Abstract: Phenotypic variation in the sea urchin Eucidaris tribuloides (Cidaroida: Cidaridae) along the Corridor of the Southwestern Gulf of Mexico. The intraspecific morphological variation can be attributed to the result of the genetic variation or the influence of environmental heterogeneity. In the latter case, the organisms are exposed to diverse environmental conditions which have an influence on their biological processes and can be seen reflected in the morphological adaptations of the species. Indeed, the Reef Corridor of the Southwest Gulf of Mexico (CASGM, in its Spanish acronym) is constituted of geographically separated reefs that are exposed to different large-scale oceanographic factors and show their own attributes with multiple environmental variables. Therefore, this can stimulate the morphological variations of the populations of the species that are distributed in this corridor. The aim of this study was to determine the morphological variation of the Aristotle’s lantern of the sea urchin Eucidaris tribuloides along the CASGM. It was analyzed the allometric relation between the height of the Aristotle’s lantern and the diameter of the test of 104 specimens, we also used a covariance analysis to detect allometric differences between group. Apart from that, the variation of the shape of a rotule and a demi-pyramide for each sea urchin were analyzed using geometric morphometry. The results of this present study showed allometric differences among the reef systems in the north, center and south of Veracruz. The shape of the rotula and demi-pyramid of sea urchins of the north zone are different from the central and south area. However, there were no differences in shape between the center and the south area. The centroid size of the rotula and demi-pyramid of the sea urchins of the north are larger than those in the center and south. These results can be explained mainly by the geographical and environmental gradients of the CASGM, in addition to the feeding habits of E. tribuloides and the availability of the food resource in the habitat where they are established. As a stimulus to the morphological variation found in this research is also considered the distance among the reef systems and the marine currents patterns.