Potamonautes gorongosa, a new species of potamonautid freshwater crab (Decapoda, Brachyura) from Mozambique, southeastern Africa

A new species of the freshwater crab genus Potamonautes MacLeay, 1838, is described from Gorongosa National Park in Sofala Province, Mozambique, southern Africa. Potamonautes gorongosa, new species, is morphologically and phylogenetically distinct from the other species of Potamonautes found in Mozambique and nearby countries, and is most closely related to Potamonautes mutareensis Phiri and Daniels, 2013, from eastern Zimbabwe. e new species di ers from this species and its other congeners by a unique combination of morphological characters of the rst gonopod, the anterior sternum, third maxilliped, and the major cheliped. Illustrations of P. gorongosa new species are provided, and di erences with other species found in Mozambique and southeastern Africa are discussed.


INTRODUCTION
The freshwater crab fauna of several countries in southern Africa is poorly known despite a number of recent contributions (Reed and Cumberlidge, 2004;Cumberlidge and Tavares, 2006;Cumberlidge and Daniels, 2007;2009;Daniels and Bayliss, 2012;Phiri and Daniels, 2013;Daniels et al., 2014;2015) and some countries, such as Mozambique, have been overlooked until recently when it comes to biological inventories.It is therefore likely that there are still a number of species of freshwater crabs in Mozambique yet to be discovered, given its mountainous terrain and the lack of systematic survey work over the years (Cumberlidge, 1999;Cumberlidge and Daniels, 2009).e specimens reported on here from the Gorongosa National Park have a number of important characters that do not conform to the descriptions of any known African species (Chace, 1953;Bo , 1955;Cumberlidge, 1999;Reed andCumberlidge 2004, 2006), and proved to belong to a new species of Potamonautes MacLeay, 1838 (here named P. gorongosa new species) in the exclusively African freshwater crab family Potamonautidae Bo , 1970.e new species is described from a well-developed but still subadult male, and the taxonomically important characters of the gonopods, abdomen, mouthparts, carapace, sternum, and chelipeds are illustrated.Potamonautes gorongosa, new species, is compared with the eight other species of freshwater crabs that have been previously reported from Mozambique: Potamonautes bayonianus (Brito-Capello, 1873), Potamonautes bellarussus Daniels, Phiri andBayliss, 2014, Potamonautes calcaratus (Gordon, 1929), Potamonautes choloensis (Chace, 1953), Potamonautes namuliensis Daniels andBayliss, 2012, Potamonautes montivagus (Chace, 1953), Potamonautes obesus (A. Milne-Edwards, 1868), and Potamonautes sidneyi (Rathbun, 1904).Potamonautes gorongosa new species, is referred to as "Potamonautes sp.2" in Daniels et al. (2015, table 1, g. 2).e new species is also compared with super cially similar species found in neighboring countries that belong to the same phylogenetic lineage (such as Potamonautes mulanjeensis Daniels and Bayliss, 2012, from Zimbabwe, Potamonautes mutareensis Phiri andDaniels, 2013, from Malawi, andPotamonautes avusjo Daniels, Phiri andBayliss, 2014, from South Africa).e molecular phylogenetic study of Daniels et al. (2015, table 1, g. 2) found that the nine species of freshwater crabs reported from Mozambique (Tab. 1) belong to three separate clades (lineages) within the genus Potamonautes that diverged at di erent times in the past, and these relationships are also discussed here.
Dactylus of major cheliped slender, arched, closed ngers enclosing wide oval interspace; upper margin of dactylus of cheliped smooth; xed nger of propodus of major cheliped with 5 distinct, large teeth interspersed by smaller teeth; lower margin of propodus slightly indented (Fig. 2A, B); rst carpal tooth large, pointed; second carpal tooth less than half size of rst carpal tooth, pointed, followed by several small granules; distal meral tooth small, pointed; superior margins of merus of cheliped lined by series of small, pointed  teeth; superior surface of merus smooth, superior margin with carinae; outer face of merus smooth, lateral margin of inferior face of merus with very small teeth; inferior margin of ischium with small pointed teeth (Fig. 1A).Walking legs (p2-p5) normal length, inner margins of propodi p2-p5 smooth, dactyli of p2-p5 tapering to point, each bearing four rows of downwardpointing short, sharp spines (Fig. 1A).
