taxonID	type	description	language	source
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	description	(Figures 1 – 5, 10)	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	materials_examined	Type material. Holotype: MCZ CRU- 7678, adult female (CW 52.0 mm, CL 35.0 mm), Tanzania, Uluguru Mountains, Bagilo (- 7.105079, 37.654157, 1,935 m ASL), coll. A. Loveridge, September 1926. Paratypes: MCZ CRU- 7678 a, adult male (CW 33.0 mm, CL 21.0 mm), same data as holotype. – MCZ CRU- 7678 b, 3 adult males (no measurements available), 2 adult females (no measurements available), same data as holotype. Other material examined: NMU TRWEA 62.45, subadult male (CW 31.6 mm), subadult female (CW 41.1 mm), 2 juvs. (CWs 17.1, 16.3 mm), Tanzania, Uluguru Mountains, Bunduki, Kitange-Tange River, tributary of Mgeta River 2.4 – 3.0 m wide, near Hululu Waterfalls Mgeta (- 7.049021, 37.642489, 1,603 m ASL), riverbed with large boulders, gravel, stones and sand, coll. T. R. Williams, 23 February 1962. – NMU TRWEA 62.47, 2 subadult males (CWs 29.8, 27.0 mm), 4 juvs. (CWs 15.6 mm, 15.9 mm, 16.2 mm, 17.8 mm), Tanzania, Uluguru Mountains, Bunduki rest house, Kitange-Tange River, 1859 – 1890 m ASL, river falling rapidly over large boulders, with gravel flats and occasional large stones, coll. T. R. Williams, 23 February 1962. – NMU TRWEA 62.49 (illustrated), adult male (CW 33.6 mm, CL 23.4 mm, CH 11.1 mm, FW 10.6 mm), adult female ovigerous (CW 28.3 mm), Tanzania, Bunduki, Uluguru Mountains, from small, shaded stream near forest margin, coll. T. R. Williams, 23 February 1962.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	diagnosis	Diagnosis. Postfrontal crest sharp-edged, completely crossing carapace; exorbital tooth low but distinct, epibranchial tooth reduced to small granule; (Fig. 1 A, B); anterolateral, lateral carapace margins distinctly granulated; carapace branchiostegite smooth; third maxilliped ischium lacking vertical sulcus; S 3 / 4 incomplete, deep at sides, obscure in middle; thoracic episternal sulci S 4 / E 4, S 5 / E 5 deep, complete, S 6 / E 6, S 7 / E 7 obscure (Fig. 2 B, C). Male right (major) chela dactylus straight, not arched, broad, cutting edge lined by large teeth, largest proximally, becoming smaller distally; cheliped merus stout, anterior inferior margin lined by small teeth, distal meral tooth large, posterior inferior margin smooth (Fig. 3 C, D); cheliped carpus inner margin distal tooth medium sized pointed, proximal tooth small, pointed, followed by two granules (Fig. 3 E); G 1 TA about 1 / 3 G 1 SA length (G 1 TA / G 1 SA 0.4), basal half straight, distal half curved outward at 45 ° to longitudinal axis of G 1 SA; G 1 TA tapering to pointed straight tip, mid-section widened by additional rounded crest on dorsal lobe with distinct setae on ventral lobe; G 1 TA dorsal, ventral lobes separated in middle by long groove (Figs. 4 A – C, 5 B, C).	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	description	Description. Carapace surface smooth, widest in anterior third (CW / FW 3.1), medium height (CH / FW 1.1) (Figs. 1 A, B, 2 A), semi-circular, urogastric grooves deep; cardiac region weakly marked, cervical grooves short, faint; transverse branchial grooves faint (Fig. 1 A, B). Front about 1 / 3 carapace width (FW / CW 0.3); frontal margin straight (Figs. 1 A, B, 2 A); exorbital tooth small, blunt; epibranchial tooth reduced to granule; postfrontal crest sharply defined, complete, traversing entire carapace; lateral carapace margin posterior to epibranchial tooth granulated (Fig. 1 A, B). Branchiostegite with two sutures, one longitudinal (epimeral), one vertical, dividing carapace sidewall into suborbital, subhepatic, pterygostomial regions, all smooth (Fig. 3 A). Third maxillipeds filling entire oral field, except for transversely oval efferent respiratory openings at superior lateral corners, exopod with long flagellum, endopod ischium smooth (Fig. 2 D). Mandibular palp consisting of basis plus two articles; terminal article simple, undivided, lacking lobe or ridge at junction between articles (Fig. 2 E). Anterior, posterior