Material associated with the roots of mangrove in the Cispatá Bay (Department of Córdoba, Colombia) was collected during surveys carried out to determine the composition and seasonal changes of the populations of decapods crustaceans in this Department between June 2005 and May 2006. At Punta Nisperal and Caño Mocho stations, several specimens of crabs belonging to the Xanthoidae superfamily with malformations were captured.Malformations included the fusion of the anterolateral teeth, malformation of the dactyl in the form of a spiral-like walking appendix, overgrowth of pleopods in females, as well as the incidence of diseases such as black spots and subsequent destruction of the chitin layer. During the first sampling (July 2005), five specimens with deformations were collected in Caño Mocho (2.4%), and 67 in Punta Nisperal (3.8%). The incidence of malformations was associated to the rainy season, during which the discharge of the Sinú River increases and with it the discharge of polluting nutrients which can induce alterations during the larval phase (teratogenicity), resulting in the malformations described. Recent studies have shown that the constant input of metals such as mercury, classified as a teratogenic agent, is most likely the cause of this problem. © 2015. Acad. Colomb. Cienc. Ex. Fis. Nat. All rights reserved.