Etymology.e new species is named for Gorongosa National Park in Mozambique, the only place that it is known to occur (so far).
Distribution.Potamonautes gorongosa, new species, is known from one locality in Gorongosa National Park in Mozambique. is is a 4,000 km 2 park at the southern end of the Ri Valley in central Mozambique, and includes Mount Gorongosa (1,863 m asl) where P. gorongosa was collected.e Gorongosa National Park dominates the Gorongosa District in Sofala Province of Mozambique.

New species of freshwater crab from Mozambique
Nauplius, 24: e2016029 Habitat. e freshwater crabs reported on in the present study were collected by the second author from Sofala Province in Mozambique, in highland and montane fresh waters where the vegetation type is predominantly savanna with fast-owing mountain streams and rivers.is narrow 450 km long area lies within the Eastern Zimbabwe Highlands ecoregion in southeastern Africa along the eastern border of Zimbabwe with Mozambique and includes the Nyanga and Chimanimani mountains whose rivers drain eastwards through Mozambique ( ieme et al., 2005;Abell et al., 2008).e known locality for P. gorongosa lies in the Zambezian lowveld freshwater ecoregion that comprises most of western and northern Mozambique and extends from south of the Zambezi delta in central Mozambique southwards to the Tugela River system in South Africa ( ieme et al., 2005;Abell et al., 2008). is species was collected with P. obesus a semi-terrestrial burrowing freshwater crab found in the coastal belt of eastern Africa from Kenya to Mozambique (Reed and Cumberlidge, 2004).e report of P. obesus from western Mozambique is a new record for this species in this part of the country.
Remarks.Afrotropical freshwater crabs undergo morphological changes as they grow and while most of this growth is isometric, some parts of their body (notably the major cheliped and the gonopods of males and pleopods of females) grow allometrically.Freshwater crabs start life as juveniles, then progress to subadults, and nally become reproductive adults a er passing through the pubertal moult (Cumberlidge, 1999).e specimen of P. gorongosa new species, is judged here to be a subadult following comparisons with congeneric species such as P. mulanjeensis, P. mutareensis, and P. avusjo (whose adults are between CW 30-34.8mm) (Daniels and Bayliss, 2012;Phiri and Daniels, 2013;Daniels et al., 2014). is indicates that although the specimen of the new species is a subadult, it is nevertheless of a body size that will soon undergo the pubertal moult. is distinction is important when considering the utility of taxonomic characters of freshwater crabs, although most of the morphological characters commonly used for taxonomy (such as those of the third maxilliped, thoracic sternum, mandible, the merus and carpus of the cheliped, and the number and size of the teeth on the cu ing edges of the cheliped ngers) undergo isometric growth and are not likely to be signi cantly di erent in subadults and adults.On the other hand, characters of the gonopods and major cheliped that grow allometrically are more developed in adults than in subadults.e subadult of the new species is well-developed and close to the pubertal moult, and so the gonopods would not be expected to develop a radically di erent form from those described here even a er the next moult.is is supported by the observations that the gonopods of P. gorongosa new species (Fig. 2C-F) are similar in most respects to those of the three genetically close species (P.mulanjeensis, P. mutareensis, and P. avusjo that are adult at CW 30.7 mm, 34.8 mm, and CW 34.8 mm respectively) (Daniels and Bayliss, 2012;Phiri and Daniels, 2013;Daniels et al., 2014).e same cannot be said of the ngers of the chelipeds of P. gorongosa new species, because although its major cheliped is enlarged in comparison with the minor cheliped (Fig. 2A, B), the major cheliped still lacks the dramatically curving dactylus and wide oval interspace enclosed by the closed ngers of adult males of P. mulanjeensis, P. mutareensis, and P. avusjo (see Daniels and Bayliss, 2012;Phiri and Daniels, 2013;Daniels et al., 2014).
