Annelida, or segmented worms, is a vast and diverse group of metazoans of over 20000 species that includes, amongst others, earthworms, leeches, echiurids, sipunculids and polychaetes. With over 300 species the polychaete family Cirratulidae is one of the most species-rich and common in benthic assemblages in a variety of habitats. However, it is also poorly known. The 24 species currently recorded in Norway are based on old and outdated descriptions. A vast majority of the specimens collected today have not and cannot be identified to species, as diagnostic characters are difficult to observe and often not well defined. Moreover, molecular studies indicate the presence of many undescribed and possibly cryptic species, up to 20 unknown species in the deep sea alone, which questions the accuracy of some previous species-level identification. Therefore, the diversity, distribution and species-ecosystem relationships within this common group are unknown despite large number of observations.

We have used the extensive collections accumulated over the years in the Norwegian natural history museums to assess the diversity of the group in Norwegian waters and map them at a fine scale over a very large geographic area, from the Skagerrak to Svalbard, and from coastal intertidal waters to the abyssal plains of the deep North-East Atlantic. More specifically, as the project used mostly museum collections, a wide area has been covered, comprising hundreds of stations. Oslofjord, Trondheimsfjord and the areas around Bergen and Tromsø are particularly well sampled. Other well-sampled areas include notably Sognefjord and Svalbard. Offshore areas include most of the slope of and parts of the continental shelf in the Norwegian Sea, part of the Barents Sea, parts of the deep sea around Jan Mayen, a vent side on the mid-Atlantic ridge and parts of the North Sea related to oil fields. In addition, specimens from outside Norwegian waters have been included for the process of species delimitation and identification. Moreover, many samples from around East Greenland, Iceland and Sweden have been examined to get a better understanding of species distributions in the North-East Atlantic and the Nordic Seas in particular. Accordingly, the sequenced specimens came from 250 different stations.

A total of 63 species have been found in Norwegian waters. These include four new records for Norway and one new species that we described from the hydrothermal vent field of Loki’s Castle. Most of the other 39 species are likely new to science, and several are in the process of being described. Two poorly known species have already been re-described and found to be widely distributed and among the dominant species in the deep sea. Over 8000 specimens have been examined in total and over 1000 records have been added to Artskart, including common, new and rare species. More records will be added as the museum collections are processed. Two papers presenting results obtained during this project have been published in the European Journal of Taxonomy, one on arctic cirratulids and the other one on the new species from Loki’s Castle vent field. Another paper presenting the results of molecular species delimitation in the family Cirratulidae has been published in Zoologica Scripta. A barcode library for the markers COI, 16S and 28S containing over 2000 sequences has been published and will serve as a framework and reference for future studies on annelid diversity and distribution in Norway, metabarcoding and environmental monitoring.