Potamonautes macrobrachii Bott, 1953

Cumberlidge, Neil, Ahles, Katelyn M. & Daniels, Savel R., 2021, Redescriptions of three species of freshwater crabs from Angola, southern Africa (Brachyura: Potamoidea: Potamonautidae), Zootaxa 5032 (4), pp. 516-532 : 521-530

Potamonautes macrobrachii Bott, 1953

( Figs. 3 , 4C , 5E, F, K, L , 6C, F , 7C , 8 )

Potamonautes (Isopotamonautes) macrobrachii Bott, 1953: 138–139 , pl. 4, 5; Bott 1955: table IX, fig. 2 a–d, pl. 25, 78.b Potamonautes macrobrachii, Cumberlidge & Tavares, 2006: 248 , 250, 253–256, table 1; Cumberlidge 2008b: 1–8, fig. 1; Ng

et al. 2008: 171.

Holotype. SMF 1892 , adult male (CW 32.91, CL 22.3, CH 10.9, FW 10.9 mm), Angola, Benguala, Huambo Province, Luimbale, Serra do Moco (escarpment of Moco ) (-12.466667, 15.166667) 1,800 m ASL, Kuketa stream (tributary of the Catumbela River ) draining the Mount Moco Special Reserve , 5 Sep. 1949, coll. A. de Barros Machado.

Rediagnosis. Surface of carapace completely smooth with no deep grooves, granules, or carinae; postfrontal crest completely crossing carapace, low in middle, sharp laterally, extending to meet anterolateral margins ( Figs. 3A , 4C ). Exorbital tooth small, low, blunt; epibranchial tooth reduced to granule; anterolateral margin posterior to epibranchial tooth smooth, posterior end continuous with posterolateral margin ( Fig. 3A, B ). S3/4 complete, deep, v-shaped, meeting anterior margin of sternopleonal cavity; outer margins of S4 thickened, raised ( Figs. 3B , 4C ). Third maxilliped ischium vertical sulcus either lacking, or very faint ( Fig. 3B ). Distal, proximal teeth on cheliped carpus inner margin both reduced to granules ( Figs. 3A , 5L ). G1 TA short ( TA / SA 0.33), basal half angled slightly outward at 50 ° to longitudinal axis of G1 SA, distal third tapering to pointed tip; G1 TA widened in midsection by distinctly raised rounded mesial, lateral folds, equally high, ( Fig. 6C, F ); longitudinal groove of G1 TA visible along proximal two-thirds. G2 TA long, flagellum-like (G2 TA / SA 0.33) ( Fig. 7C ).

Redescription. Male holotype. Carapace with moderate width (CW/FW 3.0), length (CL/ FW 2.0), height ( CH /FW 1.0); surface completely smooth with no deep grooves, granules, or carinae; semicircular, urogastric, cardiac, branchial grooves all faint; epigastric crests low, separated by clear, short, forked mid-groove; postfrontal crest completely crossing carapace, low in middle, sharp laterally, meeting anterolateral margins ( Fig. 3A ). Exorbital tooth small, low, blunt, epibranchial tooth reduced to granule; anterolateral margin between exorbital, epibranchial teeth smooth, straight, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth smooth, posterior end continuous with posterolateral margin ( Fig. 3A ). Branchiostegite with faintly granulated vertical sulcus; subhepatic, suborbital, pterygostomial regions all smooth ( Figs. 3B , 4C ). Third maxillipeds filling entire oral field, except for transversely oval efferent respiratory openings; exopod with long flagellum, ischium vertical sulcus faint ( Fig. 3B ). Mandibular palp 2-articled; terminal article lacking anterior lobe or ledge. Thoracic sternal sulcii S1/2, S2/3 deep, completely traversing sternum; S3/4 complete, deep, v-shaped, meeting anterior margin of sternopleonal cavity; outer margins of S4 thickened, raised; thoracic episternal sulci S4/E4, S5/E5, S6/ E6, S7/E7 each obscure.

Chelipeds unequal, right (major) longer, higher than left (minor) ( Fig. 3A ). Dactylus of right chela slim, distinctly arched, enclosing broad oval interspace when closed; propodus palm swollen. Movable finger (dactylus) lacking teeth proximally, distal half with 5 small well-spaced small teeth; fixed finger (pollex of propodus) of right chela with 4 widely spaced small teeth ( Fig. 5E, F ). Cheliped carpus inner margin distal, proximal teeth both heavily reduced, proximal tooth granule-sized ( Fig. 5L ). Cheliped merus lower margins both lined by granules, distal meral tooth low, blunt ( Fig. 5K ). Ambulatory legs (P2–5) slender, P5 shortest; dactyli P2–5 tapering to point, each bearing rows of downward-pointing sharp bristles ( Fig. 3A ).

