Potamonautes amathole Peer & Gouws, 2023

Peer, Nasreen, Gouws, Gavin, Maliwa, Lazola, Barker, Nigel, Juby, Paul & Perissinotto, Renzo, 2023, Description of a new montane freshwater crab (Arthropoda, Malacostraca, Decapoda, Potamonautidae) from the Eastern Cape, South Africa, ZooKeys 1160, pp. 89-108 : 89

Potamonautes amathole Peer & Gouws sp. nov.

Type series.

Holotype: male, CL = 25.3 mm (Table 2 ), cascading stream in the Katberg State Forest (32°28'26.4"S, 26°40'05.9"E, elevation 1070 m), 25 October 2018, L. Maliwa, N. Miranda and N. Peer legit (MB-A094813). Allotype: female, CL = 24.9 mm (Table 2 ), collection details as per holotype (MB-A094814). Paratypes: (Table 2 ) collection details same as above, MB-A094815 (8 ♂, 4 ♀). Hogsback Arboretum, MB-A094816 (2 ♀), 32°35'25.2"S, 26°56'02.7"E, elevation 1235 m, 24 October 2018, L. Maliwa, N. Miranda and N. Peer legit. Madonna and Child Waterfall, Hogsback, MB-A094817 (1 ♂, 1 ♀); 32°36'24.4"S, 26°57'48.2"E, elevation 1092 m, 24 October 2018, L. Maliwa, N. Miranda and N. Peer legit.

Diagnosis.

Potamonautes amathole sp. nov. exhibits a smooth carapace, flank and epibranchial region, with a rounded anterolateral margin and a narrow posterior end. Postfrontal crest complete. Dactyl of major cheliped highly arched. Pereopod 4 is longest. Bi-lobed maxillary palp with no flange.

Description of holotype.

Carapace (Fig. 4 ). Cephalothorax ovoid, dorsally flattened, maximum height and width at anterior third (CH/CL = 0.5, CWW/CL = 1.47). Branchial region rounded. 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 urogastric groove, becoming poorly defined and shallow towards edge of carapace. Epigastric lobes well-defined by two indentations forked from midpoint of postfrontal crest. Postfrontal crest complete, straight, and distinct, curving down at epibranchial region, sloping backwards to join anterolateral margin. Exorbital teeth present. Epibranchial teeth absent. Carapace brown with orange-brown to purple-brown limbs when alive.

Sternites (Fig. 4b ). Sternites 1 and 2 fused, no sulcus. Second sulcus (s2/s3) prominent across sternum and third sulcus (s3/s4) complete, deep, projecting down medially towards abdomen.

Third maxilliped (Figs 4c , 5e ). Filling entire buccal frame except oval respiratory openings at top lateral corners. Ischium slightly scabrous, absence of vertical groove. Flagellum on exopod of third maxilliped curving upwards at distal ends.

Mandibular palp (Fig. 5c, d ). Consists of two segments. Terminal segment undivided, with dense tuft of setae on posterior proximal surface, margins hirsute. Subterminal segment short, thickened distally, almost round in appearance.

Pereopods (Figs 4a, c , 5a, b ). General right-handedness. Inequality of chelae (CRDL/CLDL = 1.41). Dactyl of major chela highly arched, large interspace formed in major cheliped when fingers closed, slim interspace formed when minor cheliped closed. Propodus fairly slim (CRPW/CRPL = 0.41), exhibiting 17 cutting teeth on major dactyl and 15 cutting teeth on pollex, some larger and more prominent. Carpi on either side with one prominent tooth and two rudimentary teeth. Meri granulated with spine on anterior surface. Slender pereopods (P2: ML/MW = 3.75; P5: ML/MW = 3.61), pereopod 4 longest, pereopod 5 shortest. Ventral margins of propodi smooth, dorsal margins bearing fine serration, dactyli serrated, ending in sharp points.

Pleon (Fig. 4b ). Somites 1-6 four sided, with triangular distally-rounded terminal segment (telson). First 5 somites broad and short; somite 6 and telson longer.

Pleopods (Fig. 5f-i ). Gonopod 1 terminal segment short, 0.24 length of subterminal segment, widest at base, tapering, ends in sharp point at distal end of terminal segment. Medial margin slightly irregular, inner lateral margin curved, margins hirsute. Terminal segment curves away from medial line when viewed posteriorly. Longitudinal groove extending the length of both subterminal and terminal segment, visible on dorsal surface. Gonopod 2 consisting of two segments; terminal segment 0.57 times length of subterminal segment, filamentous; subterminal segment widest at base, tapering gently inward 0.4 of length, forming narrow process supporting terminal segment. Gonopod 2 with straight subterminal segment, terminal segment curves inward toward medial line.

Variation.

The major cheliped is not always distinctly arched, especially in females and juveniles.

Live colouration.

Colouration varies between orange-brown to a darker purple-brown when alive. Tips of the dactyli may be paler in colour, displaying as orange or paler brown/purple.

Distribution.

Currently known only from the Katberg State Forest, the Hogsback State Forest, Madonna and Child Falls and the Hogsback Arboretum, all situated in the Amathole Mountain Range in the Eastern Cape province of South Africa.

Etymology.

