Shedding light on a species complex within the genus Goniodoridella Pruvot-Fol, 1933 (Nudibranchia: Goniodorididae), with the description of three new species

Goniodoridella Pruvot-Fol, 1933 is a genus of small nudibranchs found in the Indo-Pacific Ocean. Currently, the genus includes only two described species, the widely distributed type species Goniodoridella savignyi Pruvot-Fol, 1933 and G. borealis Martynov, Sanamyan & Korshunova, 2015, which is found in the northern Sea of Japan. However, because of the presence of a group of cryptic species, the known geographic range of G. savignyi may have been overestimated, while the species richness of the genus may be underestimated. In the current study, we examined specimens from Australia, the Philippines and Russia that were identified as G. savignyi, G. borealis and an undescribed species. Detailed analyses of the external morphology and internal anatomy of the specimens were carried out, as well as scanning electron micrography of the radula and the labial cuticle. Photographs of the penial spines were taken under a light microscope. DNA sequence data for selected mitochondrial and nuclear markers were obtained, allowing the inclusion of the genus Goniodoridella in molecular phylogenetic analyses for the first time. Our results support the monophyly of the genus Goniodoridella and confirm the existence of a species complex of which the type is G. savignyi. The new species G. geminae n. sp., G. serrata n. sp. and G. unidonta n. sp. are described.