Sinopse opilionológica (Arachnida: Opiliones) do Estado do Ceará: estado da arte, desafios para a conservação e considerações biogeográficas no domínio da caatinga

Abstract

The opilionological richness recorded in the Brazilian semi-arid region corresponds to around 5% of the total species recorded in Brazil. However, there are still many sample gaps in several regions in the Caatinga Domain, including southwestern of Ceará. Although Ceará is entirely part of the Caatinga Domain, there are contrasting environments in the state, with a predominance of caatinga vegetation, deciduous shrub or tree vegetation and a semi-arid climate, but also with the presence of ‘brejos de altitude nordestinos’, which are enclaves of humid forests in the midst of the Sertaneja Depression, in addition to enclaves of savannas and the coastal strip. Investigating the opilionological fauna among the phytoecological units of Ceará can make it possible to understand whether or not there are divergences in species composition and reveal patterns of richness and endemism, in addition to documenting this group that is still little studied in the state. Our objective is: 1) Create a list of species occurring in Ceará; 2) Fill sampling gaps; 3) Evaluate the threats and the biogeographical distribution patterns of harvestmen occurring in Ceará and the level of endemism of the group. Data from literature, biological collections, fauna lists, online data generated by citizen science were collected and reviewed, in addition to conducting our own field surveys. We recorded 32 species of harvestmen in Ceará, of which 17 species are valid and already published, while another 15 species do not yet have a scientific description and have been grouped into morphospecies. These 32 species are distributed in 21 genera, of which five genera are not yet described, belonging to the families Cosmetidae (7 spp.), Escadabiidae (5 spp.), Gonyleptidae (8 spp.), Sclerosomatidae (3 spp.), Stygnidae (5 spp.) and Zalmoxidae (4 spp.). Seven species reported in the literature for Ceará do not actually occur in the state. The ‘brejos de altitude’ of Ceará (with 26 spp.) comprised the majority of records and represent areas of great richness, in contrast to the caatinga vegetation (with 8 spp.), which presented few species with a wider distribution. We raised threats to Ceará's opilionological fauna and highlighted that 8 species endemic to the state were recorded, inside caves and in conservation units. We evaluated the distribution patterns of harvestmen and, finally, partially filled the sampling gap in the region with new collections in the ‘RPPN Serra das Almas’. We indicate the current collection gaps in Ceará. This inventory contributes to better documentation of harvestmen in environments that are currently little studied and the mapping of records will provide an understanding of the biogeographical patterns of this region.