male thoracic sternum surface completely smooth; sternal sulci S 1 / 2, S 2 / 3 completely traversing sternum; S 3 / 4 incomplete, deep at sides, obscure in middle; thoracic episternal sulci S 4 / E 4, S 5 / E 5 deep, complete, S 6 / E 6, S 7 / E 7 obscure (Fig. 2 B, C). Male right (major) chela dactylus straight, not arched, broad, cutting edge lined by large teeth, largest proximally, becoming smaller distally; immovable finger (propodus pollex) broad, cutting edge lined by large teeth, largest proximally, becoming smaller distally; tips of both fingers touching when chela closed, enclosing long narrow interspace; major chela propodus palm enlarged, swollen, lower margin curving downward, distinctly convex, cutting edge toothed, largest teeth proximally, becoming smaller distally (Fig. 3 A). Male left (minor) chela dactylus slim, gently curved, cutting edge with large teeth proximally, small teeth distally; propodus pollex cutting edge lined by large teeth, largest proximally, becoming smaller distally; tips of both fingers touching when chela closed, enclosing long narrow interspace; minor chela propodus palm subequal to that of major chela; lower margin gently curved, convex (Fig. 3 B). Cheliped merus stout, anterior inferior margin lined by small teeth, distal meral tooth large, posterior inferior margin smooth (Fig. 3 C, D); cheliped carpus inner margin distal tooth medium sized, pointed; proximal tooth small, pointed, followed by two granules (Fig. 3 E); ambulatory legs P 2 – 5 stout, distal limb articles (merus, carpus, propodus, dactylus) not elongated; dactyli of P 2 – 5 tapering to point, each bearing four rows of downward-pointing sharp bristles (Fig. 1 A). Male pleon, telson together forming slim triangle; pleon edges slightly indented; telson triangular, apex rounded, base broadest, sides outwardly sloping; pleomeres PL 1 – 6 rectangular, wider than long, PL 6 longest, more than 1 / 2 as long as wide; remaining pleomeres short, less than 1 / 3 as long as wide (Fig. 2 B, C). G 1 TA about 1 / 3 G 1 SA length (G 1 TA / G 1 SA 0.4), basal half straight, distal half curved outward at 45 ° to longitudinal axis of G 1 SA; G 1 TA with setae on lateral margin, rounded crest in midsection, distal third tapering to pointed straight tip; G 1 TA dorsal lobe low, ventral lobe low widened by additional rounded crest in mid-section which has long setae; lobes separated in middle by thin groove (Fig. 4 A – C, 5 B, C). G 1 SA widest at base, narrowest at G 1 TA-G 1 SA junction; G 1 SA mesial, lateral margins lined by long setae (Fig. 4 A, 5 B). G 2 SA (Fig. 5 A) long, slim, subequal to G 1 SA; G 2 SA widest at base, tapering sharply inward about one-third along length, last 2 / 3 rds forming long, thin, tapering, upright process supporting long flagellum-like G 2 TA (G 2 TA / G 2 SA 0.5) (Fig. 5 A). Size. Medium-sized species, the adult size range is between CW 33.0 – 52.0 mm.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	materials_examined	Type locality. Tanzania, Uluguru Mountains, Bagilo.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	description	Colour. Living male specimens have a purple-pink carapace and paler walking legs. Carapace of living female distinctly mottled with darker areas. Specimens preserved in ethanol are light brown.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	biology_ecology	Habitat. At Bunduki in the Uluguru Mountains this species is most abundant either near, or within, higher altitude forest and occurs only rarely at lower altitudes. Crabs were collected from a small shaded stream near the forest margin.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	distribution	Distribution. Endemic to the Uluguru Mountains, Tanzania, East Africa (Fig. 10).	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	conservation	Conservation status. Arcopotamonautes unisulcatus is currently assessed as vulnerable because it is only known from two locations, has a restricted extent of occurrence, less than 20,000 km ²), and a small area of occupancy that are both below the thresholds for vulnerable (IUCN 2004). In addition, its distribution is fragmented, and it is threatened by a continuing decline in the extent and quality of its habitat due to degradation driven by human population increases and industrial and agrarian development, and A. unisulcatus is not found in a protected area.