Runcina coronata (Quatrefages, 1844)

Araujo, Ana Karla, Pola, Marta, Malaquias, Manuel Antonio E, Ballesteros, Manuel, Vitale, Fabio & Cervera, Juan Lucas, 2022, Molecular phylogeny of European Runcinida (Gastropoda, Heterobranchia): the discover of an unexpected pool of complex species, with special reference to the case of Runcina coronata, Zoological Journal of the Linnean Society 194 (3), pp. 761-788 : 783

Runcina coronata species complex

In the last few years, several complexes of species have been detected among heterobranch sea slugs (see, among others: Jörger & Schrödl, 2013; Padula et al., 2014; Carmona et al., 2015; Krug et al., 2016; Korshunova et al., 2017; Austin et al., 2018). In Runcinida , the first complex of species was unravelled by Araujo et al. (2019) for the species Runcina brenkoae with the description of two new species, namely R. marcosi and R. lusitanica .

In the current study, molecular and morphological data have showed that R. coronata hides a complex of at least four species, including two new to science and the previously described species R. aurata . Due to similarities with the original description by Quatrefages (1844), and the descriptions provided by Forbes (1851) and Schmekel & Cappellato (2002), we regard our specimens from Swanage ( England) conspecific with R. coronata .

The geographical distribution of R. coronata has been reported to extend from England to the French Mediterranean coast ( Vayssière, 1883; Cervera et al., 2004). However, our results questioned the presence of R. coronata in the Iberian Peninsula, where most likely the records to this species belong to R. aurata (see in Results, ‘Remarks’ section of R. aurata ). The morphological differences between specimens identified as R. coronata in the Mediterranean Sea and those from England and the Atlantic coast of France suggest, as previously stressed by Burn (1963), that animals studied by Vayssière (1883) from the Mediterranean are a distinct species and also that R. calaritana ( Colosi, 1915) could be a valid name.

Therefore, we here restrict the distribution of R. coronata to southern England and the Atlantic coast of France, a limited geographical span supported by the direct development of the species ( Schmekel & Cappellato, 2001). The species R. aurata and R. caletensis , despite subtle differences, are externally difficult to distinguish and coexist in the same geographical area (Cádiz, south of Spain), whereas the species R. tingensis is so far only known from the north-western coast of Morocco.

This work has revealed several additional putative cases of hidden diversity among runcinids in Europe (e. g. R. adriatica and R. ferruginea ), and our detailed study of the R. coronata species-complex has made it possible to redefine the type species of the genus, to clarify the taxonomic status of R. aurata and to describe two new species to science. In addition, we have provided the first modern approach to understanding relationships in the order Runcinida and a provisional framework to discuss the familial and generic classification of the group.