Nudibranchs occur in oceans worldwide, including both the tropics and Antarctica. They live from the intertidal zone to depths of well over 700 m, e.g. a new nudibranch species was discovered recently at a depth of about 2,500 m. However, the greatest diversity of nudibranchs is seen in warm, shallow reefs.
Nudibranchs are soft-bodied marine snails that actually shed their shell after their larval stage. They are noted for their often extraordinary colors and striking forms. There are more than 3 000 described species and one of the largest groups within the order is called Aeolidida. I believe this group has the status of an infraorder and contains about 560 species.
A new phylogenetic study provides new insights into the relationships of some members of the group. The researchers were able to obtain 90 species from seven families of the Aeolidida. The researchers were specifically interested in the phylogenetic relationships within one of the families, the Aeolidiidae and they used two mitochondrial and one nuclear gene (mitochondrial COI and 16S rRNA, and nuclear H3). This is always good news for us as the inclusion of COI means there are more DNA Barcodes available to the community and these specific ones come with added value as they are part of a study that looked at the systematics of this group. The authors were not only able to resolve some previously unknown relationships and classifications, they also discovered new members:
Our results also suggest the existence of four sibling-species complexes within Aeolidiidae, which may increase to a total of 115 species, including 18 undescribed species and the resurrection of six species previously in synonymy.
Given that this is just a subset of the Aeolidida I am convinced that there are a number of similar surprises waiting for the malacologists of the world.