The Neotropical region has its own distinctly recognizable freshwater crab fauna, with no species occurring in other parts of the world. The Neotropical freshwater crab fauna is not uniformly distributed and species and genus composition changes from country to country (Table 2, Figs 1, 2). The global distributions of all species of the Pseudothelphusidae and Trichodactylidae based on all known localities are shown in figures 1 and 2. The Neotropical freshwater crab fauna today (49 genera, 311 species, 2 families) easily exceeds that of the entire Afrotropical region (18 genera, 145 species, 2 families), but is significantly less diverse than the Palaearctic-Oriental-Australasian region (147 genera, 850 species, 2 families) (Cumberlidge et al. 2009; present work).

The Neotropical freshwater crab fauna, which represent 20–22% of the world’s freshwater crab species diversity (Ng et al. 2008, Yeo et al. 2008, Cumberlidge et al. 2009), is dominated by the highly diverse pseudothelphusids (34 genera, 264 species). Pseudothelphusids are found in 26 out of the 31 countries and reach their highest species richness in South America (Table 2). Pseudothelphusids are found throughout the warmer parts of the Neotropics from Mexico to Central America and the Andes (Venezuela, Colombia, Ecuador, and Peru), and in the Guyanian Shield and Central Brazilian Shield in the Amazon basin (Fig. 1, Table 2). The majority of pseudothelphusid species live at altitudes greater than 400 m above sea level, with a few Andean species reaching up to 3000 m (Campos 2005).

This family comprises two subfamilies, Epilobocerinae and Pseudothelphusinae (Ng et al. 2008). The Epilobocerinae consists of only 9 species in 2 genera (Epilobocera, Neoepilobocera) that are all endemic to the larger islands of the Greater Antilles (Cuba, Haiti, Dominican Republic, Puerto Rico, and St. Croix). The vast majority of pseudothelphusids are in the subfamily Pseudothelphusinae assigned to five Tribes: Pseudothelphusini (Mexico), Potamocarcinini (Central America and Mexico), Hypolobocerini (from Venezuela to Peru, plus Central America, and Mexico), Strengerianini (Colombia and Venezuela), and Kingsleyini (the Lesser Antilles, Venezuela, Colombia, and northern Brazil). The eastern limits of the Pseudothelphusidae in the Amazon basin is in Ceará State, Brazil, while their southwestern limit in the Amazon basin is marked by the watershed of the Ucayali River, south of which there are no species of pseudothelphusids (Rodríguez and Magalhães 2005).

The Trichodactylidae is the smallest of all freshwater crab families (15 genera, 47 species) and represents only 4% of the world’s freshwater crab diversity. Despite this, the family is widely distributed and has representatives in 16 countries, most of which are in South America (Table 2) (Rodríguez 1992, Ng et al. 2008, Yeo et al. 2008, Cumberlidge et al. 2009). The vast majority of trichodactylid species are found below 100 m above sea level in the Magdalena river basin and Lake Maracaibo in Colombia and Venezuela, in the coastal lowlands of the Guyanas and Brazil, and in the lowland river basins of the Amazon, Orinoco, Paraguay, and Parana. A few species of trichodactylids reach up to 900 m above sea level in the Andes foothills (Campos 2005). Countries with trichodactylids include Colombia, Venezuela, French Guiana, Guyana, Suriname, Brazil, Ecuador, Peru, Bolivia, Paraguay, Uruguay, and Argentina (Fig. 2, Table 2). Outside of South America there are four trichodactylid species in Veracruz, Tabasco, Oaxaca, and Chiapas in Mexico (Avotrichodactylus constrictus, Avotrichodactylus oaxensis, Rodriguezia mensabak, and Rodriguezia villalobosi) (Magalhães and Türkay 2012); one species (Trichodactylus quinquedentatus) from Colombia and Nicaragua (Smalley and Rodríguez 1972), and one species (Poppiana dentata) from Trinidad (which is also found on the neighboring mainland in Venezuela, Suriname, Guyana, and French Guiana, and in Nicaragua) (Magalhães and Türkay 2008a). The Trichodactylidae includes two subfamilies: the Trichodactylinae, with 3 genera, two from Mexico (Avotrichodactylus and Rodriguezia) and one from South and Central America (Trichodactylus); and the Dilocarcininae, with 9 genera that are found throughout South America (Rodríguez 1992, Magalhães and Türkay 1996a, b, c, 2008a, b). Interestingly, this classification (Ng et al. 2008) groups together at the subfamily level the four disjunct species of trichodactylids found in Mexico with the genus Trichodactylus that includes species from the Magdalena basin and Amazon slopes in Colombia, a species from Nicaragua and Colombia, species from the Atlantic coastal river systems of southeastern Brazil, and species from the Paraguay and Parana basins in southern Brazil and Argentina.