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF15FFF5F7C7FB4B17817F1D.taxon	discussion	Remarks. Bott (1955) treated Potamon (Potamonautes) unisulcatus Rathbun, 1933 as a junior synonym of A. johnstoni (Miers, 1885). The present study, however, agrees with the opinion of Reed & Cumberlidge (2006) that both of these taxa are each valid species. Arcopotamonautes unisulcatus is redescribed here because the earlier redescription of this species by Reed & Cumberlidge (2006) provided only a brief account and did not make comparisons with other species. In addition, the earlier descriptions have been expanded by adding new taxonomic characters such as mandibles and gonopods that were not previously described. Furthermore, this species is also compared with similar newly-described taxa from the region. Comparisons. Arcopotamonautes (Bott, 1955) currently comprises 18 species from the D. R. Congo, Kenya, Malawi, Rwanda, Tanzania, and Zambia (Reed & Cumberlidge 2006; Cumberlidge & Daniels 2022; Cumberlidge & Jonas 2024; Cumberlidge & Conners 2025). Arcopotamonautes unisulcatus can be distinguished from A. suprasulcatus (Hilgendorf, 1898), A. xiphoidus (Reed & Cumberlidge, 2006), A. infravallatus (Hilgendorf, 1898), and A. bellarussus (Daniels, Phiri & Bayliss, 2014) by the form of the G 1 TA, which is distinctly widened in the midsection in A. unisulcatus (Figs. 4 A – C, 5 A, C, 9 A – C, 10 B, C) (versus slim, curved, and needle-like in A. suprasulcatus and A. bellarussus (Daniels et al. 2014: fig, 5 A, B), or cone-shaped, not widened, and tapering to a pointed tip in both A. xiphoidus (Fig. 9 A, B) and A. infravallatus; Cumberlidge & Conners 2025: figs. 1 A, B, D, 6 E). Arcopotamonautes unisulcatus can be distinguished from A. orbitospinus (Cunnington, 1907) from Lake Malawi and A. platynotus (Cunnington, 1907) from Lake Tanganyika by the form of the carapace lateral margin which is granular in A. unisulcatus (Figs. 1 A, B, 6 A, B) (versus a lateral margin that has several teeth behind the epibranchial tooth in A. orbitospinus (Reed & Cumberlidge 2006: pl. V, A, B; fig. 42 as Potamonautes lirrangensis), and A. platynotus; Reed & Cumberlidge 2006: fig. 94). Arcopotamonautes unisulcatus can be distinguished from A. platycentron (Hilgendorf, 1897) from Lake Chala (Kenya and Tanzania) by the form of the cheliped carpus distal tooth, which is slim and pointed in A. unisulcatus (Figs. 3 C, 8 E) (versus extremely broad, flat and blunt in A. platycentron; Reed & Cumberlidge 2006: figs. pl. IX, A). Arcopotamonautes unisulcatus can be distinguished from A. amosae (Cumberlidge, Johnson, Clark & Genner, 2021), A. caputanatis Cumberlidge, Clark & Fastiggi, 2019), A. johnstoni (Miers, 1885), A. raybouldi (Cumberlidge & Vannini, 2004), A. gerdalensis (Bott, 1955) and A. montivagus (Chace, 1953) by the form of the G 1 TA, which has a rounded low crest arising out of the dorsal lobe in A. unisulcatus (Figs. 4 A – C, 5 A, C, 9 A – C, 10 B, C) (versus a G 1 TA, where a high thin crest arises from the dorsal lobe in A. amosae, A. caputanatis, A. johnstoni (Reed & Cumberlidge 2006: figs. 151, 152), A. raybouldi (Reed & Cumberlidge 2006: figs. 165, 166), A. gerdalensis (Reed & Cumberlidge 2006: figs. 147, 148), and A. montivagus; Chace 1953: fig. 3 e – g, j). Arcopotamonautes unisulcatus can be distinguished from A. parekeeae Cumberlidge & Jonas, 1924 and A. ngae Cumberlidge & Jonas, 1924 by the sulci on the anterior thoracic sternum, where the S 3 / 4 is missing except for two short notches at the margins in A. unisulcatus (versus deep and completely traversing the thoracic sternum in A. parekeeae and A. ngae (Cumberlidge & Jonas, 1924: figs. 2 B, C, 7 B, C )). Finally, A. unisulcatus can be distinguished from A. picus Cumberlidge & Conners, 2025 by the form of the G 1 TA, which is distinctly widened in the midsection in A. unisulcatus (Figs. 4 A – C, 5 A, C, 9 A – C, 10 B, C) (versus slim and tapering to a slightly upcurved tip in A. picus; Cumberlidge & Conners 2025: fig. 4 A, B, D – F).	