Insights into the cyst organisation and selected morpho-physiological aspects of encystment in Thulinius ruffoi (Parachela, Isohypsibioidea: Doryphoribiidae)

Organisms actively respond to shifts in their environment, and these responses are evident even among microinvertebrates like tardigrades. Encystment, regarded as a form of diapause, exemplifies a tardigrade’s response to environmental change. Environmental cues and unidentified internal factors regulate this process in tardigrades. While it is known that some species can form cysts, our understanding of encystment in tardigrades remains limited, necessitating further research. We investigated selected morphological and physiological aspects of encystment to improve our understanding of the organisation and physiology of encysted animals. The data collected in this study were used to examine cellular organisation, overall morphology, and anatomy, including changes during cyst formation. We also explored the relationship between the body wall and somatic muscles. This paper provides a comprehensive overview of encysted animals’ organisation, focusing on the integument and somatic muscles, as well as their role in shaping morphology during cyst formation. Additionally, the changes observed in storage cells and their significance in encystment are discussed. Despite time-dependent changes in the storage cells, our data do not support claims of organ histolysis as part of the typical changes occurring during encystment in the species we analysed.