SRA

Deep-sea floors represent one of the largest and most complex ecosystems on Earth but remain essentially unexplored. Th vastness and remoteness of this ecosystem make deep-sea sam pling dif?cult, hampering traditional taxonomic observations an diversity assessment. This is particularly true in the case of th deep-sea meiofauna, which largely comprises small-sized, fragile and dif?cult-to-identify metazoans and protists. Here, we intro duce an ultra-deep sequencing-based metagenetic approach to ex amine the richness of benthic foraminifera, a principal componen of deep-sea meiofauna. We used Illumina sequencing technolog to assess foraminiferal richness in 31 unsieved deep-sea sedimen samples from ?ve distinct oceanic regions. We sequenced an ex tremely short fragment (36 bases) of the small subunit ribosoma DNA hypervariable region 37f,which has been shown to accuratel distinguish foraminiferal species. In total, we obtained 495,97 unique sequences that were grouped into 1,643 operational taxo nomic units, of which about half (841) could be reliably assigned t foraminifera. The vast majority of the operational taxonomic unit (nearly 90%) were either assigned to early (ancient) lineages o soft-walled, single-chambered (monothalamous) foraminifera o remained undetermined and yet possibly belong to unknown earl lineages. Contrasting with the classical view of multichambere taxa dominating foraminiferal assemblages, our work re?ects a unexpected diversity of monothalamous lineages that are as ye unknown using conventional micropaleontological observations Although we can only speculate about their morphology, the im mense richness of deep-sea phylotypes revealed by this study sug gests that ultra-deep sequencing can improve understanding o deep-sea benthic diversity considered until now as unknowabl based on a traditional taxonomic approach.