Pseudoilbia avellana (Schmekel & Cappellato, 2001)

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 : 782-783

Pseudoilbia avellana or Runcina avellana ?

The species Runcina avellana was originally described by Schmekel & Cappellato (2001) from Banyuls-sur- Mer, French Mediterranean. These authors found an unusual radula (3 × 1.0.1) and no gizzard plates in the single specimen examined, which they pointed out could be a juvenile. Ortea (2013), because of the absence of raquidian teeth and gizzard plates assigned the species to the genus Pseudoilbia, proposing the new combination name Pseudoilbia avellana .

Our specimens characterized by features consistent with the original description of R. avellana (sensu Schmekel & Cappellato, 2001; Fig. 9 ), like the shape of the body, presence of a round brownish mark on the centre of tail, general colour pattern, absence of gizzard plates and presence of gills, collected at Roses, Spain about 45 km from the type locality, clustered in the phylogenetic analyses among species of the genus Runcina (Clade F; Fig. 1 ), questioning the assignment by Ortea (2013) of this species to the genus Pseudoilbia. The latter genus is characterized by animals lacking gills, gizzard plates, shell and with radular formula 2.0.2 ( Miller & Rudman, 1968). Runcina avellana shares some of these features, but not all, and our phylogenetic results support its inclusion in Runcina . Moreover, the lack of rachidian teeth in R. avellana , reported by Schmekel & Cappellato (2001), might be an artefact since only one apparently juvenile specimen was studied by these authors. Unfortunately, our effort in preparing the radula of this species was not successful and, thus, we could not study this structure. Additional specimens of R. avellana are necessary to permit a detailed study of its anatomy and comparison with other species of Runcina and Pseudoilbia.

Runcina

The genus Runcina has been traditionally defined by the presence of up to four separated gills on the right side of the anus and a triseriate (1.1.1) radula with bilobed rachidian teeth and smooth or denticulated lateral teeth ( Burn, 1963; Gosliner, 1991; Schmekel & Cappellato, 2001). Our analysis supports the monophyly of the genus Runcina (PP = 1; BS = 99) but with R. avellana , which lacks rachidian tooth and, in addition, specimens resembling R. ferruginea from the Mediterranean coasts of Spain and France, and from Croatia clustered elsewhere in the tree together with other runcinids from Bermuda, Hawaii, Brazil, Japan, Russia and also from the Atlantic coast of France (PP = 1; BS = 78).

We have included in our phylogenetic analysis about 39% of the nominal species of European Runcina (MolluscaBase, 2021) and, in addition, several unidentified specimens from Spain, Italy and Croatia ( Fig. 1 ). Within Runcina , we retrieved a clade (PP = 1; BS = 100) containing one specimen that we provisionally have identified as R. cf. bahiensis , one specimen provisionally identified as R. hornae and several unidentified specimens. Most specimens in this clade were collected in Catalonia (northeastern Mediterranean Spanish coast) and, despite the remarkable variation in colour pattern ( Fig. 10 ), species delimitation analyses suggest they all belong to the same species (COI uncorrected p -distances varied between 0.0–2.0%).

The species R. bahiensis was originally described from the Bay of Algeciras (Strait of Gibraltar, Spain) ( Cervera et al., 1991) and R. hornae from Banyulssur-Mer (Mediterranean coast of France) ( Schmekel & Cappellato, 2002). Both species have been reported in several localities in Catalonia ( Sánchez-Moyano et al., 2000; Ballesteros et al., 2016), and are regarded as differing in colour pattern, number of rows of radular teeth, shape of body and presence of small protuberances ( Cervera et al., 1991; Schmekel & Cappellato, 2002). Several of our specimens ( Fig. 10B– D ) bear a colour pattern and body shape consistent with R. bahiensis , but none of them have the small protuberances characteristic of this species. The study of a radula of one specimen from Catalonia ( Runcina sp. 3 ) matched the original description of the radula of R. hornae ( Schmekel & Cappellato, 2002; Fig. 11 ). Unfortunately, specimens of R. bahiensis from the type locality or nearby were not available for this study, but considering the radular similarities and the proximity to the type locality of R. hornae (c. 25.5 km), we identify specimens is this clade as R. hornae , which is here demonstrated to be a species with remarkable colour variability ( Fig. 10 ).

Figures

Figure 1. Phylogenetic hypothesis of the order Runcinida based on the combined genes H3, COI, and 16S inferred by Bayesian analysis. Numbers on the left of the slash are posterior probabilities and on the right bootstrap values derived from maximum likelihood analysis. A, ABGD results based on the COI dataset. B, bPTP results based on the COI dataset. Rectangles in Ilbia ilbi are missing since there is no COI sequence available. Abbreviations: ATL, Atlantic Ocean; MED, Mediterranean Sea. *, branches with maximum support. 1, refers to sequences from Genbank.

Figure 9. Runcina avellana. A, schematic illustration taken from Schmekel & Cappellato, 2001 (original description). B, living animal from Catalonia, north-eastern Spain (Mediterranean Sea) (MNCN 15.05/88108, 1,5 mm in length). Image B by Ana Karla Araujo.

Figure 10. Living animals of Runcina hornae. Specimens from Catalonia, north-eastern Spain (Mediterranean Sea). A, MNCN 15.05/88104, 1 mm in length. B, MNCN 15.05/90661, 1 mm in length. C, MNCN/AND 118954, 2 mm in length. D, MNCN 15.05/90656, 1.5 mm in length. E, MNCN 15.05/90660, 3 mm in length. F, MNCN 15.05/90655, 3 mm in length. G, MNCN 15.05/90659, 2.5 mm in length. H, MNCN 15.05/90665, 1.5 mm in length. I, MNCN 15.05/90658, 1.5 mm in length. J, MNCN 15.05/90654, 2 mm in length. L, MNCN 15.05/90657, 1 mm in length. M, MNCN 15.05/90662, 2 mm in length. N, MNCN 15.05/90664, 3 mm in length. O, MNCN 15.05/90663, 1 mm in length. P, MNCN 15.05/88110, 2 mm in length. Images A, E, G, H courtesy of Carlés Galià; images B, F, M, N, O courtesy of Marina Poddubetskaia; images C, D, I, J, L, P by Ana Karla Araujo.

Figure 11. Scanning electron micrographs of radula of Runcina hornae (MNCN 15.05/90654, 1 mm in length, Mataro, Spain). A, rachidian teeth. B, lateral teeth. Scale bars: A = 5 μm; B = 10 μm.