I was recently sent the following photos by Gabriel Whiting asking if I was able to supply an ID:
He had photographed this animal at Itatiaia in the province of Rio de Janeiro in Brazil. The photos don't give a direct indication of its size but Gabriel told me that it was quite big (at least for a bug) and you can see a couple of other insects in the wider photo for comparison.
It's obviously a harvestman of the South American family Gonyleptidae. A photo of a similar individual in Kury & Pinto-da-Rocha (2007) led me to identify Gabriel's mystery opilionid as Acutisoma unicolor (a paper currently in press will apparently shift its genus allocation to Goniosoma). According to Kury (2003), Itatiaia happens to be the type and (so far) only recorded locality for this species and information specifically relating to this species seems to be thin on the ground.
Casting the net wider, Acutisoma unicolor belongs to the subfamily Goniosomatinae which is endemic to the Brazilian coastal region (Kury & Pinto-da-Rocha, 2007). As large, readily visible animals, goniosomatines have been subject to a reasonable amount of study, particularly in regard to reproduction. Males of at least some goniosomatines may maintain territories in which they may guard harems of up to five females. Fights over territory may be long and fierce with the main appendages used being the long filiform legs II and the powerfully armed legs IV (Machado & Macías-Ordóñez, 2007). Most goniosomatines observed to date lay their batches on eggs in gaps between rocks or on the walls of caves. The eggs are generally looked after by the females though males have been recorded watching over eggs laid in their territory whose mother has temporarily gone elsewhere (Buzatto & Machado, 2009). Newly hatched juveniles may also remain clustered around the female.
Buzatto, B., & G. Machado. 2009. Amphisexual care in Acutisoma proximum (Arachnida, Opiliones), a neotropical harvestman with exclusive maternal care. Insectes Sociaux 56 (1): 106-108.
Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachida, Opiliones). Revista Ibérica de Aracnología, special monographic volume 1: 1-337.
Kury, A. B., & R. Pinto-da-Rocha. 2007. Gonyleptidae Sundevall, 1833. In Harvestmen: The Biology of Opiliones (R. Pinto-da-Rocha, G. Machado & G. Giribet, eds) pp. 196-203. Harvard University Press: Cambridge (Massachusetts) and London.
Machado, G., & R. Macías-Ordóñez. 2007. Reproduction. In Harvestmen: The Biology of Opiliones (R. Pinto-da-Rocha, G. Machado & G. Giribet, eds) pp. 414-454. Harvard University Press: Cambridge (Massachusetts) and London.
17 hours ago in Variety of Life