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Opiliones are iconic arachnids with a Palaeozoic origin and a diversity that reflects ancient biogeographic patterns dating back at least to the times of Pangea. Owing to interest in harvestman diversity, evolution and biogeography, their relationships have been thoroughly studied using morphology and PCR-based Sanger approaches to infer their systematic relationships. More recently, two studies utilized transcriptomics-based phylogenomics to explore their basal relationships and diversification, but sampling was limiting for understanding deep evolutionary patterns, as they lacked good taxon representation at the family level. Here, we analysed a set of the 14 existing transcriptomes with 40 additional ones generated for this study, representing approximately 80% of the extant familial diversity in Opiliones. Our phylogenetic analyses, including a set of data matrices with different gene occupancy and evolutionary rates, and using a multitude of methods correcting for a diversity of factors affecting phylogenomic data matrices, provide a robust and stable Opiliones tree of life, where most families and higher taxa are precisely placed. Our dating analyses using alternative calibration points, methods and analytical parameters provide well-resolved old divergences, consistent with ancient regionalization in Pangea in some groups, and Pangean vicariance in others. The integration of state-of-the-art molecular techniques and analyses, together with the broadest taxonomic sampling to date presented in a phylogenomic study of harvestmen, provide new insights into harvestmen interrelationships, as well as an overview of the general biogeographic patterns of this ancient arthropod group.

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Mega hydroelectric dams have become one of the main drivers of habitat loss in tropical forests, converting large tracts of pristine forests into isolated forest islands. Understanding how biodiversity cope with landscape modification in these archipelagic landscapes is of paramount importance to assess the environmental consequences of dam infrastructure and propose mitigation actions for biodiversity conservation. In this context, harvestmen (Opiliones, Arachnida) comprise an excellent indicator taxon of habitat quality, given their high sensitivity to desiccation and microclimatic change. We investigate the effects of landscape change induced by a mega hydropower dam on forest harvestmen species richness, abundance and composition within the Balbina Hydroelectric Dam, Central Brazilian Amazon. We sampled 20 islands and 5 mainland continuous forests, relating our biological response variables to local, patch and landscape scale metrics. Although unexpectedly species richness was unaffected by any local, patch and landscape variables, species composition and abundance were differentially affected by a set of predictor variables at different scales. Forest cover and fallen woody stems were significant predictors of species composition, whereas vegetation density, forest cover, island area, abundance of palm trees, and fallen woody stems best explained harvestmen abundance. Our results indicate that both islands embedded within greater and lower amount of forest cover are important to ensure high diversity of harvestmen. We recommend retaining large forest habitat patches surrounded by a large amount of forest cover to minimise forest disturbance effects and enhance long‐term persistence of harvestmen sensitive species in large hydroelectric dams.

Abstract1. Arthropod diversity and non-flying arthropod food web are strongly influenced by habitat components related to plant architecture and habitat structural complexity. However, we still poorly understand the relationship between arthropod diversity and the vegetation structure at different spatial scales. Here, we examined how harvestmen assemblages are distributed across six local scale habitats (trees, dead trunks, palms, bushes, herbs and litter), and along three proxies of vegetation structure (number of palms, number of trees and litter depth) at mesoscale.2. We collected harvestmen using cryptic manual search in 30 permanent plots of 250 m at Reserva Ducke, Amazonas, Brazil. The 30 plots cover approximately 25 km2 of upland forests. At a local scale, harvestmen were most diverse and abundant on trees. The likely preference of trees by harvestmen may be related to the variety of local microhabitats offered by large trees. However, despite the strong link between number of harvestman species and individuals with large trees, only harvestmen assemblages composition were related with number of trees and with number of palms, at mesoscale.3. Harvestman richness and abundance were not related with any vegetation structure predictor at mesoscale. Therefore, areas of upland forest in the central Amazon with large trees and palms do not harbor more harvestman species nor individuals, but are suitable to maintain different harvestmen assemblages.

Cryptocellus icamiabas sp. nov. is described from an adult male from Amazonas state, Brazil. The new species is a member of the Amazonian foedus group, and is closest to Cryptocellus abaporu Bonaldo & Pinto-da-Rocha, 2003, Cryptocellus becki Platnick, 1977, and Cryptocellus simonis Hansen & Sorensen, 1904. The distribution pattern and morphology of the foedus group are briefly discussed.

The male, larva and nymphal stages of Cryptocellus iaci Tourinho, Lo Man-Hung & Bonaldo, 2010, a species previously known only from a single female, are described based on specimens from around the type locality, in an area of both Terra Firme forest and igapó (flooded forests), at the Jufari River, Roraima State, Brazil. The specimens were illustrated using live photography, stereomicroscopy, and scanning electron microscopy, allowing us to examine and describe the large diversity of tarsal sensilla and other integumental structures in Cryptocellus and to compare them to those of the previously studied Pseudocellus. Based on the male somatic characters Cryptocellus iaci is placed in the foedus species-group. Cryptocellus iaci has two sensilla of type 1 on the distal tarsomeres of legs III (DT III), while only one has been reported for Pseudocellus spp., suggesting a potential value in this type of character for systematic studies of the group.