On the genus Lagenopolycysitis Artois and Schockaert, 2000 (Platyhelminthes, Kalyptorhynchia, Polycystididae), with the description of six new species

Abstract

Meiofauna, broadly defined as those organisms able to pass through a 1-mm sieve but retained by a 45-μm mesh, comprise a highly diverse assemblage of invertebrates. Despite their high diversity and abundance, their ubiquitous presence across the globe, and their important role in ocean health and ecosystem functioning, these animals are frequently overlooked in biodiversity assessments. A prime example of such an understudied group is Rhabdocoela Ehrenberg, 1831, a highly speciose and ecologically diverse group of flatworms with over 1500 species found worldwide. As top predators, these microturbellarians are assumed to play a key role in meiofaunal ecosystems, yet many species remain undescribed to date. This study focuses on Lagenopolycystis, a rhabdocoel genus originally described in 1965, which currently includes only two described species. By combining results from over 30 years of marine sampling campaigns across Europe and Eastern Africa conducted by our research group, we now present an updated description of the genus, followed by a redescription of the type species Lagenopolycystis peresi Brunet, 1965, and L. mandelai Willems & Artois, 2017. Additionally, we describe a total of six species new to science. The new species are mainly distinguished from each other and other representatives of Lagenopolycystis by the organization of their reproductive systems. Comments on the genus' distribution and phylogeny are provided. Our findings contribute to our understanding of microturbellarian diversity, and underscore the need for continued exploration and description of meiofaunal species by future researchers.