Serracutisoma gnaspinii sp. nov. is described from the coastal Ombrophylous Dense Atlantic Rain Forest of Paraná and São Paulo states. It differs from other Serracutisoma by having a retrolateral row of spines on femur IV, a rounded white-mark on the carapace and a low dorsal apophysis on trochanter IV. It is likely the sister-species of S. proximum, and with it and other five species forms the S. proximum group, herein formally proposed. Given that the biologic, phylogenetic and biogeographic aspects of Serracutisoma have been studied, the implications of the discovery of a new species are discussed, for instance the evolution of male fight, aggregation and maternal care, traits that are shared with other species. The geographic range of Serracutisoma gnaspinii sp. nov. is compatible with the "Paraná" area of endemism, but with an unique distribution pattern compared to other endemic harvestmen species, which could indicate a new area of endemism also occupied by the primate Leontopithecus caissara Lorini & Persson, 1990.