Species diversity and taxonomy of Dakuidae (Acoela)

Acoela are a group of microscopic worms that remains poorly known despite their high abundance and world-wide distribution. Within Acoela, the family Dakuidae has undergone several taxonomic changes in recent decades, yet its internal phylogeny remains unclear. Herein, we describe seven new species of Dakuidae from Croatia, Germany, Italy, Panama, and Sweden: Philactinoposthia brunopunctata sp. nov., Philactinoposthia centrofusca sp. nov., Philactinoposthia raikovae sp. nov., Philactinoposthia gracilia sp. nov., Philactinoposthia parvipenis sp. nov., Philocelis leasae sp. nov. and Philocelis dunensis sp. nov. Mitochondrial (COI) and nuclear (18 S, 28 S) sequences were used to assess the phylogenetic relationships within the family, supporting the presence of two sister groups: the first comprising species of the genus Philocelis along with Philactinoposthia saliens , Philactinoposthia rhammifera and Daku woorimensis , and the second consisting of other species of the genus Philactinoposthia . P. saliens and P. rhammifera are transferred from Philactinoposthia to Philocelis . The genus Daku is synonymised with Philocelis. Finally, we assessed the diagnostic relevance of the morphological characters traditionally used in the taxonomy of Dakuidae, proposing emended diagnoses for the genera Philocelis and Philactinoposthia .