Description of a new species of gastrotrich (Gastrotricha: Macrodasyida) from the North Brazil Shelf with insights on the phylogeny and historical biogeography of Thaumastodermatidae

A new species of Pseudostomella is described from a sand beach of the North Brazil Shelf ecoregion, Piauí State, using differential interference contrast microscopy, scanning and transmission electron microscopy, and confocal microscopy. The new species can be distinguished from its congeners by the higher number of cirrata tubes, the size of the pentancres, and the bipartite caudal organ. A phylogenetic reconstruction based on morphological data was carried out and the new species fell into a clade including P. squamalongispinosa and P. dolichopoda, two other species originally described from the Brazilian coast. Historical biogeography of the thaumastodermatids suggests a diversification of two distinct lineages after the breakup of Pangea, as the biogeographical patterns of these gastrotrichs that inhabit the worldwide coasts showed affinities, respectively, with Gondwana and Laurasia biogeographical provinces.