LAUSR

Simple Summary Diopatra is a genus of marine annelids common in shallow, tropical or subtropical waters. They can occur in great densities and are important ecosystem engineers due to their robust tubes stabilizing sediments. Their large size and striking spiraled branchiae led these worms to be well studied by pioneer taxonomists, and the genus itself was early on well defined. Despite this, delimiting species within Diopatra has been difficult due to overlapping morphological characters. In this study we aimed to assess the species diversity of Diopatra in West African waters and examine the relationship within the genus using molecular tools. We discovered 17 new species, some of which could not be distinguished from closely related species using only morphology. We also uncovered five well supported clades within Diopatra, four of them reinforced by morphological synapomorphies. Extinction rates are increasing in the Anthropocene, and the entire field of conservation biology is directed towards preserving species. A problem facing the field is that it impossible to meaningfully protect what is not known, and there is a fear that species are going extinct before they are discovered. Studies such as this, mapping unknown biodiversity, is imperative in the effort to protect species and biological communities. Abstract Diopatra Audouin & Milne-Edwards, 1833 is a species rich genus that is common in tropical and subtropical regions. The genus is readily identified by its striking, spiral branchiae, but species identification has historically been challenging due to a high variation in diagnostic characters used. This study aims to reconstruct the phylogeny of Diopatra with molecular markers and assess the species diversity of West African Diopatra with the species delimitation programs bPTP and BPP. Specimens were collected from Morocco to Angola, and the markers COI, 16S and 28S were sequenced from 76 specimens. The constructed phylogeny retrieved Diopatra as monophyletic, as well as five well supported clades within the genus. All clades were defined by morphological characters, some of which have previously not been considered to have high phylogenetic or taxonomical value. Species delimitation analyses recovered 17 new species, several of which were not readily identified morphologically. One species complex comprising between one and 12 species was left unresolved due to incongruence between the species delimitation methods and challenging morphology. Our results indicate that the diversity of Diopatra is significantly underestimated, where this regional study near to doubled the number ofknown species from the East Atlantic.