New records of Macrobrachium Spence Bate , 1868 ( Decapoda , Palaemonidae ) from the northern coast of Brazil

Among the species belonging to the genus Macrobrachium Spence Bate, 1868, M. carcinus (Linnaeus, 1758) and M. olfersii (Wiegmann, 1836) are geographically widespread in the western Atlantic from the Gulf Coast to southern Brazil. We describe the current geographic distribution of M. carcinus and M. olfersii and include records of these species in the state of Maranhão, Brazil.


Methods
Samples of Macrobrachium species were collected from 20 to 21 November 2014 in São José and Água Rica streams, in the municipalities of Paulino Neves and Tutóia, Maranhão state.These streams are part of the drainage basin of the Rio Preguiças and lie within the savanna biome (IBGE 2010, NUGEO/UEMA 2011).
Dip nets and sieves were used around the margins of the streams and in marginal vegetation for a 20-min period over a 150 m stretch.Collected specimens were fixed in a 10% formaldehyde solution and preserved in 70% alcohol.In the laboratory, specimens were identified by using taxonomic keys (Holthuis 1952, García-Dávila and Magalhães 2003, Melo 2003, Sampaio et al. 2009), measured, and sexed.
The specimens total length was measured (CT, mea-

NOTES ON GEOGRAPHIC DISTRIBUTION
Observations.The size of male specimens was between 17.96 and 60.18 mm; females 15.12 and 41.93 mm (CT), weighing between 0.046 and 2.386 g for males and 0.0292 and 0,655 g for females.Bowles et al. (2000) recorded the largest male 90 mm long and ovigerous females between 30 and 65 mm, whereas Ammar et al. (2001) found males from 20.10 to 93.0 mm, females ranging from 23 to 58.20 mm, and ovigerous females 21.20 to 60.0 mm.Mossolin and Bueno (2002) recorded smaller sizes than previous literature, at 57.0 mm for the largest female and 81.93 mm for the largest male.In this study, sizes were smaller than found by Bowles et al. (2000), Ammar et al. (2001), and Mossolin and Bueno (2002).
Macrobrachium olfersii are found in submerged vegetation along the river banks, and with either a rocky and sandy substrate (Ammar et al. 2001, Mossolin and Bueno 2002, Melo 2003).Samples of M. olfersii from this study  were recorded in streams with marginal vegetation, sandy substrate, organic material and banks having leaves and roots.(Linnaeus, 1758) Figures 2, 3 Observations.This species occurs in the coastal basins and usually preferred pools with reduced water flow, occurring mainly in the middle to lower sections (Mejía-Ortiz 2001, Melo andCoelho 2008), although Mejía-Ortiz (2010) recorded species at altitudes varying from 1100 to 200 m.In this study, the species was records in streams with marginal vegetation, silt substrate, and organic material and roots.(Wiegmann, 1836) in the Neotropical regional (Table 1).In image c, there is a new occurrence of Macrobrachium carcinus (star) and in image d, the new occurrence of Macrobrachium olfersii (yellow triangle).

Discussion
Freshwater shrimp are important biotic components of the ecosystem (Lima et al. 2014), acting as herbivores, scavengers, predators, or prey of other animals (Ligeiro et al. 2014).They have the capacity to mitigate effects of catfish on periphyton and sediments (Scott et al. 2012), possess the symbiotic cleaning function (Garrone-Neto et al. 2014) ,and they are bioindicators of aquatic contamination (Nazari et al. 2003).
Macrobrachium olfersii is a small crepuscular species with continuous reproduction (Ammar et al. 2001, Mossolin and Bueno 2002, Melo 2003).Mossolin and Bueno (2002) observed that the species prefers warm waters than the other species recorded in this study and are greater in numbers during months with higher temperatures.Macrobrachium olfersii shows high sexual dimorphism in the second pair of pereopods between the left and right, in terms of unequal size and robustness in males, while in females the pereopods are less robust and equal (Mossolin and Bueno 2003).Cheliped growth occurs gradually, a distinguishing factor in the juvenile to the adult phases, in addition to be the main characteristic for taxonomic identification (Melo 2003, Mossolin andBueno 2003).
Popularly known as pitu, it is considered one of the largest of the freshwater shrimp on the east coast of the Americas (Lara and Wehrtmann 2009).Macrobrachium carcinus is included in the Red List of endangered invertebrate species in Brazil (Melo and Coelho 2008).The threats are mainly overfishing, habitat destruction, pollution, and construction of hydroelectric dams (Bowles 2000, Bauer 2011).Dams act as barriers that prevent the larvae of M. olfersii from migrating upstream in rivers.Planktonic marine larvae of this species are usually widespread because of currents (Bauer 2011), and the connectivity between marine and freshwater environments provide favorable conditions for reproduction.Therefore, disturbances in these habitats can affect species survival.
Fifty-five M. olfersii, but only 1 M. carcinus, were collected.This single collected specimen of M. carcinus is probably due to the difficulty in collecting this species in gill and dip nets, because cove traps are generally used for this shrimp (Rocha 2010).The number of freshwater shrimp species in the state of Maranhão is now increased from 4 to 6 species.
The freshwater crustaceans of the state of Maranhão are underestimated.A catalog of species is urgently needed to comprehend species diversity.In future research, information on collection methodology, including the type of traps, are needed in order to obtain a more effective qualitative and quantitative survey of the local crustacean fauna.Mantelatto et al. (2016)

Figure 3 .
Figure 3. Geographic distribution of M. carcinus (Linnaeus, 1758) and M. olfersii(Wiegmann, 1836)  in the Neotropical regional (Table1).In image c, there is a new occurrence of Macrobrachium carcinus (star) and in image d, the new occurrence of Macrobrachium olfersii (yellow triangle).

Table 1 .
highlighted the need for new checklists and better knowledge of palaemonidean shrimp life histories.Geographic distribution of Macrobrachium carcinus (Linnaeus, 1758) and M. olfersii(Wiegmann, 1836)in the Neotropical region.