Deviant unicorns: monocerate and dicerate versions of Carlotta Roewer, 1943 (Opiliones: Gonyleptidae), with description of four new species from Eastern Brazil

In this study, the understanding of the harvestman genus Carlotta Roewer, 1943, is expanded. Carlotta currently comprises two species found in central Espírito Santo state. The descriptions of the existing Carlotta species have been supplemented, including genital morphology. Four new species are herein described—Carlotta beckeri sp. nov., Carlotta bicornis sp. nov., Carlotta iohannis sp. nov. and Carlotta obtortrix sp. nov.—extending the range of the genus both southwards and northwards from southern Espírito Santo to southern Bahia. Among the new findings, a unique trait is exhibited by two species: a pair of spines on the ocularium (dicerate), in contrast to a single spine (monocerate). This variation is significant, as the number of spines on the ocularium plays a crucial role in the Roewerian diagnosis for the genus. The characterisation of the genital morphology of Carlotta species is refined, with the identification and naming of two distinctive structures: the dilophium—two parallel lamellate ridges along the disto-ventral surface of the stylus, terminating in a broader loop—and the skeletal flabellum—a framework of arched cylindrical tapering branches with multiple ramifications. By shedding light on these newly identified structures, a more comprehensive understanding of the diversity and evolutionary traits within the Gonyleptidae is contributed through this study.