Arcopotamonautes infravallatus Hilgendorf, 1898

Cumberlidge, Neil & Conners, Paige M., 2024, A new species of freshwater crab from the East Usambara Mountains of Tanzania, East Africa, with a redescription of Telphusa infravallata Hilgendorf, 1898 (Brachyura: Potamoidea: Potamonautidae), Zootaxa 5538 (4), pp. 339-356 : 345-355

Arcopotamonautes infravallatus Hilgendorf, 1898

( Figs. 5–11 )

Telphusa infravallata Hilgendorf, 1898: 12–13 , fig 2, 2a.

Potamon (Potamonautes) infravallata — Rathbun 1905: 174.

Potamon (Potamonautes) usambarae Rathbun, 1933: 257 , 258, pl. 6 fig. 1–4.

Potamon infravallatus — Chace 1942: 213.

Potamonautes (Rotundopotamonautes) infravallatus — Bott 1955: 293–294, pl. XXV fig. 2a–d, fig. 57.

Potamonautes infravallatus — Reed & Cumberlidge 2006: 3 , 5, 7, 9–11,14,19, 20, 40, 57–60, 135, 137, 138, 149, 150, 175, pl. III figs. 23–30, tab. 4 [part]. — Ng et al. 2008: 171.

Arcopotamonautes xiphoidus — Reed & Cumberlidge 2006: 14, 38, 39 [part], figs. 134–144, 171–172, 186, pl. XIV, tabs 1, 2, 4.

Arcopotamonautes infravallatus — Cumberlidge & Daniels 2022: 1274, 1294, 1298, 1299.

Type material. Holotype: ZMB 11378 , adult male ( CW 23.4 , CL 15.4, CH 7.4, FW 6.5 mm), Tanzania, Bulwa , East Usambara Mountains (-5.037767, 38.640919, 880 m ASL), coll. Eismann.

Potamon (Potamonautes) usambarae Rathbun, 1933 , MCZ 7680 , adult male co-type ( CW 22.4 , CL 16.8, CH 6.8, FW 6.0 mm), female subadult co-type ( CW 12.2 , CL 9.5, CH 4.9, FW 3.6 mm), Tanzania,Amani, East Usambara Mountains , coll. A. Loveridge, December 1926.

Other material examined. ZMB 8522 , adult male ( CW 22.4 , CL 16.8, CH 6.8, FW 6.0 mm), Tanzania, Amani Area , East Usambara Mountains (-5.099956, 38.633290, 906 m ASL), coll. Conradt. NMU TRW1966.12 a, 3 subadult and adult males (CWs 19.8–22 mm), adult female ( CW 24.1 mm), 2 subadult females (CWs 21.4, 19.8 mm), Tanzania, Amani Area , East Usambara Mountains, coll. J. N. Raybould, May 1966. NMU TRW1967.11 , adult female ( CW 22.8 mm), Tanzania, West Usambara Mountains , Milinga River , Tewe near Mlalo (-4.525656, 38.346324, 956 mm ASL), coll. J. N. Raybould, 18 February 1967. NMU TRW1970.09 , 7 subadult and adult males (CWs 17.6–25.6 mm), 2 adult females (CWs 27.0, 24.2 mm), 3 subadult females (CWs 18.7–20.0 mm), 2 juveniles (CWs 11.6, 10.9 mm), juvenile female ( CW 13.0 mm), Tanzania, Amani Area , East Usambara Mountains, coll. J. N. Raybould, 1970. NMU TRW1975.01 , 1 specimen, Tanzania, West Usambara Mountains , 3 km north of Mazumbai (-4.792501, 38.504478, 1,413 m ASL), coll. Dunbar, 13 February 1975.

Diagnosis. Exorbital tooth small, pointed ( Figs. 5A–C , 7A, B ); margins of thoracic sternite S4, distinctly raised, thickened ( Fig. 8B ); S3/4 U-shaped, distinct at margins faint in middle ( Fig. 8B, C ); medial inferior margin of cheliped merus lined by small teeth, lateral inferior margin lined by granules, distal meral tooth small ( Fig. 9C, D ); cheliped carpus inner margin distal tooth large pointed, proximal tooth extremely small but pointed ( Fig. 9C ); male right (major) chela dactylus robust, straight, not curved, with three small teeth proximally ( Fig. 9A ); G1TA stout, cone-like with short setae along length, tapering to pointed tip ( Fig. 10A–C ).