Colombia stands out as the most diverse and the most species rich part of the region (21 genera, 102 species, 2 families) (Table 2) with biodiversity hotspots located in forested mountainous regions where deep valleys and a complex topographical relief are favorable for genetic isolation and allopatric speciation. The pseudothelphusid fauna of Colombia comprises 13 genera and 88 species in one subfamily (Pseudothelphusinae) and four tribes (Hypolobocerini, Strengerianini, Kingsleyini, and Potamocarcinini). There are distinct northern and southern components of pseudothelphusid distribution in Colombia, with the dividing line coinciding with the watersheds of the San Juan, Cauca, and Magdalena river basins. The southern component of this fauna is dominated by Hypolobocera, Lindacatalina, and Moritschus and extends from southern Colombia into Ecuador and Peru, and also includes species from southeast Colombia and the Amazonian and Pacific slopes of Ecuador. The trichodactylid fauna of Colombia comprises 8 genera, 14 species in two subfamilies: Trichodactylinae (one genus) and Dilocarcininae (7 genera).

The next most species-rich country is Mexico (17 genera, 67 species, 2 families) (Table 2) with a freshwater crab fauna dominated by pseudothelphusids with 15 genera, and 63 species in one subfamily (Pseudothelphusinae) and three tribes (Pseudothelphusini, Potamocarcinini, and Hypolobocerini). Mexico’s trichodactylid fauna is much smaller and comprises just 4 species in 2 genera all in the subfamily Trichodactylinae. Freshwater crab diversity in Mexico is highest in the Isthmus of Tehuantepec and Chiapas State, possibly because this is where species from three pseudothelphusid tribes overlap with species of trichodactylids (Villalobos and Alvarez 2010).

Brazil is the third most species-rich Neotropical country (16 genera, 50 species, 2 families) with a fauna that is dominated by trichodactylids (10 genera, 31 species, 2 subfamilies), and fewer pseudothelphusids (6 genera, 19 species, all Pseudothelphusinae, Kingsleyini). Venezuela is the fourth most species-rich Neotropical country (18 genera, 44 species, 2 families), made up of 11 genera and 35 species of pseudothelphusids (all Pseudothelphusinae, in three tribes, Hypolobocerini, Kingsleyini, and Strengerianini), and 7 genera and 9 species of trichodactylids (all Dilocarcininae).

The freshwater crab fauna of Ecuador (7 genera, 26 species, 2 families) includes 3 genera and 21 species of pseudothelphusids (all Pseudothelphusinae, Hypolobocerini), and 4 genera and 5 species of trichodactylids (all Dilocarcininae). Finally, Peru (11 genera, 22 species, 2 families) has a fauna dominated by trichodactylids (14 species and 8 genera, in 2 subfamilies Dilocarcininae and Trichodactylinae), with a smaller pseudothelphusid fauna consisting of 8 species and 2 genera (all Pseudothelphusinae in 2 tribes Kingsleyini and Hypolobocerini). Freshwater crabs of both families are completely absent from Chile. Despite warm subtropical climates freshwater crabs are absent in many islands of the Caribbean including Jamaica, The Cayman Islands, The Bahamas, Grenada, Antigua, and Anguilla.