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF1CFFF0F7C7FD6F131F7DF5.taxon	description	(Figures 6 – 10)	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF1CFFF0F7C7FD6F131F7DF5.taxon	materials_examined	Type material. Holotype: NMU TRW 1966.06 b, adult male (CW 38.3 mm, CL 26.1 mm, CH 15.6 mm, FW 11.4 mm), Tanzania, West Usambara Mountains, Herkulu Estate, Lushoto District, Tanga region, coll. J. N. Raybould, November 1964. Paratype: NMU TRW 1966.06 b, adult male (CW 27.2 mm, CL 19.3 mm, CH 11.7 mm, FW 8.4 mm), same data as holotype. Other material examined. NMU TRW 1966.06 a, 5 subadult & adult males (CWs 16.1 – 33 mm), 2 adult females (CWs 30.9 mm, 33.1 mm), 6 subadult & adult females (CWs 16.0 – 25.3 mm) Tanzania, West Usambara Mountains, streams and dams near Herkulu Estate, Lushoto District, Tanga region, coll. J. N. Raybould, November 1964. – USNM 64108, female (damaged), male (damaged), Tanzania, East Usambara Mountains, Amani, coll. A. Loveridge, 8 December 1926.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF1CFFF0F7C7FD6F131F7DF5.taxon	diagnosis	Diagnosis. Exorbital tooth small, blunt; epibranchial tooth reduced to granule; postfrontal crest sharply defined, complete, traversing entire carapace; carapace lateral margin posterior to epibranchial tooth smooth (Fig. 6 A, B). Branchiostegite suborbital, subhepatic, pterygostomial regions, all smooth (Fig. 7 A, B). Ischium of third maxilliped with deep vertical sulcus (Fig. 8 E). Dactylus of except for several small granule-like teeth distally; both finger tips touching when chela closed, enclosing long oval interspace; major chela propodus palm enlarged, swollen, lower margin distinctly concave (Fig. 8 A). G 1 TA smooth, tapering sharply to pointed straight tip; G 1 TA widened basally; ventral, dorsal lobes low (Fig. 7 A, B).	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF1CFFF0F7C7FD6F131F7DF5.taxon	description	Redescription. Carapace surface smooth, widest in anterior third (CW / FW 3.4), medium height (CH / FW 1.4) (Figs. 6 A, B, 7 A), semi-circular groove deep, urogastric, cardiac, cervical, transverse branchial grooves faint (Fig. 6 B). Front about 1 / 3 carapace width (FW / CW 0.3); frontal margin slightly indented (Figs. 6 B, 7 A); exorbital tooth small, blunt; epibranchial tooth reduced to granule; postfrontal crest sharply defined, complete, traversing entire carapace; carapace lateral margin posterior to epibranchial tooth smooth (Figs. 6 A, B, 7 A). Branchiostegite with two sutures, one longitudinal (epimeral), one vertical, dividing carapace sidewall into suborbital, subhepatic, pterygostomial regions, all smooth (Fig. 7 A). Third maxillipeds filling entire oral field, except for transversely oval efferent respiratory openings at superior lateral corners (Fig. 7 A), exopod with long flagellum maxilliped, endopod ischium with deep vertical sulcus (Fig. 8 E). Mandibular palp consisting of basis plus two articles; terminal article undivided, lacking ridge at junction between articles (Fig. 7 D – F). Thoracic sternum S 4 outer margin thickened and raised, sternal sulci S 1 / 2, S 2 / 3 completely traversing sternum; S 3 / 4 deep, V-shaped, completely traversing sternum; thoracic episternal sulci S 4 / E 4, S 5 / E 5, S 6 / E 6, S 7 / E 7 present (Fig. 7 A, B). Dactylus of male right (major) chela distinctly arched, slim, cutting edge lacking teeth except for several small granule-like teeth distally; immovable finger (propodus pollex) slim, cutting edge with two medium teeth proximally; both finger tips touching when chela closed, enclosing long oval interspace; palm of propodus of major chela enlarged, swollen, lower margin distinctly concave (Fig. 7 A). Dactylus of male left (minor) chela long, slim, gently curved, cutting edge lined by series of small teeth; immovable finger (propodus pollex) with four medium teeth interspersed by small