The identity of juvenile Polynoidae (Annelida) in the Southern Ocean revealed by DNA taxonomy, with notes on the status of Herdmanella gracilis Ehlers sensu Augener

Abstract

Using molecular data (CO1, 16S and H3 genes), we provide evidence for a long-held view that Southern Ocean scaleworms (Polynoidae) morphologically agreeing with Herdmanella gracilis sensu Augener, 1929 Ehlers sensu Augener are in fact juveniles of another species. The problematic genus Herdmanella is declared a nomen dubium. Importantly, at least two species were identified; one adult counterpart is a common circumpolar species, Austrolaenilla antarctica Bergström, 1916, and the other is of an as yet unknown identity. More adult counterparts are likely to be discovered with greater sequencing effort and larger taxon coverage. We have discovered a great genetic diversity within the A. antarctica clade in the CO1 gene, and future studies may elucidate if this represents a cryptic species. Currently, we adopt a conservative approach and suggest that given low diversity in mt16S and complete identity in H3 genes, this clade represents a single species, with only the specimen from South Georgia likely deserving the status of a cryptic species, as shown by haplotype network analysis. High mtDNA diversity in populations of Antarctic scaleworms may be linked to habitat fragmentation during recent glacial periods. Our study also highlights the importance of identifying juvenile specimens correctly in order to understand ecological processes such as the apparent high productivity in the Amundsen Sea region.

Comparative marine biodiversity and depth zonation in the Southern Ocean: evidence from a new large polychaete dataset from Scotia and Amundsen seas

“…For consistency, a large number (∼2500) of polynoid juveniles (see Neal et al 2014 for details) and undeterminable specimens were removed from the analyses, resulting in the final dataset of 16,991 specimens.…”

“…The use of DNA techniques for taxonomic purposes has revealed the existence of cryptic species in Southern Ocean fauna (e.g. Barnes et al 2011), including polychaetes (Schüller 2010;Neal et al 2014;Brasier et al 2016). Some eurybathic species may in fact be species complexes, with restricted depth ranges, contradicting the extended eurybathy hypothesis, as already demonstrated for Glycera kerguelenis McIntosh, 1885 (see Schüller 2010).…”

“…This finding is relevant to data presented here as Glycera kerguelensis (as established by morphological examination) was abundant at all depth horizons in the Amundsen Sea. Neal et al (2014) suggested that a haplotype of Austrolaenilla antarctica from South Georgia may represent a different species to those from the Amundsen and Weddell Seas, while a wide geographic range of Austrolaenilla pelagica between the Amundsen and Ross Seas has been shown. The biogeographic and bathymetric patterns in polychaete morphospecies targeted by Brasier et al (2016) are currently being investigated further (Brasier, personal communication).…”

“…However, it is important to stress that much of the contribution to this species richness, (particularly in the Amundsen Sea) comes from new, undescribed species. Throughout the identification process, there was a concern that some species that key out to taxa considered cosmopolitan or circumpolar may be Bcryptic^species as already discussed (Neal et al 2014;Brasier et al 2016). Therefore, the 307 species reported here must be an under-representation of the total polychaete species diversity.…”

“…Polychaetes are prone to fragmentation and most worms were posteriorly incomplete, many polynoidae were missing their scales and it was not practical to dissect jaws and proboscis in many, particularly small specimens. A large number of specimens were also revealed to be juveniles, which can show very different morphology from their adult counterparts (Neal et al 2014), but knowledge of such developmental stages of Southern Ocean polychaetes is very rare. Recently Brasier et al (2016) published molecular results on subset of 16 morphospecies from this study, leading to the addition of extremely valuable and rare molecular data for Southern Ocean polychaetes.…”