The marine biodiversity of Europe is generally considered well known comparison to other regions, especially of the global South. However, also in European waters, some habitats and regions have been scarcely studied and many species could remain to be discovered and described. This has been shown, for example, by numerous studies based on DNA sequence data on various groups of annelids including some studies from our own group (see for example this blog post). In a recent paper with Mael as the lead author published in Zoologica Scripta, we investigated the annelid family Cirratulidae in this respect.

Species of Cirratulidae can be found in all oceans and are common in soft sediments as well as hard substrates. They are typically characterized by the arrangement of their long, filamentous branchiae along the first body segments. In addition, they have feeding tentacles in the form of either two thick grooved palps or as two groups of long and thin filaments. However, in some species, feeding tentacles are absent.

Cirratulidae as a group comprises at least 397 species in 16 genera worldwide and 58 in European waters, also in 16 genera. 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 our study was to assess the species diversity of Cirratulidae in European waters. We used therefore already available samples collected at different events and stored at different museums. The samples ranged from the Arctic Ocean North of Svalbard along the European Atlantic coast to the western Mediterranean Sea. The depth distribution was also quite large ranging from the intertidal zone down to 2600m deep. In total, over 400 sampling sites included in the study.

To understand the species boundaries and distribution, we used molecular data instead of morphological data. To this end, we included 2120 sequences from two mitochondrial (COI and 16S rRNA) and one nuclear marker (28S rRNA) for 1098 specimens in our analyses. Most of the sequences were generated by ourselves, in specific 65%, specifically for this study. We performed different relevant species delimitation analyses to determine the true number of cirratulid species occurring in European waters. As a result, 125–129 species were identified. While the assignment to morphological species is still ongoing as this requires time and availability of type material, we still could estimate that between 83 to 96 of the species represent putative new species to science.