Male pleon, telson together forming slim triangle, pleon edges slightly indented; telson triangular, apex round- ed, base broadest, sides outwardly sloping; pleomeres PL1–6 rectangular, wider than long, PL 6 longest, more than 1/2 as long as wide ( Fig. 3B ); remaining pleomeres short, less than 1/3 as long as wide. G1 TA short, about 1/3 as long as SA (G1 TA/SA 0.33), angled outward at midpoint at 50° to longitudinal axis of G1 SA; G1 TA midsection distinctly widened by raised rounded mesial fold, lateral fold low throughout length ( Fig. 6C, F ); distal third of G1 TA slim, tapering to pointed up-curved tip; proximal two-thirds of G1 TA with longitudinal groove between mesial, lateral folds. G1 SA widest at base, narrowest at G1 TA/SA junction; G1 SA mesial, lateral margins lined by conspicuous long setae; G1 SA ventral side with broad setae-lined fold that partly covers SA basally, completely covers SA at TA/SA junction. G2 TA long, flagellum-like (G2 TA/SA 0.33); G2 SA widest at base, last two-thirds tapering sharply inward forming long, thin, tapering, upright process supporting long G2 TA ( Fig. 7C ).

Size. Medium species, adult at CW 32.0 mm.

Colour. The colour of living specimens is unknown, but specimens preserved in ethanol are light brown.

Type locality. Angola, Benguala, Huambo Province, Serra do Moco (escarpment of Moco) (-12.466667, 15.166667) 2,200 m ASL, Kuketa stream, a tributary of the Catumbela River draining the Mount Moco Special Reserve (1898 m ASL). This high-altitude locality is close to Morro de Moco (2,620 m ASL) which the highest point in Angola ( Fig. 8 ).

Distribution. Potamonautes macrobrachii is known only from just one locality on the escarpment of Serra do Moco (-12.466667, 15.166667) 2,200 m ASL, in Benguala Huambo Province. The specimen was collected from the Kuketa stream, a tributary of the Catumbela River that drains the Mount Moco Special Reserve ( Fig. 8 ).

Habitat. Mount Moco is located in the mountainous province of Huambo, in central-west Angola, and is that country’s highest peak at 2,620 m. The slopes of Mount Moco include steep valleys that support Afromontane forest, while at lower altitudes there is miombo woodland .

Conservation status. Potamonautes macrobrachii was listed in the IUCN Red List of Threatened Species as Data Deficient ( Cumberlidge 2008c) because there is very little information available on its distributional range, population size and trends, or habitat. Although Mount Moco Special Reserve is a protected area it currently receives little protection from unsustainable and unregulated wood collection for logging and firewood, and uncontrolled bush fires. All of this represents a potential threat to the habitat of this little-known species.

Remarks. The affinities of P. macrobrachii (based on similarities of characters of the carapace, chelipeds, and gonopods) place it close to southern African species such as P. mulanjeensis Daniels & Bayliss, 2012 from Mount Mulanje in Malawi and P. mutareensis Phiri & Daniels, 2013 from the eastern Highlands of Zimbabwe ( Daniels & Bayliss 2012; Phiri & Daniels 2013). In Angola, P. macrobrachii is found at the same location as P. anchietae and both share a similar carapace height and frontal margin width ( CH /FW 1.08, P. macrobrachii , 1.07, P. anchietae ; and FW/CW 0.34, P. macrobrachii , 0.32, P. anchietae ), and both have a prominent and complete postfrontal crest, a greatly reduced epibranchial tooth (either granular or missing), a v-shaped thoracic sternal sulcus S3/4 that is deep at the sides and shallow in the middle, and a cheliped merus whose inferior margins are either granular or smooth.

Characters that distinguish P. macrobrachii from P. anchietae include the following: the cheliped merus of P. macrobrachii is greatly elongated ( Figs. 3A , 5K, L ) (vs a cheliped merus of normal length in P. anchietae (cf. Bott 1955: fig. 1a, d); the distal and proximal teeth on the inner margin of the cheliped carpus of P. macrobrachii are both rounded and low ( Figs. 5K, L ) (vs two pointed teeth in P. anchietae (cf. Bott 1955: fig. 1a)); the branchiostegite of P. macrobrachii is divided by two sutures into three parts ( Figs. 3B , 4C ) (vs divided into four parts in P. anchetiae (cf. Cumberlidge & Tavares 2006)); and the G1 TA of P. macrobrachii is strikingly widened in the midsection by a raised, rounded mesial fold that is significantly higher than the lateral fold ( Fig. 6C, F ) (vs a G1 TA that is only slightly widened in the midsection by a low mesial fold that is only slightly higher than the lateral fold in P. anchietae (cf. Bott 1955: fig. 25)).

