmopolitism of deep sea meiobenthos. To achieve these objectives, short environmental DNA fragments obtained from multiple samples by massive sequencing will be analysed following a DNA-barcoding approach. Specific probes developed for the selected poorly known taxonomic groups will be then used for investigating their richness in sediment samples. New taxa will be described in collaboration with specialists. The project will provide the first genetic insight in the global metazoan diversity of the deep sea meiobenthos. It will contribute to assess the ecological importance and geographical distribution of small-sized marine animals. The probability to discover new taxonomic groups might lead to significant advances in the understanding of metazoan evolution. Moreover, this project will provide an accessible tool to identify “minor taxa” that can be further used by non specialists."