teeth; both fingers touching at tip when chela closed, enclosing long oval interspace; palm of propodus of minor chela subequal to that of major chela, 0.8 × propodus height of major chela; lower margin slightly concave (Fig. 7 B). Cheliped merus elongated, almost as long as CW; inferior margin proximally with three granule-like teeth and larger one at midpoint, otherwise smooth, distal meral tooth lacking (Fig. 8 C, D); cheliped carpus inner margin distal tooth medium sized, blunt; proximal tooth small, blunt, margin behind it granulated (Fig. 8 C); ambulatory legs P 2 – 5 long, distal limb articles (merus, carpus, propodus, dactylus) elongated; dactyli of P 2 – 5 tapering to point, each bearing four rows of downward-pointing sharp bristles (Fig. 6 A). Male pleon together with telson forming slim triangle; telson triangular, apex rounded, base broadest, sides slightly indented inwardly sloping; pleomeres PL 1 – 6 rectangular, wider than long, PL 6 longest, more than 1 / 2 as long as wide; remaining pleomeres short, less than 1 / 3 as long as wide (Fig. 7 B, C). G 1 TA about 1 / 3 G 1 SA length (G 1 TA / G 1 SA 0.3), angled outward at 45 ° to longitudinal axis of G 1 SA; G 1 TA smooth, lined by short setae, tapering sharply to pointed straight tip; G 1 TA widened basally; ventral, dorsal lobes low (Fig. 9 A, B). G 1 SA widest at base, narrowest at G 1 TA-G 1 SA junction; basal G 1 SA mesial margin lined by sparse short setae; G 1 SA lateral margin mostly smooth (Fig. 9 A, B). G 2 SA (Fig. 9 C) long, slim, subequal to G 1 SA; G 2 SA widest at base, tapering sharply inward about one-third along length, last 2 / 3 rds forming long, thin, tapering, upright process supporting long flagellum-like G 2 TA (G 2 TA / G 2 SA 0.6) (Fig. 9 C). Size. Medium-sized species, adult size range between CWs 24 – 38 mm.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF1CFFF0F7C7FD6F131F7DF5.taxon	materials_examined	Type locality. The Herkulu Estate is a tea plantation in the Western Usambara Mountains in Lushoto District of the Tanga region of Tanzania (Fig. 10). This locality is situated in the montane forest zone (1,666 m ASL) where much of the forest has been cleared, but patches of forest have been retained to prevent soil erosion.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF1CFFF0F7C7FD6F131F7DF5.taxon	distribution	Distribution. This species is endemic to the East and West Usambara Mountains in Tanzania (Fig. 10). The rivers of the western slopes of the Usambaras drain into the Pangani River, while the eastern slopes of these mountains are drained by the Sigi River and its tributaries.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF1CFFF0F7C7FD6F131F7DF5.taxon	conservation	Conservation status. Arcopotamonautes xiphoidus is assessed as vulnerable because it is still known only from three localities, has a narrow extent of occurrence, and a restricted area of occupancy that are all below the thresholds for vulnerable (IUCN 2004). This species is threatened by increasing habitat disturbance and destruction by deforestation associated with growing human populations in the region. In addition, A. xiphoidus is not found in a protected area.	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
532B87DDFF1CFFF0F7C7FD6F131F7DF5.taxon	discussion	Remarks. Arcopotamonautes xiphoidus is morphologically close to A. unisulcatus, but the two taxa can be recognized by differences in the G 1 TA, which is long, straight, smooth, evenly-tapering, and spear-like in A. xiphoidus (Fig. 9 A, B) (versus curved and tapering to a pointed straight tip, with a mid-section widened by an additional rounded crest, and distinct setae on the ventral lobe in A. unisulcatus; Figs. 4 A, B, 5 A – C).	en	Cumberlidge, Neil, Huiskens, Alyssa J., Jonas, Gabrielle I. (2025): Redescription of two species of freshwater crabs from Tanzania, East Africa: Arcopotamonautes unisulcatus (Rathbun, 1933) and A. xiphoidus (Reed & Cumberlidge, 2006) (Brachyura: Potamoidea: Potamonautidae). Zootaxa 5659 (4): 565-580, DOI: 10.11646/zootaxa.5659.4.6, URL: https://doi.org/10.11646/zootaxa.5659.4.6