When distribution patterns are considered at the genus level (Table 2) the taxonomic diversity of Neotropical freshwater crabs is again by far the highest in Colombia (21 genera), Venezuela (18 genera), Mexico (17 genera), Brazil (16 genera), and Peru (11 genera). Diversity is lower in Ecuador (7 genera), Guyana, Suriname, Bolivia, Paraguay, French Guiana, Nicaragua, and Guatemala (6 genera), and in Argentina and Panama (5 genera) (Table 2). Costa Rica, El Salvador and Belize each have 4 genera, Trinidad and Tobago has 3 genera, Honduras and Cuba each have 2 genera, while Uruguay and the other islands of the Greater and Lesser Antilles each have 1 genus.

Thirteen (out of 34) pseudothelphusid freshwater crab genera and 28 (out of 283) species have a wide distribution that easily exceeds 20,000 km² and includes more than one country. Notably, Fredius reflexifrons is found in six countries (Brazil, French Guiana, Guyana, Peru, Suriname, Venezuela), Potamocarcinus magnus is found in five countries (Mexico, Guatemala, Honduras, El Salvador, Costa Rica), and Kingsleya latifrons (Guyana, French Guiana, Suriname, Brazil) and Raddaus bocourti (Mexico, Belize, Guatemala, El Salvador) are found in four countries. Other widespread species found in three countries include Potamocarcinus armatus (Mexico, Guatemala, Nicaragua), Potamocarcinus richmondi (Nicaragua, Costa Rica, Panama), Fredius denticulatus (Brazil, French Guiana, Suriname) and Fredius fittkaui (Venezuela, Guyana, Brazil), and Prionothelphusa eliasi (Brazil, Colombia and Venezuela). Finally, 17 widespread species are found in two countries: Rodriguezus garmani (Trinidad and Tobago, Venezuela), Fredius beccarii (Guyana, Venezuela), Zilchia zilchi (El Salvador, Honduras), Hypolobocera caputii and Moritschus henrici (both Ecuador, Peru), Ptychophallus exilipes (Costa Rica, Panama), Hypolobocera bouvieri angulata, Orthothelphusa holthuisi (Colombia, Venezuela), and Hypolobocera exuca, Lindacatalina latipenis, Lindacatalina orientalis, and Lindacatalina sumacensis (all Colombia, Ecuador), Fredius estevisi and Fredius platyacanthus (Brazil, Venezuela), Kingsleya siolii (Brazil, Suriname), Zilchia aspoekorum (Belize, Mexico), and Raddaus tuberculatus (Guatemala, Mexico).

The majority of pseudothelphusids (22 species) that have a widespread distribution exceeding 20,000 km² are assessed as Least Concern. However, there are some species with a small distributional range that spans the border between two neighboring countries that are assessed as either Vulnerable: Hypolobocera exuca (Colombia, Ecuador), Kingsleya siolii (Brazil, Suriname) and Zilchia aspoekorum (Belize, Mexico), or Data Deficient: Fredius platyacanthus (Brazil, Venezuela), Lindacatalina latipenis and Lindacatalina sumacensis (both Colombia, Ecuador), Orthothelphusa holthuisi (Colombia, Venezuela), and Ptychophallus exilipes (Costa Rica, Panama).

