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An assessment of the global freshwater crab diversity is presented. A total of 1,476 species in 14 families are currently known from all zoogeographical regions (except Antarctica), including 1,306 species in eight exclusively freshwater families (Pseudothelphusidae, Trichodactylidae, Potamonautidae, Deckeniidae, Platythelphusidae, Potamidae, Gecarcinucidae and Parathelphusidae). Estimates of true freshwater crab diversity including likely numbers of undescribed taxa suggest that the field remains largely in a ''discovery'' phase. Main ideas on the origins, diversification, and phylogeny of true freshwater crabs are briefly discussed. The economic importance of freshwater crabs is also highlighted.

A review of the species of freshwater prawns belonging to the genus Macrobrachium in Colombia is presented. According to the study, the genus Macrobrachium comprises 20 species for Colombia. The species Macrobrachium cortezi Rodríguez, 1982, M. ferreirai Kensley & Walker, 1982 and M. reyesi Pereira, 1986 are recorded for the first time in the country. Geographical species distributions are updated with basis on new material. Diagnoses, illustrations and a key for Colombian Macrobrachium species are included.

A revision of the cladistic analysis presented by Rodriguez and Pereira (1992) for the species of the genus Fredius Pretzmann, 1967 (Pseudothelphusidae), was carried out using additional species and new homologies to obtain a more robust cladogram. The tree obtained differs from the previous one in the clustering of species, but the area cladogram confirms a previous theory on the plausible evolution of the group in the Guianan lowlands of South America, between the Orinoco and the Amazon rivers. A new species is described from Colombia, extending considerably the range of the genus into the upper Amazon basin. A key to all species in the genus is given.

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A small collection of freshwater crabs from eastern Panamá revealed a new species of pseudothelphusid crab, Potamocarcinus darienensis n. sp., which is described and illustrated. The new species is characterized by an unusual arrangement of distal processes in the male first gonopod, in which the mesial lobe is folded in a latero-cephalic direction over the apex and the apex is broadened by a rounded protuberance in its caudo-lateral surface, the cephalic surface having a small, conical median cephalic process, and a large, prominent, subtriangular proximal cephalic process. New records of two little-known species described from eastern Panamá, Spirocarcinus garthi (Pretzmann, 1971) (Pseudothelphusidae) and Melocarcinus meekei (Pretzmann, 1968) (Trichodactylidae), are listed and the first gonopod of S. garthi is redescribed.

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