The aim of this Ph.D. dissertation is to increase the knowledge about cosmopolitan and parthenogenetic earthworms. For this purpose, the earthworm Eiseniella tetraedra (Savigny, 1826) was chosen as a model. Although there have been studies on other earthworm species with the same characteristics, no work has ever been done that includes so many individuals and populations. On the other hand, its relationship with other species of the same genus has been studied using molecular markers and traditional techniques such as the study of its morphology. Finally, new generation sequencing techniques were used to determine changes in the gene expression profile of E. tetraedra under different abiotic stressors…