Some 8 out of 15 trichodactylid freshwater crab genera and 20 out of 47 species have a wide distributional range exceeding 20,000 km² that spans more than one country: all are assessed as Least Concern. Notably, Valdivia serrata is found in nine countries (Bolivia, Brazil, Colombia, Ecuador, Peru, Venezuela, Guyana, Suriname, French Guiana), Poppiana dentata in eight countries (Brazil, Colombia, French Guiana, Guyana, Nicaragua, Suriname, Trinidad and Tobago, Venezuela), and Sylviocarcinus pictus in seven countries (Colombia, Brazil, Bolivia, Peru, Argentina, French Guiana, Guyana). Dilocarcinus pagei is found in six countries (Argentina, Brazil, Bolivia, Colombia, Paraguay, Peru), and Sylviocarcinus devillei and Moreirocarcinus emarginatus are both found in 5 countries (Bolivia, Brazil, Colombia, Ecuador, and Peru; and Brazil, Colombia, Ecuador, Peru, and Venezuela respectively). Four species are found in four countries: Trichodactylus kensleyi (in Argentina, Brazil, Paraguay and Uruguay) and Poppiana argentiniana, Valdivia camerani, and Trichodactylus borellianus (in Argentina, Bolivia, Brazil, and Paraguay). Seven species are found in three countries (Rotundovaldivia latidens, Sylviocarcinus maldonadoensis, Sylviocarcinus australis, Trichodactylus faxoni, Trichodactylus panoplus, Valdivia cururuensis and Zilchiopsis oronensis), four species are found in two countries (Bottiella niceforei, Bottiella cucutensis, Forsteria venezuelensis, Trichodactylus quinquedentatus), and three species are found in one country (Trichodactylus petropolitanus, Valdivia novemdentata, and Zilchiopsis collastinensis).

Freshwater crabs are found in all major habitat types in the Neotropics (Thieme et al. 2005; Abell et al. 2008) including rivers, rapids, swamps, lakes, caves, and mountain streams and species belonging to both families prefer warm-water habitats year round. The Pseudothelphusidae are typically found in small mountain streams above 400 m above sea level, which may in part reflect their ability to breathe air and live a semi-terrestrial existence. Pseudothelphusids reach their highest diversity in the rivers and streams that drain the highland areas of the cordilleras of Colombia and Ecuador. In contrast, trichodactylids are most abundant in the vast network of lowland rivers of South America that make up the Amazon, Orinoco, Paraguay, and Parana basins (Cumberlidge et al. 2009). Species diversity tends to be highest where vegetation cover is densest and water availability is highest, and there are fewer, or no species found in the more arid ecosystems and those with colder water temperatures. The pattern of the dominance of Pseudothelphusidae in Colombia, Venezuela, Ecuador, Peru, Mexico, Central America, and the Caribbean, and their absence in Bolivia, Uruguay, Paraguay, southern Argentina, and Chile probably reflects an origin somewhere in Colombia and Venezuela, from where they spread out north to Central America and Mexico, east to the Guyanas and Lesser Antilles, and south as far as Brazil and Peru (Rodríguez 1982, 1986).

Similarly the dominance of Trichodactylidae in the Amazon, Orinoco, Paraguay, and Parana River basins and their absence from Chile and from aquatic ecosystems at high altitudes in the Andes elsewhere in South America reflects their preference for an aquatic, rather than a semiterrestrial life (Rodríguez 1982, 1986). However, it is harder to explain the presence of trichodactylids in Central America, Mexico, and Trinidad in localities that lie well outside of the major river basins of the South American subcontinent (Rodríguez 1992).

Twenty-four species of neotropical freshwater crabs are found in caves (22 pseudothelphusids and two trichodactylids), and are either fully adapted to a life in caves, or are visitors to caves and have a distribution that also includes surface waters (Table 3). Twelve species of cave-dwelling freshwater crabs are from Mexico, five from Central America (Belize 1, Guatemala 3, and Costa Rica 1), two from the Caribbean (Cuba 1, Puerto Rico, and St. Croix 1), and five from South America (Colombia, 2 and Venezuela 3).

The majority of freshwater crab species found in Colombia (81%) are country endemics: 78 species of pseudothelphsids and 5 species of trichodactylids (Cumberlidge et al. 2009). The high degree of endemism in Colombia’s freshwater crab fauna at the species level (83 of 102 species, 81%) is also seen to a lesser extent at the genus level (9 of 21 genera, 43%), but not at the family level (neither of the two families are exclusively found in Colombia). Many of the Colombian endemics are found in the isolated mountain streams and in the middle stretches of rivers associated with rainforest (Campos 2005). Mexico’s freshwater crab fauna has the next highest number of country endemics (66 of 67 species, 97%) that is also seen at the genus level (13 of 17 genera, 76%), but not at the family level (neither of the two families are exclusively found in Mexico). Many of the Mexican endemics are found in the isolated mountain streams and in the middle stretches of rivers associated with the rainforests and caves (Villalobos and Alvarez 2010). All species of freshwater crabs found in Cuba and Hispaniola are island endemics.

