Nauplius-The Journal of The Brazilian Crustacean Society

The present study provides a list of the freshwater crab species of the family Trichodactylidae recorded from the state of Maranhão, northeastern Brazil, along with information about their distribution. Eight streams were sampled with dip nets, sieves, gill nets, and drag nets. Four species were found: Dilocarcinus septemdentatus (Herbst, 1783), Goyazana castelnaui H. Milne Edwards, 1853, Sylviocarcinus pictus (H. Milne Edwards, 1853), and Valdivia serrata White, 1847. Our results increase the known distribution range of these species and add new records to more basins.

Despit being considered as a transitional zone between three biomes: the Amazon, Caatinga and Savanna (Ab' Saber, 1989), and having twelve hydrographic basins, few studies have focused on the freshwater fauna of the state of Maranhão. This is reflected in the little knowledge about richness and distribution of decapod crustacean fauna in this state. In this context, in the present study new surveys on the freshwater crabs fauna were made in order to close the gap of knowledge of this group for the state of Maranhão.
Sampling was carried out in eight streams located in Maranhão's Savanna region, including the streams: Itamacaoca, Prata, Feio, Canto Escuro, and Repouso, located in the municipality of Chapadinha; São José stream, in the municipality of Paulino Neves; Água Rica stream in the municipality of Tutóia; and Passagem do Canto stream located in the municipality of Barreirinhas. One sampling during the morning period in August through October 2014 and in March 2015 was made. Crabs were captured with dip nets, sieves, and drag nets with a sampling effort of 20 minutes along a determined stretch of 150 meters. The Chapadinha municipality comprises five of the eight sampled streams, located in the Munim river basin, within the savanna biome. The municipalities of Paulino Neves and Tutóia are located in the drainage of the Preguiças river basin (Fig. 1), also in the savanna biome.
Remarks. Three of the six specimens showed an asymmetric carapace in relation with the number of teeth. Two specimens showed six teeth on the right margin and five teeth on the left margin of the carapace, while one showed five teeth on the right margin and six on the left. According to Magalhães (2003a), this species presents variations on the carapace margin, having thin sharp teeth, which may be blunt or faded in larger specimens. The teeth of the carapace in the specimens found in this study can be considered thin, sharp and smaller in relations with those recorded by Lima Júnior et al. (2008) in Piauí. On the other hand, the teeth of individuals studied by Freita et al. (2013) in Pernambuco's semi-arid region, can be considered as blunt or faded.  (Magalhães, 2003a;Magalhães, 2003b;Alves et al., 2010;Silva et al., 2012;Lima et al. 2013 Distribution. Suriname, French Guyana, Brazil, and Peru (Barros and Pimentel, 2001;Magalhães 2003a;Magalhães and Turkay, 2008;Alves et al., 2010, Lima et al., 2013. Remarks. Three females and one male of the eleven specimens registered, presented asymmetric number of teeth on the carapace. Two females showed five teeth on the right margin and six teeth on the left margin, while the third female showed six teeth on the right margin and seven on the left margin. The male presented six teeth on the right margin and seven on the left margin of the carapace.  Distribution. Orinoco and Amazon river basins, as well as on coastal rivers of northern South America, in Venezuela, Colombia, Guyana, Suriname, Brazil, Peru, and Bolivia (Magalhães, 2002;2003a;Bernards, 2008;Alves et al., 2010;Lima et al., 2013).
This research adds new occurrence records for G. castelnaui, S. pictus, V. serrata, and D. septemdentatus. It is important to emphasize that in this study V. serrata was recorded for the first time in the Preguiças river basin, while D. septemdentatus and S. pictus were registered for the first time in the Munim river basin.
This research established new occurrence areas for freshwater crabs on the eastern region of the state of Maranhão. Furthermore, the number of hydrographic basins in the state of Maranhão with occurrence of freshwater crabs increased from three to five (Tab. 1). Thus, according to our results, the knowledge of freshwater crustaceans of the state of Maranhão is underestimated (Andrade et al., 2017). Therefore, a species catalog is urgently needed to understand species diversity in all hydrographic basins, considering possible consequences upon environmental modifications in several basins and sub-basins, such as pollution problems and deterioration of aquatic environments. The few studies available only provide sparse records, thus emphasizing the importance to survey the crustacean fauna in state of Maranhão. Moreover, other studies focusing on the comprehension of population and biological aspects in several basins are necessary to compare possible environmental damages.