A species complex within the red-reticulate Goniobranchus Pease, 1866 (Nudibranchia: Doridina: Chromodorididae)

The taxonomy and diversity of chromodorid nudibranchs (Mollusca: Gastropoda: Nudibranchia) are relatively well-studied, although molecular analyses have only been applied to test few species-level groups. Within Chomodorididae, the genus Goniobranchus Pease, 1866 contains many different groups based on external colouration, including the red-reticulate group. Previously, most of the red-reticulate group has been considered as either a single variable species, identified as either Goniobranchus reticulatus Pease, 1866 or Goniobranchus tinctorius (Ruppell & Leuckart, 1828), or as a species complex. In this study, red-reticulate nudibranchs were collected from different locations spanning the Indo-Pacific. From these specimens, DNA data were derived, consisting of mitochondrial cytochrome c oxidase subunit I (COI) and 16S ribosomal DNA (16S rDNA) sequences. COI data were analysed using a distance-based species delimitation approach (ABGD), and the combined dataset (COI+16S rDNA) was analysed using maximum likelihood (ML) and Bayesian inference (BI) methods. The analyses identified five species-level clades, but none of the clades’ morphotypes matched exactly with the original descriptions of G. tinctorius or G. reticulatus. The non-reticulate, spotted species Goniobranchus splendidus (Angas, 1864) falls inside this complex. The existence of multiple species-level clades in the Goniobranchus red-reticulate group suggests this is a group of closely related species, comprising at least five undescribed taxa.