Ovarian Follicular Typology in Coypu ( <scp> <i>Myocastor coypus bonariensis</i> </scp> )

The coypu (Myocastor coypus bonariensis) is a semi-aquatic hystricomorph rodent native to South America, widely distributed across wetlands from southern Brazil to Tierra del Fuego. The general features of the ovary of the coypu older than 6 months are similar to those described for other hystricomorphs. The objective of this research was to expand the qualitative and quantitative characterization of the follicular typology of coypu at sexual maturity. We worked with 36 ovaries from females in different stages of the oestrous cycle. The follicles were analysed based on qualitative and quantitative characteristics, such as their size (mean follicular diameter and number of granulosa cells), size of each oocyte and its nucleus, presence of zona pellucida, antrum, and theca. Six follicular types were established, subdivided into 12 subtypes. Establishing this follicular typology in a South American species advances comparative studies. Additionally, it enables a deeper analysis of follicular development across different species.