Hiding in plain sight-Euplokamis dunlapae (Ctenophora) in Norwegian waters.

Xabier Irigoien,Sanna Majaneva,Ellie Johansen,Aino Hosia,Mari-Ann Østensen,Halldis Ringvold

doi:10.1093/plankt/fbab012

Abstract

Cydippid ctenophores of genus Euplokamis have been rarely reported from the north-east Atlantic in the scientific literature. The conspicuous lack of previous records is likely attributable to methodological constraints detrimental to sampling ctenophores, including the use of plankton nets and preservation of samples as well as poor identification literature and a lack of taxonomic expertise on gelatinous zooplankton. Here, we have compiled published and novel records as well as documented diver observations, of Euplokamis spp. in Norwegian waters. Despite scant earlier reports, our data suggest that the genus Euplokamis is widely distributed and relatively common along the entire Norwegian coast, including Svalbard. Euplokamis was recorded from samples taken from several hundred meters depth to surface, from fjords as well as offshore. Most of the observations reported in this study are from the period between April and July, whereas specimens have been found nearly throughout the year. Specimens from Norwegian waters were morphologically most similar to Euplokamis dunlapae, and conservative 18S rDNA sequences of some specimens had a 100% match with an E. dunlapae specimen from Friday Harbor, USA, the type locality for the species. However, the morphological and molecular variation of Euplokamis demonstrates the need for systematic global sampling of multiple individuals of many ctenophore species.

Highlights

The monotypic ctenophore family Euplokamididae Mills, 1987 is characterized by tentacle side branches containing striated muscle, a unique feature within the phylum Ctenophora (Mills, 1987; Mackie et al, 1988)
Mills suspects that E. octoptera may be a synonym for Mertensia ovum (Fabricius, 1780) and comments that the tentacles of E. evansae do not seem to justify its inclusion in the genus Euplokamis (Mills, 1998-present), where it was provisionally placed by Gershwin et al (2010)
The data combined for this study show that ctenophores of the genus Euplokamis have been observed along large parts of the Norwegian coast, from southern Norway to Bodø and around the Svalbard archipelago, including north of Svalbard, to almost to 82◦N (Fig. 2, Table I)

Summary

Introduction

The monotypic ctenophore family Euplokamididae Mills, 1987 (previously Euplokamidae) is characterized by tentacle side branches containing striated muscle, a unique feature within the phylum Ctenophora (Mills, 1987; Mackie et al, 1988). The genus is poorly represented in modern identification literature: The only existing key to species (excluding E. evansae) is by Mills (1987), while Gershwin et al (2010) present a table comparing diagnostic characters. Mills (https://faculty.washington.edu/ce mills/ActaErrata.html, accessed 13 February 2020) suspects that E. octoptera may be a synonym for Mertensia ovum (Fabricius, 1780) and comments that the tentacles of E. evansae do not seem to justify its inclusion in the genus Euplokamis (Mills, 1998-present), where it was provisionally placed by Gershwin et al (2010)

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Discussion

Conclusion