Holotype: male, CL = 37 mm, ephemeral pan 200 m away from the western fence of False Bay Park (FB3), iSimangaliso Wetland Park (27°57'31.33"S, 32°21'42.15"E; elevation 62 m), 2 February 2015, R. Perissinotto, R.H. Taylor, D. Bilton, M.S. Bird, S.J. du Plooy and L. Clennell legit (ISAM A78908).

Allotype: female, CL = 27 mm, ephemeral pan, next to road leading from Dukandlovu campsite to False Bay Park entrance gate (FB5), 5 km south of Lister’s Point, iSimangaliso Wetland Park (28°0'51.70"S, 32°21'55.36"E; elevation 10 m), 1 February 2015, R. Perissinotto, R.H. Taylor, D. Bilton, M.S. Bird, S.J. du Plooy and L. Clennell legit (ISAM A78909).

Paratypes: one male, one female, collection data same as per holotype (NMMU); one male, ephemeral pan along the main road of False Bay Park (FB1), iSimangaliso Wetland Park (27°58'32.02"S, 32°21'51.62"E; elevation 42 m), 1 February 2015, R. Perissinotto, R.H. Taylor, D. Bilton, M.S. Bird, S.J. du Plooy, and L. Clennell legit (ISAM A78910); one male, ephemeral pan, collection data same as per allotype (ISAM A78911); two males, two females, ephemeral pan along the main road of False Bay Park (FB1), iSimangaliso Wetland Park (27°58'32.02"S, 32°21'51.62"E; elevation 42 m), 31 January 2015, R. Perissinotto, R.H. Taylor, D. Bilton, M.S. Bird, S.J. du Plooy, and L. Clennell legit (ISAM A78912); two females, collection data same as per holotype, 26 November 2013, R. Perissinotto, R.H. Taylor, N. Peer, N.A.F. Miranda, M.S. Bird, J.L. Raw and L. Clennell legit (NMMU); one male, one female, ephemeral pan near Sandy Point in False Bay Park (FB 6), iSimangaliso Wetland Park (27°58'36.0"S, 32°22'17.0"E; elevation 12 m), 25 November 2013, R. Perissinotto, R.H. Taylor, N. Peer, N.A.F. Miranda, M.S. Bird, J.L. Raw and L. Clennell legit (ISAM A78913); two males, ephemeral pan, collection data same as per allotype, 5 December 2012, R. Perissinotto, N.A.F. Miranda, N. Peer, J.L. Raw legit (ISAM A78914).

Main distinguishing features of P. isimangaliso from P. lividus Gouws, Stewart & Reavell, 2001 as follows: slightly granulated, horizontal anterolateral margin more rounded than in P. lividus; downward projection of postfrontal crest at exorbital edges; uniform colouration of dark purplish brown with lighter or orange coloured joints, cheliped tips and pereopods tips. Potamonautes isimangaliso is larger than P. lividus, with a maximum size of 37 mm CL recorded in males.

Carapace (Fig. 4a, c). Cephalothorax somewhat vaulted (CH/CL = 0.57), wide (CWW/CL = 1.49) and ovoid in general. Branchial region extremely rounded, forming a quarter of a circle with anterolateral margin. Anterior margin straight, lying on same horizontal plane as anterolateral margin; anterolateral margin slightly granulated. Urogastric grooves well-defined; cardiac and cervical grooves well-defined where attached to the urogastric groove, but then becoming poorly defined and shallow towards edge of carapace. Epigastric lobes well-defined above postfrontal crest by two indentations forked from midpoint of postfrontal crest. Postfrontal crest slightly granulated, curving forward medially. Postfrontal crest indistinct medially but pronounced posterior to orbital margins, curving prominently downwards at epibranchial region. Moderate presence of small exorbital teeth, but complete absence of epibranchial teeth. Flank of carapace smooth, with clear horizontal (epimeral) suture separating pterygostomial region from subhepatic and suborbital regions; vertical (pleural) groove dividing subhepatic region from suborbital region.

Figure 4. 

Potamonautes isimangaliso sp. n. male holotype CWW 55.1 mm (ISAM A78908). a dorsal view b ventral view and c cephalothorax, frontal aspect. Scale bar: 10 mm. Photos: Nasreen Peer.

Sternites (Fig. 4b). Sternites 1 and 2 fused; first sulcus absent as a result; second sulcus s2/s3 prominent, running completely across sternum; third sulcus s3/s4 projecting downwards medially towards abdominopelvic region. Sulci and episternal sulci thereafter well-defined but shallow.

