Resolving the taxonomic identities and genetic structure of two cryptic Platynereis Kinberg species from South Africa

Abstract

The perceived cosmopolitanism of polychaete worms could be an artefact of historical factors such as poor original species descriptions, lack of type material and the European taxonomic bias, to name a few. Thus, it is possible that several cosmopolitan species hide complexes of cryptic and pseudocryptic species. Two putative cosmopolitan species, Platynereis dumerilii and Platynereis australis, collected in South Africa were investigated here (1) to determine whether the South African taxa are conspecific with the morphologically identical taxa from France and New Zealand (the respective type localities of P. dumerilii and P. australis), (2) to compare the South African species morphometrically to determine whether their morphological characters are reliable enough to separate them, and (3) to investigate whether these species have geographically structured populations along the coast of South Africa. Molecular data (COI and ITS1) confirm that P. dumerilii and P. australis do not occur in South Africa. Instead, the South African taxon formerly thought to be Platynereis dumerilii is new and is described here as Platynereis entshonae, sp. nov.; the identity of the other South African species is currently unresolved and is treated here as Platynereis sp. Surprisingly, Platynereis massiliensis (type locality: Marseilles) nested within the South African Platynereissp. clade but, since it is part of a cryptic species complex in the Mediterranean, the name is considered doubtful. Morphological characters traditionally used to define these South African Platynereis species are not reliable as predefined morphological groupings do not match phylogenetic clades and principal component scores revealed no separation in morphological characters that could distinguish between them. Haplotype networks and phylogenetic trees revealed that P. entshonae, sp. nov. and Platynereis sp. have geographically structured populations along the South African coast. http://zoobank.org/urn:lsid:zoobank.org:pub:6E36A210-9E48-430F-8A93-EDC27F0C5631

Character investigation and homology, with a brief discussion on the phylogenetic relationships of Annelida and Polychaeta within Metazoa

“…We conclude that genetic data are very important for the recognition of distinct populations, being a useful tool for the recognition of species, as performed in several molecular studies. In particular, we illuminate the case of species-complexes, where morphology is unable to distinguish valid subgroups (Wheeler, 2005;Álvarez-Campos et al, 2016;Budaeva et al, 2016;Saglam et al, 2016;Kara et al, 2020). For the hypotheses of phylogenetic relationships among larger groups, such as phyla, classes and orders, molecular data should however be avoided, even in the case of multiple genes.…”

The Nereid on the rise: Platynereis as a model system

“…The mitochondrial genome of P. dumerilii has been sequenced [ 159 ]. Mitochondrial genome data is also available for other Platynereis species, as a basis for Platynereis species trees [ 159 , 160 ]. Studies are also underway for sequencing genomes of sister Platynereis species such as P. massiliensis and P. megalops .…”

Taxonomic status and phylogeographical structure in Pseudonereis sp. East Asia in the East China Sea off the Coast of Zhejiang, China

“…Noticeable variations in morphology and genetics raised the question whether individuals from distinct ocean basins belong to the same species ( Kara et al 2020). So far, there is compelling evidence for the occurrence of cryptic species in P. variegata, e.g.…”