Ostracodes (Crustacea: Ostracoda) from the Bacalar hydrological system, Mexico: new species with marine and freshwater affinities

In this study, we examined ostracode biodiversity and species taxonomy, based on morphological characteristics, from the sulfate-bicarbonate rich, oligotrophic, and freshwater Bacalar hydrological system. A total of 19 species belonging to five subfamilies were identified. Here, we describe five new species: Cypris nicte Macario-González & Cohuo sp. nov., Pseudocandona tzabek Macario-González & Cohuo sp. nov., Thalassocypria zazilha Macario-González & Cohuo sp. nov., Dolerocypria maanik Macario-González & Cohuo sp. nov., and Cyprideis ichkabal Macario-González & Cohuo sp. nov. These species are clearly distinguished from their congeners by valve outline, overall shape, or appendages morphology, particularly the male sexual appendages. Thalassocypria Hartmann, 1957, Dolerocypria Tressler, 1937, Perissocythere Stephenson, 1938, and Cyprideis Jones, 1857 are distributed worldwide only in estuarine, anchialine, and marine environments. However, their continued presence in the Bacalar system at sporadically sampling for a decade suggests that the species have successfully colonized, naturalized to freshwater, and becoming established residents, likely supported by the carbonate-related high conductivity waters. We discuss the hypothetical mechanisms underlying their inland colonization and highlight the relevance of Bacalar system as a potential ecological niche supporting their freshwater establishment and distribution.