First true brackish-water nudibranch mollusc provides new insights for phylogeny and biogeography and reveals paedomorphosis-driven evolution

Abstract

A unique example of brackish water fjord-related diversification of a new nudibranch genus and species Bohuslania matsmichaeli gen. n., sp. n. is presented. There are only few previously known brackish-water opisthobranchs and B. matsmichaeli gen. n., sp. n. is the first ever described brackish-water nudibranch with such an extremely limited known geographical range and apparently strict adherence to salinity levels lower than 20 per mille. Up to date the new taxon has been found only in a very restricted area in the Idefjord, bordering Sweden and Norway, but not in any other apparently suitable localities along the Swedish and Norwegian coasts. We also show in this study for the first time the molecular phylogenetic sister relationship between the newly discovered genus Bohuslania and the genus Cuthona. This supports the validity of the family Cuthonidae, which was re-established recently. Furthermore, it contributes to the understanding of the evolutionary patterns and classification of the whole group Nudibranchia. Molecular and morphological data indicate that brackish water speciation was triggered by paedomorphic evolution among aeolidacean nudibranchs at least two times independently. Thus, the present discovery of this new nudibranch genus contributes to several biological fields, including integration of molecular and morphological data as well as phylogenetic and biogeographical patterns.

Fine-scale species delimitation: speciation in process and periodic patterns in nudibranch diversity

“…This pattern is very similar to what we found here for two Amphorina species. In support of the model presented here, there is evidence that a brackish-water environment, and particularly the waters in the eastern Skagerrak, Kattegat, and Baltic regions, strongly facilitates the formation of new organism groups/units that can be taxonomically evaluated from genus (Korshunova et al 2018), to species (Momigliano et al 2017) or to a specific population (Berg et al 2015).…”

Multiple paedomorphic lineages of soft-substrate burrowing invertebrates: parallels in the origin of Xenocratena and Xenoturbella

“…Furthermore, the presence of a small oral veil within Aeolidacea is a strong paedomorphic feature and is so far known only within three families; two of them are almost exclusively linked with soft-bottom environments (Pseudovermidae, Embletoniidae) and the third one to brackish waters (within family Trinchesiidae, see [44,79]), also a substantial driver for the formation of strong paedomorphic organisation. Notably, facultatively burrowing species of the complex family Cumanotidae were shown in the present study as sister to the strongly paedomorphic interstitial Pseudovermidae (Figs 1 and 2) the only representative within all Aeolidacea that displays, besides oral tentacles, also a massive veil-like enlargement of the head (Fig 3).…”

“…There is evidence that brackish water environments also facilitate developmental retardations, resulting in paedomorphosis. This is particularly well exemplified by the recent discovery of a peculiar new brackish water nudibranch genus and species [44], in a Swedish fjord. Finally, the soft-bottom meiobenthic environment has been considered a strong driver of paedomorphic organisation [6,22], thus being a very reliable example of ecological criterion for paedomorphosis.…”

From Persian Gulf to Indonesia: interrelated phylogeographic distance and chemistry within the genus Peronia (Onchidiidae, Gastropoda, Mollusca)

“…This certainly also holds for members of the intertidal living Onchidiidae. The habitat shifts and changes in abiotic factors such as salinity, temperature, oxygen level, and light intensity towards higher extremes have affected the evolution and radiation of the panpulmonate molluscs 27 – 29 . Our result on the chemical composition of P. persiae from different localities in the Gulf (Lavan Island vs. Bandar Lengeh) that generally encounter higher temperature and salinity values 3 showed a similar mixture of the main chemical features in their body extracts, thus indicating no regional differences within this species.…”