Range extension for the region of sympatry between the nudibranchsHermissenda opalescensandHermissenda crassicornisin the northeastern Pacific

Emily M Merlo,Kathryn A Milligan,Dirk Steinke,Nola B Sheets,Paul D.N Hebert,Tao M Eastham,Russell C Wyeth,Ángel Valdés,A.L Ka’Ala Estores-Pacheco,Christopher J Neufeld,Jeremy Kerr

doi:10.1139/facets-2017-0060

Abstract

The mollusc nudibranch genus Hermissenda Bergh, 1879 was recently discovered to include three pseudocryptic species, dividing a single species H. crassicornis (sensu lato) into H. crassicornis Escholtz, 1831, H. opalescens J.G. Cooper, 1863, and H. emurai Baba, 1937. The species were distinguished by both genetic and morphological evidence, and the distribution of sampled animals suggested the three species had mostly distinct geographical ranges. Here, we report the presence of both H. crassicornis and H. opalescens in Barkley and Clayoquot Sounds, British Columbia, Canada, based on diagnostic characters and molecular data congruent with the differences described for these two species. This result extends the region of sympatry for the two species from northern California, USA, to, at least, Vancouver Island, British Columbia in 2016. Depending on how long this overlap has occurred, the possible northward expansion of H. opalescens would have implications for understanding the effects of short- or long-term environmental changes in ocean temperatures as well as complicating the interpretation of past neurobiological studies of H. crassicornis (sensu lato).

Highlights

The heterobranch sea slug genus Hermissenda Bergh, 1879 was recently determined to include three pseudocryptic species: H. crassicornis Escholtz, 1831; H. opalescens J.G
The characteristics for each were consistent with those described for H. crassicornis and H. opalescens (Lindsay and Valdés 2016) and field identification was confirmed with molecular data from five individuals belonging to the two species
H. opalescens had no white stripes on their cerata, the distal sections of the cerata were white, and the animals were consistently larger with proportionately wider feet

Summary

Introduction

The heterobranch sea slug genus Hermissenda Bergh, 1879 was recently determined to include three pseudocryptic species: H. crassicornis Escholtz, 1831; H. opalescens J.G. Cooper, 1863; and H. emurai Baba, 1937 (Lindsay and Valdés 2016). The three species were distinguished by genetic analyses, morphological characters, and geographic ranges in the North Pacific (Table 1). This division has resurrected the three species names originally described in the genus that had previously been unified into a single trans-Pacific species, H. crassicornis (sensu lato) (O’Donoghue 1922). Short Translucent to white Orange (light to bright in hue). Range from light to dark brown; may be bright orange. May or may not contain reddish to brown tipping Absent Small

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Conclusion