The conservation status of the 298 species of freshwater crabs known from the Neotropical region in 2009 was evaluated against the IUCN (2003) Red List criteria (version 3.1) and is available on the Red List site (www.iucn.redlist.org). These results were summarized by Cumberlidge et al. (2009). The conservation status of species described since that work (Table 1) has not yet been assessed. Unfortunately, about half of all Neotropical freshwater crabs (148 species) are too poorly known to submit to the assessment protocols and are listed as Data Deficient, notably some 80% of the diverse Mexican fauna (Tables 5, 6). Of the remaining 150 species that could be assessed (belonging to 22 genera and 2 families) the majority (107 species) were found to be of Least Concern, and most of these species either live in rivers, marshy lowlands, or in mountain streams in the forested highlands (Cumberlidge et al. 2009). For the Pseudothelphusidae, 111 out of 251 species were assessed (140 species were data deficient), and of these, 72 species of Least Concern, 2 species were Critically Endangered, 3 species were Endangered Critically Endangered, 3 species were Endangered, and 33 species were Vulnerable (Tables 5, 6). For the Trichodactylidae, 39 out of 47 species were assessed (8 species were Data Deficient), and of these, 35 species were of Least Concern, one species was Endangered, and three were Vulnerable (Table 6). For both families combined, 42 of the 150 assessed species of Neotropical freshwater crabs (28%) were listed in one of three threatened categories, either as Critically Endangered (2 species), Endangered (4 species) or Vulnerable (36 species) (Table 7). One species was assessed as near threatened, and no species of Neotropical freshwater crabs was confirmed as Extinct or Extinct in the Wild. However, it should be noted that a species cannot be formally assessed as extinct until exhaustive surveys probing its disappearance have been carried out. Because conservation status could not be assigned to large numbers of Data Deficient species (148), the proportion of threatened species in Cumberlidge et al. (2009) (32%) is almost certainly an underestimation. This means that the number of threatened species could well increase should a Data Deficient species subsequently be assessed as threatened (Cumberlidge et al. 2009). Despite the large numbers of specimens available very little information is available on population levels and trends, except for a qualitative estimate (e.g., whether common or rare) based on the number of sites at which a species is present and its relative abundance at each site.

With only 42 out of 298 species of Neotropical freshwater crabs known in 2009 assessed as threatened with global extinction (Tables 5–7), the region’s largely endemic freshwater crab fauna (Table 4) does not appear at first sight to be in immediate trouble compared with other aquatic groups found in the same freshwater habitats (e.g., fish, molluscs, and dragonflies) (Collen et al. 2008). The 107 species of Neotropical freshwater crabs judged to be of Least Concern (35 species of trichodactylids, and 72 species of pseudothelphusids) have a wide distribution in rivers, lakes, highland streams and lowland wetlands, and appear to be tolerant of changes in land use that affect aquatic ecosystems.

Threats to Neotropical freshwater crabs include habitat destruction driven by increasing agriculture, the demands of increasing industrial development, and the alteration of fast flowing rivers for the creation of hydroelectric power (Cumberlidge et al. 2009). Even species assessed as Least Concern could suffer a catastrophic decline should there be abrupt changes in land development, hydrology, or pesticide-use regimes. Species with a narrow distribution are vulnerable to extreme population fragmentation and could suffer a rapid decline and even extinction in a relatively short time should dramatic changes in land-use affect their habitat. The 148 species of Neotropical freshwater crabs judged to be Data Deficient are mostly rare species, and their conservation status needs to be re-evaluated once more information comes to light. It is hoped that prioritizing species for conservation action through the Red List assessment process will lead to the development of conservation recovery plans for threatened species in the future.