Figures

FIGURE 3. Potamonautes macrobrachii Bott, 1953, holotype, adult ♂ CW 32.9 mm, from Huamba Province, Angola (SMF 1892). Whole animal, dorsal view (A), whole animal, ventral view (B). Scale bars: A = 12.5 mm, B = 5.38 mm.

FIGURE 4. Frontal view of carapace. (A) Potamonautes adeleae Bott, 1968, paratype, adult ♂ CW 55.3 mm, from Lunda Norte Province, Angola (SMF 4444); (B) Potamonautes kensleyi Cumberlidge & Tavares, 2006, adult male CW 35.4 mm, from the Cuanza River, Soxujwa, Kekere, Malanje Province, Angola (AMG GEN 1887A); (C) Potamonautes macrobrachii Bott, 1953, paratype, adult ♂ CW 32.9 mm, from Huamba Province, Angola (SMF 1892). Photograph B by Theo Busschau, University of Stellenbosch, South Africa. Scale bar: A = 10.4 mm; B = 5.7 mm; C = 4.7 mm.

FIGURE 5. (A–F) Frontal view of right and left chela; (G–L) cheliped merus and carpus. (A, B) Potamonautes adeleae Bott, 1968, paratype, adult ♂ CW 55.3 mm, from Lunda Norte Province, Angola (SMF 4444); (C, D) Potamonautes kensleyi Cumberlidge & Tavares, 2006, adult male CW 35.4 mm, from the Cuanza River, Soxujwa, Kekere, Malanje Province, Angola (AMG GEN 1887A); (E, F) Potamonautes macrobrachii Bott, 1953, holotype, adult ♂ CW 32.9 mm, from Huamba Province, Angola (SMF 1892); (G, H) Potamonautes adeleae Bott, 1968, paratype, adult ♂ CW 55.3 mm, from Lunda Norte Province, Angola (SMF 4444); (G) ventral view of right chela merus; (H) dorsal view of right chela carpus and merus; (I, J) Potamonautes kensleyi Cumberlidge & Tavares, 2006, adult male CW 35.4 mm, from the Cuanza River, Soxujwa, Kekere, Malanje Province,Angola (AMG GEN 1887A) (I) ventral view of right chela merus; (J) dorsal view of right chela merus and carpus; (K, L) Potamonautes macrobrachii Bott, 1953, holotype, adult ♂ CW 32.9 mm, from Huamba Province, Angola (SMF 1892): (K) ventral view of right chela merus; (L) dorsal view of right chela merus and carpus;. Photographs C, D, I, J by Theo Busschau, University of Stellenbosch, South Africa. Scale bar: A = 18.4 mm; B = 17.9 mm; C, D = 8.9 mm; E = 8.33 mm; F = 5.81 mm; G = 17.9 mm; H = 7.3 mm; I = 8.9 mm; J = 5.9 mm; K = 5.81 mm; L = 5.6 mm.

FIGURE 6. Right G1, ventral view (A–C) and dorsal view (D, F). (A, D) Potamonautes adeleae Bott, 1968, paratype, adult ♂ CW 55.3 mm, from Lunda Norte Province, Angola (SMF 4444); (B, E) Potamonautes kensleyi Cumberlidge & Tavares, 2006, adult male CW 35.4 mm, from the Cuanza River, Soxujwa, Kekere, Malanje Province, Angola (AMG GEN 1887A); (C, F) Potamonautes macrobrachii Bott, 1953, holotype, adult ♂ CW 32.9 mm, from Huamba Province, Angola (SMF 1892). Photo- graphs B and E by Theo Busschau, University of Stellenbosch, South Africa. Scale bar: A= 6.7 mm; B = 2.3 mm; C = 1.13 mm; D = 2.7 mm; E = 2.3 mm; F = 1.2.

FIGURE 7. Right G2 ventral view (A–C); (A) Potamonautes adeleae Bott, 1968, paratype, adult ♂ CW 55.3 mm, from Lunda Norte Province, Angola (SMF 4444); (B) Potamonautes kensleyi Cumberlidge & Tavares, 2006, adult male CW 35.4 mm, from the Cuanza River, Soxujwa, Kekere, Malanje Province, Angola (AMG GEN 1887A); (C) Potamonautes macrobrachii Bott, 1953, holotype, adult ♂ CW 32.9 mm, from Huamba Province, Angola (SMF 1892). Photograph C by Theo Busschau, University of Stellenbosch, South Africa. Scale bar: A = 5.6 mm; B = 2.3 mm; C = 1.2 mm.

FIGURE 8. Map of the Angola showing the known localities of Potamonautes adeleae (black square, not shown to scale), P. kensleyi (black circles, not shown to scale), and P. macrobrachii (black diamond, not shown to scale). Scale bar = 520 km. See text for exact locality coordinates.