Exploring the potential of cryo-FESEM for the taxonomic study of aquatic microcrustaceans: Bathynellacea (Crustacea, Malacostraca) as an example

The taxonomic study of microcrustaceans is a time consuming and challenging endeavor, which has slowed the rate of new discoveries, and in turn knowledge on, global aquatic biodiversity. To facilitate the study of these small organisms, new applications continually need to be explored. Here, we assess the potential use of environmental scanning electron microscopy (ESEM) techniques, specifically cryo-field emission SEM (cryo-FESEM), for taxonomic descriptions of microcrustaceans. Using a species of Parabathynellidae (Crustacea, Bathynellacea) from groundwater as a case study, we found sample preparation for cryo-FESEM to be relatively rapid and minimal compared with traditional preparation methods. The high-definition images obtained using this technique complement the drawings and digital photographs obtained using light microscopy (at 1000x). Moreover, the ability to obtain higher magnification images (up to 100,000x) allowed for a detailed observation of ultrastructures, revealing the presence of previously unreported structures in the family Parabathynellidae, including small denticles on the teeth of the dentate lobe of the male thoracopod VIII. Unfortunately, cryo-FESEM samples are too fragile to recover post-imaging and therefore cannot, at present, replace current taxonomic methods that allow for the preservation of samples, specifically holotypes and type series specimens, for future study. For cases in which many specimens are available for study, cryo-FESEM serves as a good method to supplement traditional methods to provide a more detailed description and understanding of the external morphology of a species.