The red crab Ucides occidentalis (locally called "guariche") is widely distributed along Ecuador's coastline and is the most important crustacean fishery exploited by local coastal communities. However, a lack of information on the species' reproductive cycle has hindered conservation and sustainable management initiatives. Here we documented for the first time the complete embryonic development of U. occidentalis, based on its morphological traits. Thirteen ovigerous females were collected in the field, maintained in captivity, and fed with leaves and tender mangrove propagules. Egg samples were taken every 12 h and analyzed under the microscope to evaluate embryonic development. U. occidentalis eggs had eight different embryonic stages, which maintained their spherical shape during the entire developmental. The eggs were relatively small and uniform in size. The tenuous heart beating of the precursor coincided with the formation of chromatophores in stage V and became more frequent at stage VIII, just before hatching. The incubation period lasted 15 days. Despite the rapid development, the increase in egg size and volume was not uniform during sequential stages.In Ecuador, Ucides occidentalis is distributed along the entire continental coastline and is known as "red crab" or "guariche". The species is also the most economically important crustacean exploited by Ecuadorian coastal communities. The present study makes the first documented description of the complete embryonic development of the red mangrove crab U. occidentalis, based on its morphological characteristics. Thirteen ovulated females were obtained from the natural environment, which were stored in previously conditioned containers, where they were fed with leaves and tender mangrove propagules. The spawn was collected and taken to the microscope for illustration and description of development every twelve hours. U. occidentalis eggs had 8 different embryonic stages, maintaining their spherical shape during the entire development. The eggs are relatively small and uniform in size, the tenuous beating of the heart precursor coincides with the appearance of chromatophores in stage V and becomes more frequent up to stage VIII before hatching. The incubation period was fifteen days before hatching and despite the development, the growth in egg volume is not significant.