With our colleagues from Petrozavodsk and Novosibirsk we made the first phylogenetic analysis of the parasitic copepod Caligus lacustris Steenstrup et Lütken, 1861, the only freshwater species of the genus. Its phylogenetic position implies that specialization to freshwater habitats had happened once in a group of species that included the predecessors to C. centrodonti, C. curtus, C. brevipedis, and C. lacustris itself. See the paper below for the details.

Parshukov A.*, Vlasenko P.*, Simonov E.*, Ieshko E., Burdukovskaya T., Anikieva L., … Solovyev, M. 2021. Parasitic copepods Caligus lacustris (Copepoda: Caligidae) on the rainbow trout Oncorhynchus mykiss in cage aquaculture: morphology, population demography, and first insights into phylogenetic relationships. Parasitology Research, 120 (7), 2455–2467. https://doi.org/10.1007/s00436-021-07198-5
* contributed equally to this work

Fragment of the Figure 3 from the cited work