Molecular Investigation of the Diversity of Cirratulidae (Annelida) Doubles the Number of Known Species in European Waters

ABSTRACT Cirratulidae is a group of common marine benthic annelids with about 397 nominal species described worldwide, 58 of which are reported in European waters. Due to the general morphological homogeneity among species from several genera, this group is considered difficult to identify to species level, has a complex taxonomical and nomenclatural history and is largely understudied. The aim of this study was to assess the species diversity of Cirratulidae in European waters. Available samples ranged from the Arctic Ocean North of Svalbard, along the European Atlantic coast and the western Mediterranean Sea, and from the intertidal zone down to 2600 m deep, with over 400 sampling sites included. We included 2120 partial sequences from two mitochondrial (COI and 16S rRNA) and one nuclear marker (28S rRNA) from 1098 specimens in analyses, 65% of which were newly produced for this study. We performed relevant distance and tree‐based species delimitation analyses (ASAP, PTP, mPTP and GMYC). As a result, 125–129 lineages compatible with the evolutionary definition of species were identified, out of which 83 to 96 lineages represent putative new species to science. This study represents the most inclusive phylogenetic analyses to date. Multitentaculate Cirratulidae is retrieved as a monophyletic group with the inclusion of Chaetocirratulus. The genera Cirratulus , Chaetocirratulus , Caulleriella , Tharyx and Raricirrus are recovered monophyletic. The genus Chaetozone is recovered paraphyletic with Caulleriella nested within it, and the status of the genera Aphelochaeta and Kirkegaardia is unresolved.