For my second entry in our advent calendar, I will again present a taxonomic paper. This time it is surprisingly not about worms, but about a rather intriguing group of crustaceans, Facetotecta (Figure 1). It is a small group of about 14 species, all in the genus Hansenocaris. What is so fascinating about these animals is that only larval stages are known. Adults have never been observed and remain unknown.
In their paper, Ølesen et al. developed an integrative approach combining laboratory rearing, DNA sequencing and morphological studies. Using these methods the authors study several species and describe a new one. I find the use of laboratory rearing and the inclusion of several life stages in the description particularly interesting as it is very rarely done. To keep specimens in the laboratory can often be complicated but it is something I would very much like to try to complete species descriptions. Finally, I really enjoyed the beautiful and detailed plates included in this paper.
Reference: Ølesen J., Dreyer N., Palero F., Eibye-Jacobsen D., Fujita Y., Chan B.K.K., Grygier M.J. 2022. Integrative taxonomy of crustacean y-larvae (Thecostraca: Facetotecta) using laboratory-rearing and molecular analyses of single specimens, with the description of a new vermiform species. Zoological Journal of the Linnean Society 196 (1): 549–592.