Third maxillipeds (Figs 4c, 5e). Filling entire buccal frame except transversely oval respiratory openings at top lateral corners. Ischium slightly scabrous, with pronounced groove running vertically. Flagellum on exopod of third maxilliped fairly long, curving upward at distal ends.

Figure 5. 

Potamonautes isimangaliso sp. n. male holotype CWW 55.1 mm (ISAM A78908). a major cheliped b minor cheliped c right mandibular palp posterior view d right mandibular palp anterior view e 3^rd maxilliped f left gonopod 1 anterior view with enlarged terminal segment g left gonopod 1 posterior view with enlarged terminal segment h left gonopod 2 anterior view and i left gonopod 2 posterior view. Scale bars: 10 mm (a, b), 1 mm (c, d), 10 mm (e), 5 mm (f, g), 1 mm (h, i). Photos: Nasreen Peer.

Mandibular palp (Fig. 5c, d). Consisting of two segments; terminal segment undivided and smooth, with dense tuft of setae protruding from base; hirsute margins; light covering of setae on posterior surface; subterminal segment enlarged distally where it joins with terminal segment.

Pereopods (Figs 4a, b, 5a, b). General right-handedness and prominent inequality of chelae where CRDL/CLDL = 1.32. Dactyl of major chela moderately arched; large interspace formed in major cheliped when fingers are closed, long slim interspace formed by closing of fingers in minor cheliped. Twenty four cutting teeth present on the dactyl of major cheliped and 29 on dactyl of minor cheliped; 3 larger and more prominent than the rest. Propodus fairly inflated; right propodus larger (CRPL/CLPL = 1.41) and wider (CRPW/CLPW = 1.75) than left. Left pollex with 25 cutting teeth and right propodus with 18. Carpus on either side containing one prominent tooth followed by one smaller tooth. Meri strongly granulated around margins; slender pereopods (pereopod 2: ML/MW = 3.28; pereopods 5: ML/MW = 2.17), pereopod 3 is longest and pereopod 5 shortest; ventral margins of meri smooth; ventral margins of propodi slightly serrated; dorsal margins of meri and propodi bearing fine sharp bristles; dactyli serrated and ending in sharp points.

Pleon (Fig. 4b). First five segments broad and short, with segments 6 and 7 longer; segments 1–6 four sided, with triangular distally-rounded terminal segment (telson).

Pleopods (Fig. 5f, g, h, i). Gonopod 1 bearing short terminal segment only 0.23 times the length of the subterminal segment. Terminal segment curving slightly away from midline when viewed posteriorly. Gonopod widest at base, with both subterminal and terminal segments tapering and ending in sharp point. Inner lateral margin of subterminal segment irregular; outer lateral margin curving in a concave manner towards middle of gonopod; both margins hirsute. Groove extending almost through entire length of gonopod, visible on posterior surface, lined with setae. Distal margin of subterminal segment irregularly curved. Gonopod 2 consisting of two segments; terminal segment relatively long (0.47 times length of subterminal segment), very slim; subterminal segment wide at base, sharply becoming very narrow around 0.4 of length at which point narrow process forms, leading up to terminal segment. Small tuft of setae present on outer margin of base of subterminal segment. Gonopod 2 curved, moving outwards away from medial line of gonopod proximally, curving back towards medial line distally.

Variation. The major cheliped does not always display a pronounced interspace when fingers are closed. In juveniles and in the female allotype this was less prominent. The arching of chelipeds varies too, with some (particularly the minor chelipeds) bearing straight dactyli while others are fairly rounded. All collected specimens display a pronounced heterochely and all appear to be right-handed.

Colouration of carapace may vary between light brown, maroon, purplish-brown and almost black. Similarly, tips of dactyli may be either orange, bright yellow or a dull yellow.

Currently only known from the False Bay region of the iSimangaliso Wetland Park on the north-east coast of South Africa.

South Africa, KwaZulu-Natal, iSimangaliso Wetland Park, False Bay - Western Shores: Mpophomeni Pan (27°57'31.33"S, 32°21'42.15"E); Dukandlovu Pan (28°0'51.70"S, 32°21'55.36"E); Main Road Pan (27°58'32.02"S, 32°21'51.62"E); Sandy Point Pan (27°58'36.0"S, 32°22'17.0"E).

The species is named after the iSimangaliso Wetland Park, located in northern KwaZulu-Natal, where it is currently thought to be micro-endemic. This is significant as the iSimangaliso Wetland Park falls within the Maputaland centre of endemism (Smith et al. 2008), highlighting the importance of this park as a global biodiversity hotspot. The Park is a UNESCO World Heritage Site and contains three Ramsar Wetlands of International Importance.

