Assessment of the status and distribution of the poorly known nudibranch Madrella aurantiaca (Gastropoda, Nudibranchia, Madrellidae)

Among the limited number of species currently included in the nudibranch genus Madrella Alder & Hancock, 1864, only one has been documented from European waters. Nevertheless, our knowledge of the distribution and biology of this species remains limited, largely due to the paucity of observations, which are confined to a small number of records from the Mediterranean and the north-east Atlantic. During a series of sampling dives conducted in Galicia to catalogue benthic fauna, a single specimen of Madrella aurantiaca Vayssière, 1902 was discovered. Given the scarcity of records for this species, the specimen was photographed and collected for further study. Additional specimens captured in the Balearic Islands (western Mediterranean) during the FAUNA III oceanographic campaign were also examined in order to compare and update the available information on the species. As a result, new data on morphology and biology are presented, including a description of the egg masses. Historical records of the species are also reviewed, providing an overview of its current status and an updated distribution. The addition of new records for such a rarely reported species is of considerable value for improving our understanding of its distribution and biology, and ultimately for refining our knowledge of global diversity.