Description. Carapace surface smooth, widest in anterior third (CW/FW = 3.2), medium height ( CH /FW 1.3) ( Figs. 5A , 7A, B ), semi-circular, urogastric grooves deep; cardiac region weakly marked, cervical grooves short, faint, transverse branchial grooves faint ( Figs. 5A , 7A, B ). Front width about 1/3 carapace width (FW/CW 0.3); frontal margin straight ( Fig. 8 ); exorbital tooth small, pointed; epibranchial tooth reduced to granule; postfrontal crest sharply defined, complete, crossing entire carapace, meeting epibranchial teeth; carapace lateral margin posterior to epibranchial tooth smooth ( Figs. 5A–C , 7A, B ). Branchiostegite with two granulated sutures, one longitudinal (epimeral), one vertical, dividing carapace sidewall into suborbital, subhepatic, pterygostomial regions, each with smooth surface ( Figs. 5B, C , 8B ).

Third maxillipeds filling entire oral field, except for transversely oval efferent respiratory openings at superior lateral corners; third maxilliped exopod with long flagellum, ischium with deep vertical sulcus ( Figs. 8B , 9E ). Mandibular palp consisting of basis plus two articles; terminal article undivided, with small hardened ridge at junction between articles ( Fig. 9F, G ). Margins of thoracic sternite S4, distinctly raised, thickened; sternal sulci S1/2, S2/3 completely traversing sternum; S3/4 U-shaped, distinct at margins faint in middle; thoracic episternal sulci S4/E4 distinct, S5/E5, S6/E6, S7/E7 all obscure ( Fig. 8B, C ).

Male right (major) chela dactylus (movable finger) short, robust, straight, not curved, with three well-spaced medium teeth interspersed by small teeth; propodus pollex (fixed finger) broad, cutting edge with four medium teeth proximally, several small teeth distally; tips of both fingers touching when closed, enclosing long slim interspace; major chela propodus palm enlarged, swollen, propodus lower margin convex ( Fig. 9A ). Male left (minor) chela dactylus long, slim, gently curved, lined by small teeth; propodus pollex slim, slender, with four medium teeth proximately, rest lined by small teeth; tips of both fingers touching when closed enclosing long slim interspace; propodus palm slim, not enlarged (0.6 × height of major chela propodus palm), propodus elongated (as long as that of major chela), lower margin slightly concave ( Fig. 9B ). Cheliped merus stout, distinctly shorter than CW, medial inferior margin lined by small teeth, lateral inferior margin lined by granules; distal meral tooth small ( Fig. 9C, D ); cheliped carpus inner margin distal tooth large, pointed, proximal tooth extremely small, pointed ( Fig. 9C ); distal limb articles of ambulatory legs P2–5 (merus, carpus, propodus, dactylus) stout, not elongated; dactyli of P2–5 tapering to point, each bearing 4 rows of downward-pointing sharp bristles ( Fig. 7A ). Male pleon, telson together forming slim triangle, pleon edges slightly indented; telson triangular, apex rounded, base broadest, sides outwardly sloping; pleomeres PL1–6 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. 8B, C ). G1TA about 1/3 G1SA length (G1TA/G1SA 0.3), angled outward at 45° to longitudinal axis of G1SA; G1TA stout, cone-like with short setae along length, tapering to pointed tip ( Fig. 10A, B, D ). G1SA widest at base, narrowest at TA-SA junction; basal G1SA mesial margin lined by long setae; G1SA lateral margin smooth ( Fig. 10A, B ). G2SA ( Fig. 10C ) long, slim, subequal to G1SA; G2SA widest at base, tapering sharply inward about one-third along length, last two-thirds forming long, thin, tapering, upright process supporting long flagellum-like G2TA (G2TA/G2SA 0.62) ( Fig. 10C ). Size. Small-bodied species, adult between CWs 22.5–27.0 mm.

Color. The color of living specimens is unknown, but specimens preserved in ethanol are light brown.

Type locality. Tanzania, East Usambara Mountains , Bulwa (-5.583224, 37.507317) ( Fig. 11 ).

Distribution. This species is found in four localities in the East and West Usambara Mountains of Tanzania above 800 m ASL.

