Phestilla Bergh, 1874

Wang, Adam, Conti-Jerpe, Inga Elizabeth, Richards, John Lawrence & Baker, David Michael, 2020, Phestilla subodiosus sp. nov. (Nudibranchia, Trinchesiidae), a corallivorous pest species in the aquarium trade, ZooKeys 909, pp. 1-24 : 1

Genus Phestilla Bergh, 1874

Diagnosis.

"Physical form quite depressed. An edge anterior to the head, wing-like, attached to [...]; oral tentacles short, rhinophores simple. Cerata arranged on singular slanting rows, lacking cnidosacs. [...] Masticatory edge contains mandibles behind teeth (round, with irregular serration). Radula uniserial." - Bergh, 1874: 1, partially translated.

Included species.

Phestilla chaetopterana (Ekimova, Deart & Schepetov, 2017), comb. nov., Phestilla lugubris (Bergh, 1870), Phestilla melanobrachia (Bergh, 1874), Phestilla minor (Rudman, 1981), Phestilla panamica (Rudman, 1982), Phestilla poritophages (Rudman, 1979), Phestilla subodiosus sp. nov.

Remarks.

Historically, Phestilla was placed in the family Tergipedidae . This family contained a large "unnecessary and unnatural" number of genera ( Rudman 1979: 344). Phylogenetic analysis revealed that this grouping was polyphyletic and a "radical solution" ( Cella et al. 2016: title) was proposed: several families were combined into the family Fionidae , and several genera, including Phestilla , into the genus Tenellia ( Cella et al. 2016). However, a study into the ontogeny of these groups elucidated that Cella et al.'s (2016) taxonomic decisions were underrepresenting the molecular, ecological, morphological, and ontogenetic diversity of the clades; thus, the families and genera that were combined into Fionidae and Tenellia were reinstated ( Korshunova et al. 2017c). While there is controversy surrounding which interpretation is the taxonomic truth, we have designated Phestilla as a separate genus to Tenellia based on the arguments presented by Korshunova et al. (2017c). However, given the results of the p -distance and ABGD analysis, we follow Cella et al. (2016) and Rudman’s (1981) decisions to synonymize P. sibogae with P. lugubris .

At the same time that Korshunova et al. (2017c) published their findings, Ekimova et al. (2017) published a paper describing Tenellia chaetopterana , a species that clusters phylogenetically and morphologically with Phestilla . As both papers were released on the same date (26 September 2019), Ekimova et al. (2017) were unable to incorporate the revised designations from Korshunova et al. (2017c) into their description. However, there are considerable differences between Te. chaetopterana and the other Phestilla species. Firstly, the radular cusp and lateral denticle proportions are unique in the entire family ( Korshunova et al. 2017c), but the general pattern is similar. Secondly, the species lacks penile glands or bulbs. Thirdly each ceratal row only has a single cerata ( Ekimova et al. 2017). Finally, Te. chaetopterana would represent the first Phestilla species that does not feed on scleractinian corals ( Rudman 1979, 1981, 1982; Goodheart et al. 2017). Further research is required to determine whether Te. chaetopterana should represent a new genus or another species of Phestilla . Based on our independent phylogenetic analysis and the synapomorphies shared by Te. chaetopterana and Phestilla , we propose transferring Te. chaetopterana to the genus Phestilla as the most parsimonious solution.