Abstract
The cumulative number of parasite species known to science keeps increasing steadily year after year, suggesting we are far from the end of our inventory of extant parasite biodiversity. However, what about higher taxa such as genera or families: are their known numbers also still rising? Finding new genera or families represents the discovery of clades with greater evolutionary uniqueness than the discovery of new species belonging to already known lineages. We surveyed the taxonomic literature between 2010 and 2025 to quantify patterns in the discovery of new helminth genera and families. Few new families were proposed during the study period, however 271 new genera were established, with 80% of them being 'true' new genera, i.e. previously unknown lineages based entirely on the discovery of new specimens. Whereas we might expect that the more genera one has already found, the harder it could be to find new ones, we instead found a positive relationship between the number of new genera found per higher taxon and the currently known species richness of that taxon. This supports a sampling hypothesis whereby species-rich taxa like Trematoda are also the ones likely to yield more new genera. Indeed, the cumulative number of new trematode genera found in the 2010-2025 period has increased linearly, suggesting many more genera await discovery in this taxon as well as in Nematoda, Monopisthocotylea and Polyopisthocotylea. In contrast, an asymptote has been reached in Acanthocephala and Cestoda, indicating the final list of genera is at hand in those taxa. Our findings suggest that the quest to document parasite biodiversity is far from complete as we still lack knowledge of many phylogenetically distinct helminths characterised by morphologies that do not fit within currently known genera.