The study of all levels of biodiversity is crucial to understand the evolutionary, biogeographical and phylogeographical patterns of species. The basal level of biodiversity is the genetic diversity, and a population genetics approach allows the quantification of that diversity and the description of its distribution. In most Squamates (a group of reptiles showing scales) remains unknown how much genetic diversity exists and how is it scattered in the geographical range of the populations. This is evident in Amphisbaena caeca, a soil-dwelling squamate endemic to Puerto Rico. Due to its limited mobility in the soil, each population of A. caeca could have unique and distinctive traits, resulting in cryptic diversity (i.e. biological species not easily identifiable by morphology). This proposal aims to (1) quantify the intra-population and inter-population genetic variation of A. caeca; (2) estimate its population structure degree; and (3) measure the morphological variation in the species. We will estimate the nucleotide and haploytpe diversity of each population. The population structure degree will be measured by the Nst estimator and by calculating the migration rates between populations. A hierarchical AMOVA (Analysis of Molecular Variance) will help to understand how the genetic diversity is organized in the geographical range. We will estimate the effective size of each population to know how many individuals are contributing to the genetic diversity. With all this information, we expect to significantly contribute to the taxonomy of this group by describing subspecies or species previously not identified in classic morphological studies. We will define Evolutionary Significant Units (ESUs) that will contain populations with conservation priorities due to their uniqueness and distinctiveness. Finally, this project also pursues to inform Puerto Rican people about this group of animals, especially in rural and suburban areas. In those areas, the lack of knowledge about this animal lead people to confuse them with other soil fauna (e.g. earthworms). Moreover, accidental or intentional deaths by people are common in these animals, even when they constitute a key element in the alimentary chains of the soil and we do not know anything about their conservation status.