A Species richness is a critical measure in biodiversity studies, providing insights into the diversity and conservation value of ecosystems. This research presents an exhaustive inventory of crustaceans and fish species from the Yucatan Peninsula's epicontinental, underground, and anchialine aquatic systems. Spanning records from 1936 to 2024, the study analyzed over 2,600 entries across 670 aquatic systems, including cenotes, flooded caves lakes, springs, and wetlands. A total of 325 species were recorded, comprising 113 fish and 212 crustacean species. The richness and endemism of these species were assessed through a completeness analysis, utilizing non-parametric models (Chao 2, Jackknife 1, Bootstrap) to estimate potential species richness. Notably, the region exhibits high endemism, especially among crustaceans, with up of 50 species and 2 endemic families unique to the Yucatan Peninsula. The study underscores the importance of the eastern YP for crustaceans and central YP for fish, highlighting areas critical for conservation. These findings emphasize the need for further exploration, as the diversity of aquatic species remains incompletely understood. This comprehensive synthesis aims to inform future conservation strategies, environmental management, and regional planning efforts, particularly highlighting the vulnerability of these unique aquatic systems to environmental degradation.