Habitat. Arcopotamonautes infravallatus and A. picus sp. nov. are both found in the montane habitats of the tropical cloud forests in the highlands of the East Usambara Mountains of northeastern Tanzania. The East and West Usambara Mountains are a biodiversity hotspot that lies between Mount Kilimanjaro and the coast and are part of the Eastern Arc Mountain range, a group of highlands in Tanzania that extend southward ending with the Udzungwa and Mahenge Mountains.Amani (the collection locality of both species) is now included in the Amani Nature Forest Reserve, a protected area in the Tanga Region of Tanzania. At Amani, A. infravallatus was collected from a tiny spring in an area with no surface water that had been cleared for cultivation but subsequently covered with ground vegetation. Crabs were taken either from their holes dug in mud or from under stones.

Remarks. Identification of specimens assigned to A. infravallatus was based on comparisons with the adult male type of Telphusa infravallata Hilgendorf, 1898 (CW 23.4, CL 15.4, CH 7.4, FW 6.5 mm) (ZMB 11378) in the Museum für Naturkunde, Berlin, Germany. Rathbun (1905) and Chace (1942) both recognized this species but each reassigned it to a different genus, Potamon (Potamonautes) and Potamon respectively. Bott (1955) synonymized T. infravallata with Potamon (Potamonautes) usambarae Rathbun, 1933 , and this is accepted here, following comparison of T. infravallata with the adult male cotype of P. (P.) usambarae from Amani in the Usambara Mountains (CW 22.8 mm) (MCZ 7680). Subsequent authors ( Reed & Cumberlidge 2006; Ng et al. 2008) treated this species as Potamonautes infravallatus , and Cumberlidge & Daniels (2022) treated it as Arcopotamonautes infravallatus . Chace (1942) recognized Potamon usambarae and Thelphusa infravallata as two separate species, but that opinion is not followed here. In addition, several authors ( Balss 1929, 1936; Bott 1955) included A. infravallatus as a junior synonym of A. johnstoni ( Miers, 1885) , a large species from Mt. Kilimanjaro, Tanzania, but this is not recognized here.

In the present work, two lots of specimens from the West Usambara Mountains (NMU TRW1970.09; TRW1966.12b) previously assigned to A. xiphoidus Reed & Cumberlidge (2006) were identified here as belonging to A. infravallatus following comparison with the holotype of A. xiphoidus . In addition, two lots of specimens from Amani, East Usambara Mountains (NMU TRW1967.11 and NMU TRW1975.01) previously assigned to A. infravallatus by Reed & Cumberlidge (2006) were identified as belonging to A. xiphoidus Reed & Cumberlidge, 2006 following comparison with the holotype of A. xiphoidus .

Comparisons. The genus Arcopotamonautes ( Bott, 1955) currently comprises 17 species from the D. R. Congo, Kenya, Malawi, Rwanda, Tanzania, and Zambia ( Cumberlidge & Daniels 2022; Cumberlidge & Jonas 2024). Arcopotamonautes picus sp. nov. and A. infravallatus are assigned to this genus because they conform to the diagnosis provided by Cumberlidge & Daniels (2022: 1291). For example, in both species the postfrontal crest is distinct and completely traverses the carapace, the epibranchial tooth is reduced to a small granule, and the posterior carapace sulci are all distinct ( Figs. 1A, B , 7A, B ).

