Just a brief Taxon of the Week entry today because unfortunately I don't have a lot of info available on this taxon. The name Collonychium was recently revived from taxonomic limbo by Kury (2003) for two species of gonyleptid harvestmen found in south-east Brazil. Collonychium bicuspidatum is found in the provinces of Rio de Janeiro, São Paulo and Paraná while C. perlatum is found in Espírito Santo and Minas Gerais. Collonychium bicuspidatum had previously been included in the genus Paragonyleptes, of which it is the type species, before Kury (2003) recognised the type specimen of Collonychium bicuspidatum as a juvenile female of Paragonyleptes bicuspidatus (despite having the same species names, these two were originally described as separate species). A number of other southern Brazilian harvestman species had been assigned to Paragonyleptes, mostly by the famed creator of artificial classifications Carl-Friedrich Roewer and Cândido Firmino de Mello-Leitão (who, if anything, out-Roewered Roewer). These species were mostly listed by Kury (2003) as Gonyleptinae incertae sedis so they may or may not be Collonychium species.
I'm not entirely sure what's happening in this photo, again by Abel & Ana. Gonyleptids such as Collonychium have very powerful posterior-directed hindlegs, often with large spines pointing inwards on the retrolateral side (they're not as prominent in this individual, but in other species they may be very scary indeed). I think the individual in the photo above may be executing a handstand in order to bring the hindlegs into a better position to scissor with them at its intimidator (in this case, the photographer).
Kury, A. B. 2003. Annotated catalogue of the Laniatores of the New World (Arachnida, Opiliones). Revista Ibérica de Aracnología, volumen especial monográfico 1: 1-337.