The species is named after the Amathole Mountains, part of the Winterberg-Amathole mountain range complex, located on the Great Escarpment in the Eastern Cape. It is currently thought to be endemic to this region. The isiXhosa name ‘Amathole’ translates to ‘calves’ in English and refers to the mountain range, the forest, and the municipal district.

Remarks.

Potamonautes amathole sp. nov. is genetically and morphologically most similar to the Western Cape small-bodied montane freshwater crabs, i.e., P. brincki (Bott, 1960), P. parvispina Stewart, 1997, P. parvicorpus Daniels, Stewart & Burmeister, 2001, and P. tuerkayi Wood & Daniels, 2016. Morphologically, the species can be most easily distinguished from P. parvispina by the latter’s small but pronounced epibranchial tooth. Potamonautes parvicorpus bears slightly arched chelipeds, an arched carapace, and a poorly developed postfrontal crest, while the new species has highly arched major chelipeds, a flattened carapace and a distinct postfrontal crest. Potamonautes brincki also has an arched carapace as well as a partitioned terminal segment of the mandibular palp with a setae-covered flange. Potamonautes amathole sp. nov. has a unilobed terminal segment of the mandibular palp with no flange. Of all the Western Cape montane freshwater crabs, P. tuerkayi is the most similar to P. amathole sp. nov. However, P. tuerkayi has a sharply tapering subterminal segment of gonopod 2, forming a rounded subterminal base, while in P. amathole sp. nov. this tapering is gradual, forming a sloping instead of a rounded base. Geographically, the above-mentioned species are all confined to the Cape Fold Mountain region, with P. amathole sp. nov. being the first described small-bodied montane freshwater crab from the Eastern Cape part of the Great Escarpment.

Potamonautes depressus and P. clarus are two species of highland river crabs in the Drakensberg Mountain range. Although superficially similar to P. amathole sp. nov. in terms of a flattened carapace and slender limbs, morphological differences do exist in the structure of the mandibular palp and carapace depression. In P. clarus , a bright orange species, the mandibular palp has a flange on the terminal segment, while this is absent in P. amathole . Potamonautes depressus has an extremely flattened carapace, with CH/CL ranging from 0.38-0.43. In P. amathole sp. nov., this depression of the carapace is less extreme with a ratio ranging from 0.43-0.51. Both of these species are confined to fast-flowing rivers in the Drakensberg highlands. In most other Potamonautes spp., pereopod 3 is the longest. However, in P. amathole sp. nov., pereopod 4 appears to be the longest.

Habitat and ecology.

Hogsback and Katberg are both situated in the Keiskamma River catchment. Both sites consist of Southern Mistbelt Forest (FoZ 3), known to be tall, multi-layered, species-rich forests dominated by Afrocarpus falcatus , Celtis africana , Calodendrum capense , Vepris lanceolata , and Zanthoxylum davyi ( Mucina and Rutherford 2006). Within the forest and grassland, patches of Eastern Temperate Freshwater Wetlands (AZf3) can be found ( Mucina and Rutherford 2006).

The Hogsback (Madonna and Child) Waterfall site is situated inside the Hogsback State Forest. The habitat is represented by a tall, high-flowing stream with different biotopes and pools rich in macro-invertebrate diversity, i.e., Ephemeroptera , Coleoptera , Hemiptera , Diptera , Trichoptera , Odonata , and Plecoptera ( Griffiths et al. 2015). The substrate is largely bedrock with sand and large stones. The site is characterised by a diversity of flora species, including Canthium ciliatum , Protorhus longifolia , Afrocarpus falcatus , and Scolopia mundii (Hawley et al. 2004; Mucina and Rutherford 2006).

The second site is situated inside the Hogsback Arboretum Park, downstream from the 39 Steps Waterfall. The habitat is represented by a small stream with pools and the substrate is largely sand with rocks. The edge of the stream is represented by marginal vegetation (i.e., Pseudoschoenus inanis ) with tree canopy cover and burrows ( Griffiths et al. 2015). The site is characterised by a diversity of planted flora species.

The Katberg site is situated in the montane Katberg State Forest. This habitat is comprised of a trickling stream on a very steep slope. The habitat is represented by low and clean water with some other macro-invertebrate diversity, i.e., Ephemeroptera , Coleoptera , Hemiptera , Diptera , Trichoptera , and Odonata ( Griffiths et al. 2015). The substrate is largely bedrock with sand and stones. The edge of the stream is represented by marginal vegetation with dense tree canopy cover and burrows. The site is characterised by a diversity of flora species, including C. ciliatum , and P. longifolia (Hawley et al. 2004; Mucina and Rutherford 2006).

At the Hogsback Arboretum site, P. amathole sp. nov. co-occurs with P. danielsi . Potamonautes danielsi is also found at the nearby Municipal Dam.

Figures

Figure 4. Potamonautes amathole sp. nov. male holotype (MB-A 094813) a dorsal view b ventral view, and c cephalothorax, frontal aspect. Scale bar: 10 mm.

Figure 5. Potamonautes amathole sp. nov. male holotype (MB-A 094813) 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 g left gonopod 1 posterior view h left gonopod 2 posterior view, and i left gonopod 2 anterior view. Scale bars: 10 mm (a, b); 1 mm (c, d); 5 mm (e-i).