Arcopotamonautes picus sp. nov. and A. infravallatus can be distinguished from A. suprasulcatus ( Hilgendorf, 1898) and A. bellarussus ( Daniels, Phiri & Bayliss, 2014) by the form of the G1TA, which is slim and cone-shaped in A. picus sp. nov. ( Fig. 4A–C ) and stout and cone-shaped in A. infravallatus ( Figs. 6C , 10A, B, D ) (versus slim, curved, and needle-like in A. suprasulcatus and A. bellarussus (see Daniels et al. 2014: fig. 5A, B)). Arcopotamonautes picus sp. nov. and A. infravallatus can be distinguished from A. xiphoidus ( Reed & Cumberlidge, 2006) by the form of the G1TA, which is has a tuft of long setae proximally in A. picus sp. nov. ( Fig. 4A–C ) and short setae all along its length in A. infravallatus ( Figs. 6 C , 10A, B, D ) (versus a G1TA that lacks setae in A. xiphoidus (see Reed & Cumberlidge 2006: figs. 171–172)). Arcopotamonautes picus sp. nov. and A. infravallatus 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 smooth and lacks teeth in A. picus sp. nov. ( Fig. 1A, B ) and A. infravallatus ( Figs. 5A , 7A, B ) (versus a carapace lateral margin that has several teeth behind the epibranchial tooth in A. orbitospinus (see Reed & Cumberlidge 2006: pl. V, A, B; fig. 42 (as Potamonautes lirrangensis ), and A. platynotus (see Reed & Cumberlidge 2006: fig. 94)). Arcopotamonautes picus sp. nov. and A. infravallatus 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 small but pointed in A. picus sp. nov. ( Fig. 3D ) and A. infravallatus ( Figs. 6D , 7A , 9C ) (versus extremely broad and blunt in A. platycentron (see Reed & Cumberlidge 2006: figs. pl. IX, A)). Arcopotamonautes picus sp. nov. can be distinguished from A. unisulcatus ( Rathbun, 1933) by the sulci on the anterior thoracic sternum, where the S3/4 is distinct and completely traverses the thoracic sternum in A. picus sp. nov. ( Fig. 2B ) (versus a S3/4 that is deep at sides and obscure in the middle in A. unisulcatus (see Reed & Cumberlidge 2006: fig. 130)). Arcopotamonautes picus sp. nov. can be distinguished from A. amosae ( Cumberlidge, Johnson, Clark & Genner, 2021) , A. caputanatis ( Cumberlidge, Fastiggi & Clark, 2019) , A. johnstoni ( Miers, 1885) , A. raybouldi ( Cumberlidge & Vannini, 2004) , A. gerdalensis ( Bott, 1955) and A. montivagus ( Chace, 1953) by the form of the G1TA, which comprises low dorsal and ventral lobes and lacks a distinct crest in A. picus sp. nov. ( Fig. 4A, B, D, E ) and A. infravallatus ( Fig. 10A, B, D ) (versus a G1TA where the dorsal lobe and/or ventral lobe has a distinct raised rounded crest in A. amosae , A. caputanatis , A. johnstoni (see Reed & Cumberlidge 2006: figs. 151, 152), A. raybouldi (see Reed & Cumberlidge 2006: figs. 165, 166), A. gerdalensis (see Reed & Cumberlidge 2006: figs. 147, 148), and A. montivagus (see Chace 1953: fig. 3e–g, j)).

Arcopotamonautes picus sp. nov. can be distinguished from A. infravallatus by the sulci on the anterior thoracic sternum, where the S3/4 is distinct and completely traverses the thoracic sternum in A. picus sp. nov. ( Fig. 2B, C ) (versus a S3/4 that is U-shaped, distinct at margins and faint in the middle in A. infravallatus ; Figs. 5B, C , 8B, C ); by the margins of thoracic sternite S4, which are low in A. picus sp. nov. ( Fig. 2B, C ) (versus distinctly raised and thickened in A. infravallatus ; Figs. 5B, C , 8B, C ); by the inferior margins of the cheliped merus which are each lined by large teeth in A. picus ( Fig. 3C, D ) (versus cheliped merus inferior margins lined by small faint granules in A. infravallatus ; Figs. 6C, D , 9C, D ); and by the G1TA which is a slim cone with a tuft of long setae proximally in A. picus sp. nov. ( Fig. 4A, B, D–F ) (versus a G1TA which is a stout cone with short setae all along its length in A. infravallatus ; Figs. 6E , 10A, B, D ).

Figures

FIGURE 1. Arcopotamonautes picus sp. nov., adult ♂ holotype CW 15.6 mm, from Amani Area, East Usambara Mountains, Tanzania (NMU 1964.03A). A, whole animal, dorsal view; B, carapace dorsal view. Scale bars: A = 6.0 mm; B = 2.1 mm.

FIGURE 2. Arcopotamonautes picus sp. nov., adult ♂ holotype CW 15.6 mm, from Amani Area, East Usambara Mountains, Tanzania (NMU 1964.03A). A, carapace, frontal view; B, cephalothorax showing anterior thoracic sternum, ventral view; C, cephalothorax showing pleon and posterior thoracic sternum, ventral view. Scale bars: A = 2.1 mm; B, C = 2.7 mm.