Potamonautes isimangaliso sp. n. is easily distinguishable from most other Potamonautes spp. found in South Africa. Potamonautes dentatus Stewart, Coke & Cook, 1995, P. parvispina Stewart, 1997, P. unispinus Stewart & Cook, 1998, P. warreni Calman, 1918 and P. calcaratus (Gordon, 1929) all bear dentate anterolateral margins or epibranchial corners, while P. isimangaliso has a rounded epibranchial corner and mildly granular anterolateral margin.

Potamonautes perlatus (H. Milne Edwards, 1837), P. granularis Daniels, Stewart & Gibbons, 1998, P. sidneyi Rathbun, 1904, P. barbarai Phiri & Daniels, 2014 and P. barnardi Phiri & Daniels, 2014 all have sharply-defined scabrous or granular epibranchial corners and prominent postfrontal crest, while P. isimangaliso has a heavily rounded smooth epibranchial corner and poorly-defined postfrontal crest. Potamonautes parvicorpus Daniels, Stewart & Burmeister, 2001 also displays a finely granulated anterolateral margin and rounded epibranchial corners, but the resemblance to P. isimangaliso is superficial, as it differs in the indentation of its anterior margin where P. parvicorpus bears a slightly indented anterior margin while that of P. isimangaliso lies straight. Further differences are seen in locality as the habitat of P. parvicorpus is restricted to high mountain streams in the Western Cape (Daniels et al. 2001).

Potamonautes clarus Gouws, Stewart & Coke, 2000, P. depressus (Krauss, 1843), P. brincki (Bott, 1960), P. flavusjo Daniels, Phiri & Bayliss, 2014 and P. lividus Gouws, Stewart & Reavell, 2001 all have smooth anterolateral margins and rounded smooth epibranchial corners but bear differences compared to P. isimangaliso. One of the diagnostic characters of P. depressus is the dorsally flattened carapace, where CL/CH = 2.3–2.6. Potamonautes isimangaliso has a more vaulted carapace with a CL/CH ratio of 1.6–1.8. Potamonautes brincki and P. clarus are smaller crabs (max CL = 27 mm in males for both species), preferring fast-flowing mountain stream habitats. Potamonautes flavusjo is ecologically distinct from P. isimangaliso and can be found in the Mpumalanga Highveld. In addition to this, the species is smaller and has flattened chelipeds, not adapted for burrowing (Daniels et al. 2014). Light yellow chelipeds and ventral surfaces of pereopods characterise P. flavusjo.

Potamonautes lividus shares a similar distribution, outward appearance and preference for air-breathing with P. isimangaliso. However various differences exist between the two species.The level and angle of anterolateral margin differ, where P. isimangaliso bears an anterolateral margin lying on the same horizontal plane as the anterior margin. Conversely, P. lividus has an anterolateral margin which angles downward to join the anterior margin and thus sits higher than the anterior margin. The downward angle of postfrontal crest at exorbital edges is seen in P. isimangaliso but not in P. lividus. Carapace flatness is indicated by the CL/CH ratio which equates to 1.5 for P. lividus and 1.8 for P. isimangaliso holotypes. The maximum size (37 mm CL in P. isimangaliso and 25.5 mm CL in P. lividus), colouration (dark blue carapace with bright orange chelipeds in P. lividus and dark brown/purple carapace with brown or dull yellow cheliped in P. isimangaliso), inflation of chela with gap between propodus and dactyl (dactyl of P. lividus is more arched than that of P. isimangaliso) and the number of poorly-developed teeth on carpus (P. lividus containing one prominent and three rudimentary teeth; P. isimangaliso containing one prominent and one rudimentary tooth) further distinguish the two species. Gonopods of both species are very similar with the only difference being the tuft of setae found at the base of pleopod 2 in P. isimangaliso. Specimens resembling P. lividus were found in the Dwesa Forest, Eastern Cape and appear to be genetically nearly identical to P. lividus (Daniels et al. 2014). This further substantiates the genetic distinctiveness of P. isimangaliso. The smallest mature male of P. isimangaliso recorded had a CL of 13.2 mm whilst all females recorded were mature (min CL = 18 mm).

Preliminary sequence data for two mitochondrial gene regions (16S: GenBank accession number KR137640; COI: KR137642) generated from a representative of the new species, using approaches described elsewhere (Daniels et al. 2002; Phiri and Daniels 2014; G. Gouws unpubl.), were notably divergent (7.3% and 7.9%, respectively) from published 16S (AY042248; Daniels et al. 2002) and COI (AF510879; Daniels et al. 2002) sequences of Potamonautes lividus from KwaZulu-Natal.