Potamonautes gorongosa new species, is referred to as "Potamonautes sp.2" in Daniels et al. (2015, table 1, g. 2).Phylogenetically, P. gorongosa, new species, was found to be distinct from all other species in the large Afrotropical genus Potamonautes based on mtDNA and nDNA evidence, and it is most closely related to several species that share the same lineage ("Clade 3" in Daniels et al., 2015, g. 2) such as P. mutareensis (from Zimbabwe, misspelt as "P.mutariensis" in Daniels et al., 2015: table 1 and g. 2), P. mulanjeensis (from Malawi), and P. avusjo (from South Africa).e G1 terminal article of P. gorongosa new species closely resembles that of all three of these species (straight basally, medially curving outward at a 60° angle to the longitudinal axis of gonopod, and ending in a pointed and distinctly upturned tip) and it would be di cult to distinguish these taxa on this character alone.Fortunately, P. gorongosa new species, can be distinguished from P. mutareensis as follows (Phiri and Daniels, 2013): the vertical sulcus of the ischium of the third maxilliped is absent (vs.deep in P. mutareensis), the anterolateral margin of the carapace is smooth (vs.granulated in P. mutareensis), and s3/s4 is deep New species of freshwater crab from Mozambique Nauplius, 24: e2016029 at edges, faint in the middle, and does not meet the tip of the sternoabdominal cavity (vs.complete, deep and meeting the tip of the sternoabdominal cavity in P. mutareensis).Potamonautes gorongosa, new species, can be distinguished from P. mulanjeensis as follows (Daniels and Bayliss, 2012): the vertical sulcus of the ischium of the third maxilliped is absent (vs.distinct in P. mulanjeensis), and s3/s4 is incomplete and deep only at the margins (vs.complete and deep throughout in P. mulanjeensis).Potamonautes gorongosa, new species, can be distinguished from P. avusjo as follows (Daniels et al., 2014): the vertical sulcus of the ischium of the third maxilliped is absent (vs.distinct in P. avusjo) and s3/s4 is incomplete and deep only at the margins (vs.complete and deep throughout in P. avusjo).
Potamonautes gorongosa, new species, is easily distinguished from other species of freshwater crabs found in Mozambique (P.namuliensis, P. bellarussus, P. calcaratus, and P. obesus) both phylogenetically (Daniels et al., 2015, g. 2) because all are in di erent lineages from P. gorongosa, and morphologically (Reed and Cumberlidge, 2004;2006;Daniels and Bayliss, 2012;Daniels et al., 2014).For example, P. gorongosa, new species, can be distinguished from P. calcaratus and P. obesus from Mozambique as follows (Reed and Cumberlidge, 2004): the carapace is of medium height in the stream-living P. gorongosa (CH/FW = 1.1) (vs.highly vaulted in the semi-terrestrial burrowing crabs P. calcaratus and P. obesus, CH/FW = 1.2 and 1.3 respectively), and the dactylus of the major cheliped is slim and arched (vs.broadly a ened and high, an adaptation for burrowing in P. calcaratus and P. obesus), and the anterolateral margin of the carapace is smooth (vs.armed with a small sharp single spine in P. calcaratus and P. obesus).Potamonautes gorongosa, new species, can be distinguished from P. bellarussus as follows (Daniels et al., 2014): the anterolateral margin of the carapace is smooth (vs.granulated in P. bellarussus), the exorbital tooth is small (vs.large and prominent in P. bellarussus), and the carapace is of medium height (CH/FW = 1.1) (vs. a ened in P. bellarussus CH/FW = 0.97).Finally, P. gorongosa, new species, can be distinguished from P. namuliensis as follows (Daniels and Bayliss, 2012): thoracic sternal sulcus s3/s4 is incomplete and deep only at the margins (vs.complete and deep throughout in P. namuliensis), the postfrontal crest is incomplete but distinct (vs.very faint throughout in P. namuliensis), the dactylus and propodus of the cheliped are slightly arched with several large and medium sized teeth (vs.highly arched and lacking any conspicuous teeth in P. namuliensis), and the tip of the G1 terminal article is curved upward (vs. a straight uncurved tip in P. namuliensis).