Revealing morphological characteristics of Goniodorididae genera (Mollusca: Nudibranchia)

Detailed knowledge of the anatomy of the species is an essential element in taxonomic studies, since it allows the comparison and differentiation of separate groups of taxa. It becomes especially important when considering type species, as the subsequent identification of the species that compose the taxa is based on its characteristics, considered common in the group. However, despite its relevance, there are still numerous species without detailed descriptions, being especially significant among invertebrates. The family Goniodorididae is a little-known group of nudibranchs that includes eight recognized genera: Okenia, Goniodoris, Ancula, Lophodoris, Spahria, Trapania, Goniodoridella and Murphydoris. Several of their species are not completely described, including type species, and the systematics of the family is still unclear. Here we study in detail the external morphology and internal anatomy of the type species of five of the eight Goniodorididae genera using microcomputed tomography and scanning electron microscopy. We include the species Okenia elegans, Goniodoris nodosa, Ancula gibbosa, Goniodoridella savignyi and Murphydoris singaporensis as well as one species of Trapania, T. graeffei. We describe for the first time the detailed internal anatomy of the type species Goniodoridella savignyi. The diagnostic features of each genus are compared, and a preliminary framework is shown to clarify their systematics and identifications.