Assessing the diversity and distribution ofCephalothrixspecies (Nemertea: Palaeonemertea) in European waters by comparing different species delimitation methods

Abstract

Soft‐bodied marine taxa, like ribbon worms (Nemertea), often lack clear diagnostic morphological characters impeding traditional species delimitation. Therefore, recent studies concentrated on molecular genetic methods to solve taxonomic issues. Different delimitation methods were employed to explore species boundaries and the presence of cryptic species. However, the performance of the different delimitation methods needs to be tested. A particularly promising nemertean genus in this regard is the palaeonemertean genus Cephalothrix that is commonly found in European waters. In order to gain information on the number and distribution of European cephalotrichids and to test different tree‐based and non‐tree‐based delimitation methods, we analyzed a dataset comprising the barcoding region of the mitochondrial cytochrome c oxidase subunit I (COI) of 215 European Cephalothrix specimens, of which 78 were collected for this study. Our results show the presence of 12–13 European lineages of which several can be assigned to known European species. Analyzing a second dataset comprising 74 additional sequences from the Pacific and the Atlantic Oceans helped identify some of the unassigned European specimens. One resulting clade seems to represent a non‐native introduced Cephalothrix species, while another has never been recorded from Europe before. In our analysis, especially the tree‐based methods and the phylogenetic analysis proved to be a useful tool when delimiting species. It remains unclear whether the different identified clades result from cryptic speciation or from a high genetic variability of the COI gene.

Resolving a 200-year-old taxonomic conundrum: neotype designation for Cephalothrix linearis (Nemertea: Palaeonemertea) based on a topotype from Bergen, Norway

“…In the public nucleotide databases, however, the accession numbers KP697715-KP69771521 and KU840290 are still anchored to the name 'Cephalothrix linearis' as of March 2019. Based on these sequences, the associated name Cephalothrix linearis has been used 'improperly'-in the light of the present work, though-in Sagorny et al (2019). Although Sagorny et al (2019) sampled Cephalothrix specimens in Bergen (Norway), all they obtained in this place turned out to be either C. filiformis (MH681957, MH681958, MH681960) or C. rufifrons (MH681896).…”

“…Indeed, C. linearis s.str. was not included in the 78 Cephalothrix specimens that Sagorny et al (2019) collected at six localities in Europe: Norway (Bergen), Sweden (Kristineberg), France (Roscoff, Concarneau), Italy (Giglio), and Spain (Blanes), suggesting the rarity of the species.…”

Diversity of interstitial nemerteans of the genus Ototyphlonemertes (Nemertea: Monostilifera: Ototyphlonemertidae) in the South China Sea, with a comment on the distribution pattern of the genus

“…As commented by Sundberg et al (2016a), molecular evidence proved most efficient for distinguishing nemertean species when crypticism existed. In recent years, DNA-based approaches have been successfully used to delimit species and discover cryptic species in different nemertean groups (e.g., Strand and Sundberg, 2005;Sundberg et al, 2009a;Sundberg et al, 2009b;Chen et al, 2010;Fernańdez-A ́lvarez and Machordom, 2013;Leasi and Norenburg, 2014;Kang et al, 2015;Sundberg et al, 2016b;Krämer et al, 2017;Chernyshev et al, 2018;Sagorny et al, 2019). The approach combining molecular and morphological information has been becoming a standard method for describing new species of nemerteans (Strand and Sundberg, 2011;Strand et al, 2014;Hiebert and Maslakova, 2015;Kajihara et al, 2018a).…”

Genome Size Dynamics in Marine Ribbon Worms (Nemertea, Spiralia)

“…By adding new data, covering morphologically divergent lineages, such as Cephalotrichidae as well as known ecological and developmental variation of the phylum [14,[37][38][39][40][41][42][43][44], we aimed to (1) analyze the distribution and potential evolutionary consequences of genome size variation in the phylum Nemertea. More specifically, within a novel phylogenetic framework, we aimed to (2) test the correlation of body length and genome size as well as (3) relate genome size to habitat and several functional and developmental traits.…”