Potamonautes isimangaliso sp. n. inhabits freshwater ephemeral pans (maximum salinity recorded: 0.75) which fill up with fresh, oxygen-deprived water after rainfall events, mainly during the summer wet season. These pans are located along the western shores of False Bay, Lake St Lucia (Fig. 6a–d) in clearings of the sand forest biome of False Bay and are generally partially shaded. Potamonautes isimangaliso and P. lividus are found in close proximity although P. lividus has not been found in False Bay Park and P. isimangaliso has not been found outside of the park. Furthermore, a difference in habitat type between P. isimangaliso and P. lividus Gouws, Stewart & Reavell, 2001 is seen, where the latter is known to inhabit burrows well above the surface water line in Ficus and Barringtonia swamps (Gouws et al. 2001), while the new species was found in close association with ephemeral pans in sand forest habitat with burrows extending below the surface waterline. Vegetation types include the dominant canopy species Cleisthantus schlechteri, Hymenocardia ulmoides, Psydrax fragrantissima, Croton pseudopulchellus and Drypetes arguta (Kirkwood & Midgley, 1999), as well as various Acacia spp. (Moll 1980). Grass species such as Paspalum vaginatum and Eleochoris sp. are also closely associated with this environment (Moll 1980). Aquatic plants associated with the ephemeral pans include the reed Typha capensis, the sedge Juncus kraussii, the mangrove fern Acrostichum aureum and the duckweed Lemna sp. (Howard-Williams 1980).

Figure 6. 

Sampling localities of Potamonautes isimangaliso sp. n.: a Main Road Pan (FB1) b Mpophomeni Pan (FB3) c Dukandlovu Pan (FB5) and d Sandy Point Pan (FB6), completely dry during Feb 2015. Photos: a–c Lynette Clennell; d Nasreen Peer.

Potamonautes isimangaliso adults form burrows on the banks of these pans (Fig. 7a), while juveniles are found either in burrows or free-crawling in shallow water (2–50 cm). The species lives sympatrically with P. sidneyi but is separated by habitat type, with P. sidneyi inhabiting flowing streams and able to withstand higher salinities of up to 9 (18 May 2013, Mpophomeni Stream, 27°57'7.17"S, 32°22'37.21"E). Oxygen levels in the pans inhabited by P. isimangaliso are quite low compared to flowing streams (Table 2).

Figure 7. 

A Burrows of Potamonautes isimangaliso sp. n. are typically found on the banks of ephemeral pans and are even maintained when pans are completely dry B Potamonautes isimangaliso sp. n. in its natural habitat. Photos: Lynette Clennell.

Although the species appears to be more closely associated with water than its morphologically closest congener, P. lividus (Gouws et al. 2001), the low levels of oxygen characteristic of the pans along with the ephemeral nature of the waterbodies indicate a greater affinity for a terrestrial lifestyle, as it may be more effective to obtain oxygen through air-breathing. This has been recorded previously in various African freshwater brachyuran genera and a high-vaulted carapace may be indicative of this change, where periods of dryness favour the evolution of burrowing semi-terrestrial, air-breathing tendencies (Cumberlidge 1999; Cumberlidge 2009). Specimens of P. isimangaliso have been observed in deep burrows (30–50 cm) around desiccated pools. Because the rainy season in this area is generally restricted to the period November-April (late Austral spring to early Autumn), much of the population hibernates deep in the mud, where traces of moisture persist throughout the dry season. Crabs return to the surface only after major rainfall events have filled up the ephemeral pools. The summer of 2014–2015 had been particularly dry in the area, with substantial rain falling in the False Bay area starting only in the middle of January (69 mm during 15–17 Jan, 54 mm during 28–30 Jan 2015; False Bay Park Meteo Station). Numerous adult and sub-adult crabs were observed from 31 Jan to 3 Feb in the newly filled ephemeral pools but hardly any young juvenile, indicating that the previous drought conditions had not allowed spawning to happen yet.

The feeding ecology of the species is largely unknown, although Potamonautes crabs are generally thought to shift from a diet of aquatic invertebrates to a more herbivorous or opportunistic diet with age (Hill and O’Keeffe 1992). The chelar dentition is serrate and the larger crusher chela lacks rounded or molariform occlusive geometry in the proximal region, probably due to wearing down over time. The dentition of the chela is indicative of an opportunistic omnivorous diet (Yamada and Boulding 1998).