FIGURE 3. Arcopotamonautes picus sp. nov., adult ♂ holotype CW 15.6 mm, from Amani Area, East Usambara Mountains, Tanzania (NMU 1964.03A). A, right chela, frontal view; B, left chela, frontal view; C, left cheliped merus, ventral view; D, left cheliped carpus and merus, ischium, dorsal view; E, third maxilliped, frontal view; F, mandible palp, turned to show ridge on terminal article of mandibular palp. Scale bars: A, B = 3.6 mm; C, D, E = 1.3 mm; F = 1.0 mm.

FIGURE 4. Arcopotamonautes picus sp. nov., adult ♂ holotype CW 15.6 mm, from Amani Area, East Usambara Mountains, Tanzania (NMU 1964.03A). A, left G1, ventral view; B, left G1, dorsal view; C, left G2, ventral view; D, left G1TA, superior view; E, left G1, ventral view, detail of terminal article (G1TA); F, left G1, dorsal view, detail of terminal article (G1TA). Scale bars: A, B = 1.0 mm; C = 0.8 mm; D, E, F = 0.4 mm.

FIGURE 5. Telphusa infravallata Hilgendorf, 1898, holotype adult ♂ CW 23.4 mm, from Buloa (=Bulwa), East Usambara Mountains, Tanzania (ZMB 11378). A, carapace, dorsal view; B, carapace frontal view; C, cephalothorax showing anterior thoracic sternum, ventral view. Scale bars: A, B = 3.4 mm.

FIGURE 6. Telphusa infravallata Hilgendorf, 1898, holotype adult ♂ CW 23.4 mm, from Buloa (=Bulwa), East Usambara Mountains, Tanzania (ZMB 11378).A, right chela, frontal view; B, left chela, frontal view; C, left cheliped merus, ventral view; D, left cheliped carpus and merus, ischium, dorsal view; E, gonopods in situ with pleon pulled back. Scale bars:A, B = 6.7 mm; C, D = 4.0 mm; E = 2.6 mm.

FIGURE 7. Arcopotamonautes infravallatus (Hilgendorf, 1898), adult ♂ CW 25.6 mm, from Amani Area, East Usambara Mountains, Tanzania (NMU TRW1970.09). A, whole animal, dorsal view; B, carapace dorsal view. Scale bars: A = 7.6 mm; B = 3.4 mm.

FIGURE 8. Arcopotamonautes infravallatus (Hilgendorf, 1898), adult ♂ CW 25.6 mm, from Amani Area, East Usambara Mountains, Tanzania (NMU TRW1970.09). A, carapace, frontal view; B, cephalothorax showing anterior thoracic sternum, ventral view; C, cephalothorax showing pleon and posterior thoracic sternum, ventral view. Scale bars: A = 3.4 mm; B = 4.2 mm; C = 4.0 mm.

FIGURE 9. Arcopotamonautes infravallatus (Hilgendorf, 1898), adult ♂ CW 25.6 mm, from Amani Area, East Usambara Mountains, Tanzania (NMU TRW1970.09). A, right chela, frontal view; B, left chela, frontal view; C, left cheliped, carpus, merus, ischium, dorsal view; D, left cheliped, merus, ischium, ventral view; E, third maxilliped, frontal view; F, mandible, frontal view; G, mandibular palp, turned to show detail. Scale bars: A, B = 6.7 mm; C = 4.4 mm; D = 4.0 mm; E = 1.3 mm; F = 1.0 mm; G = 0.8 mm.

FIGURE 10. Arcopotamonautes infravallatus (Hilgendorf, 1898), adult ♂ holotype CW 25.6 mm, from Amani Area, East Usambara Mountains, Tanzania (NMU TRW1970.09).A, left G1, ventral view; B, left G1, dorsal view; C, left G2, ventral view; D, left G1TA superior view. Scale bars: A = 1.0 mm; B = 0.7 mm; C = 1.0 mm; D = 0.4 mm.

FIGURE 11. Map showing the geographic distribution of Arcopotamonautes picus n. sp and A. infravallatus (Hilgendorf, 1898). Black square = both species found at same locality (Amani); black circles = additional localities for A. infravallatus (Hilgendorf, 1898). Scale bar = 25 km. See text for exact localities.