Moina eugeniae is the most abundant species in the southwest lagoons of Buenos Aires province. The aim of this work is to study the histology of this cladoceran by light microscopy so as to expand the knowledge of this species. The parthenogenetic females were fixed in formaldehyde 4%. Sections were cut 3 µm thick and stained with Hematoxylin and Eosin. The intestine has simple cuboidal epithelium with apical projections and the cells have 1 or 2 nucleoli in their nuclei. Two compound eyes were found and no naupliar ocelum. The ovary is saccular and it is presented in a pair at both sides of the intestine with follicles in different states of development. The striated muscle with notorious microfibrills is recognized in antennas, antennules and trunk appendices. This article may represent the first detailed description of the histology of this species.Fil: Elias, Fernanda Gabriela. Universidad Nacional del Sur; ArgentinaFil: Cervellini, Patricia Marta. Universidad Nacional del Sur; ArgentinaFil: Garibotti, Emilio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin
