Arcopotamonautes montivagus (Chace, 1953)

Arcopotamonautes montivagus View in CoL s.s. (Chace)

( Figures 2 View Figure 2 , 9–14 View Figure 9 View Figure 10 View Figure 11 View Figure 12 View Figure 13 View Figure 14 , Tables 1–3)

Potamon ( Potamonautes) montivagus Chace 1953: 435–441 , Figures 3 View Figure 3 and 4 View Figure 4 .

Potamon ( Potamonautes) montivagus Bott 1955: 265 , not junior synonym of ( Lirrangopotamonautes) johnstoni View in CoL johnstoni (Miers, 1885) View in CoL .

Potamonautes montivagus Reed and Cumberlidge 2006: 1262 View in CoL ; Ng et al. 2008: 171.

Arcopotamonautes montivagus Cumberlidge and Daniels 2022: 1294 View in CoL , table 3.

Material examined

Type material. Holotype: MALAWI: adult ♂ (CW 65.5, CL 44.2 mm, CH 21.8 , FW 16.6 mm), Cholo

Cholo District ( 16.076°S, 035.050°E) coll GoogleMaps . A GoogleMaps . Loveridge, 26 March 1949 ( MCZ 12611 About MCZ ) .

Other material. MALAWI: 3 subadult ♂♂ (CWs 25.2 mm to 49.5 mm), 2 subadult ♀♀ (CWs 37.5, 42.9 adult ♂♂ (CWs 57.7, 67.6 mm), 8 adult ♀♀ (CWs 51.5 to 67.9 mm), Zomba District (( 15.4991°S

coll. E . Lawrence, 28 June 1938 ( NHM 1938.6.28.9–16) . MALAWI: subadult ♂ (CW 48.5 mm), adult 50.4 mm), Mulunguzi near Zomba ( 15.3798°S 035.3340°E), coll GoogleMaps . R. C. H. Sweeney , December 1963 1969.893 ). MALAWI: 2 subadult ♂♂ (CWs 47.5, 34.2 mm), Nkhata Bay ( 11.6026°S 034.2951°E), coll GoogleMaps .

1956 ( NHM 1956.65.9). MALAWI: subadult ♀ (CW 25.8 mm), Zomba ( 15.3844°S 035.3420°E, 610–914 GoogleMaps

coll. H. H . Johnston, 2 February 1894 ( NHM 1894.2.2.1) . MALAWI: subadult ♂ (CW 42.1 mm), subadult

44 mm), Mulanje, stream flowing through Tea Estate ( 16.027°S, 35.517°E) coll GoogleMaps . G GoogleMaps . Fryer , 5 June 1956 1956.6.5.7–8 ). MALAWI: 2 adult ♀♀ (CWs 64.9, 56.3 mm), 3 subadult ♀♀ (CWs 26.1 to 35.4 mm), 7

♂♂ (CWs 15.3 to 27.7 mm), juvenile ♂ (CW 10.6 mm), coll . D . J . Lewis, January 1960 ( NHM 2011.1522 MALAWI: subadult ♀ (CW 43 mm), Magombo ( 14.991°S, 34.951°E), coll. D. J. Lewis ( NHM MALAWI: subadult ♀ (CW 33.2 mm), Rukuru River flowing into the western shore of Lake Malawi ( GoogleMaps

S, 34.262°E), coll . A . J. Davy and W. S . Atkins, 2011 ( NHM 2011.1510 ); MALAWI: 3 subadult ♀♀ (CWs

HISTORY

Diampwe River , Central Province ( 14.136°S, 34.088°E), coll GoogleMaps . G GoogleMaps . Fryer, 5 June 1956 ( NHM 1956.6.5.4 MALAWI: subadult ♀ (CW 24.6 mm), subadult ♂ (CW 23 mm), 5 April 1952 ( NHM 1952.4.5.1); northern Malawi, subadult ♀ (CW 30.4 mm), subadult ♂ (CW 42.2 mm), coll . Sir H . H . Johnson , 29 April ( NHM 1897.4.29.2–3); MALAWI: 2 juvenile ♂♂ (CW 15.7 mm ( NHMUK 2025.1128 About NHMUK ), 18.9 mm (2025.1129), subadult ♀ (CW 33.0 mm ( NHMUK 2025.1130 About NHMUK ), Matsimbe 14.186°S, 33.672° M. J. Genner, 10 June 2010; MALAWI: subadult ♂ (CW 36.5 mm, Mikolongwe ( 15.886°S, 35.200 M. J. Genner, 17 May 2010 ( NHMUK 2025.1136 About NHMUK ); MALAWI: 3 subadult ♂♂ (CWs 34.3 mm ( NHMUK

16.6 mm ( NHMUK 2025.1132 About NHMUK ), 22.9 mm ( NHMUK 2025.1134 About NHMUK ) 2 subadult ♀♀ (CWs 21.5 mm (2025.1133), 22.1 mm ( NHMUK 2025.1135 About NHMUK ), Domasi ( 15.304°S, 35.372°E) coll. M. J. Genner, 15 May TANZANIA: 12 adult ♂♂, CWs in mm (CW 60.2 ( NHMUK 2025.1150 About NHMUK ), CW 58.0 ( NHMUK 2025.1152 About NHMUK ), ( NHMUK 2025.1148 About NHMUK ), CW 56.4 ( NHMUK 2025.1143 About NHMUK ), CW 55.6 ( NHMUK 2025.1153 About NHMUK ), CW 54.9 (2025.1142), CW 54.3 ( NHMUK 2025.1160 About NHMUK ), CW 52.5 ( NHMUK 2025.1149 About NHMUK ), CW 52.4 ( NHMUK 2025.1147 About NHMUK 51.8 ( NHMUK 2025.1157 About NHMUK ), CW 50.9 ( NHMUK 2025.1162 About NHMUK ), CW 50.2 ( NHMUK 2025.1166 About NHMUK ), 12 adult ♀♀ GoogleMaps

in mm (CW 62.5 ( NHMUK 2025.1165 About NHMUK ), CW 61.8 ( NHMUK 2025.1155 About NHMUK ), CW 58.0 ( NHMUK 2025.1144 About NHMUK ), ( NHMUK 2025.1156 About NHMUK ), CW 57.2 ( NHMUK 2025.1151 About NHMUK ), CW 56.0 ( NHMUK 2025.1164 About NHMUK ), CW 55.7 (2025.1163), CW 55.4 ( NHMUK 2025.1158 About NHMUK ), CW 55.4 ( NHMUK 2025.1161 About NHMUK ), CW 55.1 ( NHMUK 2025.1154 About NHMUK 54.0 ( NHMUK 2025.1159 About NHMUK ), CW 53.5 ( NHMUK 2025.1141 About NHMUK ); subadult ♀ CW 45.2 mm ( NHMUK subadult ♂ CW 43.1 mm ( NHMUK 2025.1145 About NHMUK ) River Mwalalo ( 9.480°S, 34.033°E), coll. P. N. GoogleMaps

16 November 2020; TANZANIA: subadult ♂ (CW 38.4 mm), coll . J . Kingdon, November 1989 ( NMU XI.1989) . MALAWI: subadult ♂ (CW 45.2 mm), adult ♀ (CW 53 mm), Muloza West , Cholo area ( 35.761°E), coll . M . J. Roberts, 15 September 1988 ( NMU 15.09.1988) . ZAMBIA: 2 subadult ♀♀ (CW ( NHMUK 2025.1138 About NHMUK ), CW 26 mm ( NHMUK 2025.1140 About NHMUK ), 2 subadult ♂♂ (CW 29.0 mm ( NHMUK

24.0 mm ( NHMUK 2025.1137 About NHMUK ), Chipata ( 13.656°S, 32.655°E), coll GoogleMaps . M GoogleMaps . J. Genner, 20 June 2010.

subadult ♂ (CW 46.5 mm), Inyanga , from River Mare in the Eastern Highlands ( 18.213°S, 1,700 –1,829 m ASL) near government trout hatchery, coll GoogleMaps . T. R. Williams, 7 March 1972 ( NMU 7 .III MOZAMBIQUE: subadult ♂ (CW 45.2 mm), coll. H. B. Cott, 5 March 1929 ( NHM 1929.3.5.14–15).

Diagnosis

Based on holotype. Exorbital tooth small, low; epibranchial tooth small, granular; anterolateral carapace by granules ( Figures 9 View Figure 9 (a,b), 10(a,b), 11(a,b) and 12(a,b)); carapace lateral margin posterior to tooth lined with granules, curving strongly inward posteriorly over carapace surface ( Figures 9 View Figure 9 (a) and 12(a)); postfrontal crest distinct, lined by granules, completely traversing carapace between teeth; posterior surface of carapace with deep urogastric, cardiac grooves ( Figures 9 View Figure 9 (a) and 11(a)); branchiostegite suborbital region with granules on surface, subhepatic region with granules,

surface, branchiostegite suborbital region with granules on surface, subhepatic region with granules,

on surface, pterygostomial region smooth except for line of granules close to granular epimeral ( Figures 10 View Figure 10 (b) and 12(b)). Third maxilliped ischium with deep vertical sulcus ( Figure 12 View Figure 12 (e)); thoracic sulcus S3/4 reduced to two short deep sulci, middle part obscure ( Figures 9 View Figure 9 (b) and 11(b,c)); dactylus, propodus pollex of both chelae lined by distinct rounded teeth, 3 large teeth proximally chela fixed finger with 3 large rounded teeth proximally, interspersed by medium rounded teeth (Figure d)); cheliped carpus inner margin distal tooth large, slim, pointed, proximal tooth very small, ( Figure 10 View Figure 10 (c,d) and 11(a)); cheliped merus lower margins lined by large granules, distal meral tooth like ( Figure 10 View Figure 10 (c,d) and 12(f,g)); P5 carpus, propodus, and dactylus not elongated ( Figure 11 View Figure 11 (a)) midpart raised by thin high dorsal crest formed from medial margin of dorsal lobe ( Figure 7 View Figure 7 (a,b midpart broadened by long wide gutter running between medial, lateral margins of dorsal lobe ( Figure G1 View Figure 1 TA distal third slim, ventral, dorsal lobes low, tapering to pointed upcurved tip ( Figures 13 View Figure 13 (a,b) and f)); horizontal margin on G1 ventral side at G1TA-G1SA junction ( Figures 13 View Figure 13 (a) and 14(f)); U-shaped tion filled with conspicuous dorsal membrane on G1SA dorsal side ( Figure 14 View Figure 14 (a–c)); margins of G1TA lined by setae ( Figure 13 View Figure 13 (a,b)).

HISTORY

d = 25.3 mm; e = 14.2 mm.

granules ( Figures 9 View Figure 9 (a,b), 10(a,b), 11(a,b) and 12(a,b)); carapace lateral margin posterior to epibranchial lined by granules, curving strongly inward posteriorly over carapace surface ( Figures 9 View Figure 9 (a), 11(a) and postfrontal crest distinct, lined by granules, completely traversing carapace between epibranchial posterior surface of carapace with deep urogastric, cardiac grooves ( Figures 9 View Figure 9 (a), 10(a), 11(a) and carapace branchiostegite suborbital region with granules on surface, subhepatic region with carinae on surface, branchiostegite suborbital region with granules on surface, subhepatic region granules, carinae on surface, pterygostomial region smooth except for line of granules close to epimeral suture ( Figures 10 View Figure 10 (b) and 12(b)). Epistomial tooth prominent, granulated, V-shaped (Figures and 12(b)). Mandibular palp consisting of basis plus two articles; terminal article simple, undivided, lobe or ridge at junction between articles ( Figure 13 View Figure 13 (d–f)). Third maxilliped ischium with deep vertical ( Figure 12 View Figure 12 (e)); thoracic sternal sulcus S3/4 reduced to two short deep sulci, middle part obscure (Figures and 11(b,c)); episternal sulci S4/E4 obscure, S5/E5, S6/E6, S7/E7 faint, incomplete ( Figures 9 View Figure 9 (b) and Major chela dactylus (moveable finger), propodus pollex (fixed finger) thick, broad, leaving long thin space between fingers when closed; margins of dactylus, propodus pollex of both chelae lined by rounded teeth margins of both fingers lined by distinct rounded teeth, three large teeth ( Figure 10 View Figure 10 (c,d)); cheliped carpus inner margin distal tooth large, slim, pointed, proximal tooth small, ( Figures 10 View Figure 10 (c,d) and 11(a)); cheliped merus lower margins lined by large granules, distal meral tooth like ( Figures 10 View Figure 10 (c,d) and 12(f,g)); P5 carpus, propodus, and dactylus not elongated ( Figure 11 View Figure 11 (a)); P3

HISTORY e = 2.0 mm; f = 2.0 mm.

telson narrow triangle with rounded apex, pleomeres PLl–6 quadrate (Figure (11(b,c)). G1TA length one-third G1SA length (G1TA/G1SA 0.4), angled outward at 45° to longitudinal axis of G1SA; lateral G1TA lined by short setae; G1TA ventral lobe low, not raised, not widened, extending from G1 junction to G1TA tip; G1TA slim basally, dorsal, ventral lobes both low, not widened ( Figures 13 View Figure 13 (a,b) (a–f)); G1TA midpart higher, wider; height due to dorsal crest formed from thin, high medial margin of lobe (( Figures 13 View Figure 13 (a,b) and 14(a–f)); G1TA midpart width due to wide gutter running longitudinally medial, lateral margins of dorsal lobe ( Figure 14 View Figure 14 (d)); G1TA distal third slim, ventral, dorsal lobes low,

to pointed upcurved tip ( Figures 13 View Figure 13 (a,b) and 14(a–f)); horizontal margin on G1 ventral side at G1

HISTORY to G1SA; G2SA widest at base, tapering sharply inward about one-third along length, last two-thirds long, thin, tapering, upright process supporting long flagellum-like G2TA (G2TA/G2SA 0.6) (Figure

Size

Large species, adult size range between CW 50 to 67 mm.

Colour

The carapace, ambulatory legs and claws of living specimens range from green-brown to

Preserved specimens are uniformly light brown ( Figures 9 View Figure 9 (a) and 11(a)).

Distribution

Arcopotamonautes montivagus s.s. occurs in Tanzania, East Africa and in four neighbouring countries ( Mozambique, Zambia, and Zimbabwe) in southern Africa ( Figure 2 View Figure 2 ). Notably, this species is reported Rungwe Mountains in southern Tanzania and in the rivers draining south from there into the north Zomba, and Cholo mountain). This river-living species has never been collected in Lake Malawi.

a few reports of A. montivagus s.s. from Mozambique, Zambia, and Zimbabwe ( Figure 2 View Figure 2 ).

Comparisons Arcopotamonautes itamba and A. montivagus are morphologically similar as would be expected of of a species complex. Comparisons of a number of morphometric characters based on the dimensions carapace and pereiopods P1–5 of these two species found only minor differences between them ( et al. 2024: figs 3A, 4B). Morphological characters shared by A. itamba and A. montivagus include distal and proximal teeth on the inner margin of the cheliped carpus; a pointed distal meral tooth cheliped merus; a major chela with an arched dactylus; a complete and distinct postfrontal crest grooves on the posterior surface of the carapace; a low exorbital tooth with a granulated margin; a sized epibranchial tooth; a carapace lateral margin that is either smooth or has fine granulations; maxilliped ischium with a deep vertical sulcus; a sternal sulcus S3/4 that is deep at the sides and the centre, a G1TA with a conspicuous thin high dorsal crest on the medial margin of the dorsal a G1TA that terminates in an upcurved tip.

Arcopotamonautes itamba can be distinguished from A. montivagus by smooth carapace branchiostegite suborbital, subhepatic, pterygostomial regions ( Figures 3 View Figure 3 (b), 4(b) and 5(a)) (vs fields of granules and in the branchiostegite suborbital and subhepatic regions, and a smooth pterygostomial region (a line of granules parallel to the granulated epimeral suture) in A. montivagus ( Figures 9 View Figure 9 (b), 10(a,b), 11 12(a,b)) and by the elongated P5 ambulatory leg segments in A. itamba ( Figure 3 View Figure 3 (a,b)) (vs the ambulatory leg segments in A. montivagus ( Figure 11 View Figure 11 (a)). These two taxa have distinct and non-overlapping geographical distributions ( Figures 1 View Figure 1 and 2 View Figure 2 ), although specimens of A. montivagus and A. itamba have reported to occur less than 30 km apart in southern Tanzania, from the Mwalalo and Mguwusi respectively.

Arcopotamonautes montivagus and A. itamba are both found mainly in the rivers and lakes of Malawi drainage, and both share some morphological characters with A. orbitospinus , the Malawi endemic to Lake Malawi. Characters shared by these three taxa include two spines on the inner margin cheliped carpus (distal tooth larger than proximal tooth), a pointed distal meral tooth on the cheliped and a major chela with an arched dactylus. Additional characters shared by these two species A. orbitospinus include a complete and distinct postfrontal crest, deep grooves on the posterior the carapace, an exorbital tooth with a granulated margin, a deep vertical sulcus on the ischium of maxilliped, a G1TA with a conspicuous thin high dorsal crest on the medial margin of the dorsal a G1TA whose slim tapering distal third terminates in an upcurved tip.

Arcopotamonautes itamba View in CoL and A. montivagus View in CoL can be distinguished from other species of freshwater that occur in southern Tanzania, northern Malawi, and northern Zambia including the two lake-living A. orbitospinus View in CoL from Lake Malawi and A. platynotus (Cunnington, 1907) View in CoL from Lake Tanganyika. In A. ( Figures 3 View Figure 3 and 4 View Figure 4 ) and A. montivagus View in CoL ( Figure 9 View Figure 9 (a)) the carapace lateral margin is smooth and lacks a carapace lateral margin that has several teeth behind the epibranchial tooth in A. orbitospinus Cumberlidge et al. 2012 View in CoL , fig. 4A,E (as Potamonautes lirrangensis View in CoL ), and A. platynotus View in CoL , cf. Reed Cumberlidge 2006, fig. 94).

Arcopotamonautes itamba View in CoL and A. montivagus View in CoL can be distinguished from the river-living A. suprasulcatus ( Hilgendorf, 1898) View in CoL and A. bellarussus (Daniels, Phiri and Bayliss, 2014) View in CoL by the form G1TA. The midpart is distinctly widened and raised up by a thin high crest in A. itamba View in CoL ( Figures 7 View Figure 7 (a,b,d (a,b,d,e)) and A. montivagus View in CoL ( Figures 13 View Figure 13 (a,b) and 14(a–f)) (vs a slim and curved G1TA in A. suprasulcatus Reed and Cumberlidge 2006 View in CoL , figs 167, 168, and A. bellarussus View in CoL , cf. Daniels et al. 2014, fig. Arcopotamonautes itamba View in CoL and A. montivagus View in CoL can be distinguished from Maritimonautes obesus (H Edwards, 1868) View in CoL , M. choloensis ( Chace, 1953) View in CoL , and Potamonautes bayonianus (Brito Capello, 1864) View in CoL . The of the third maxilliped possesses a deep vertical sulcus in A. itamba View in CoL ( Figures 5 View Figure 5 (a)) and A. montivagus View in CoL (11(b) and 12a)) (vs a third maxilliped ischium that lacks a distinct vertical sulcus in M. obesus View in CoL , M. and P. bayonianus View in CoL ). Finally, A. itamba View in CoL and A. montivagus View in CoL can be distinguished from A.

HISTORY

A. montivagus ( Figures 5 View Figure 5 (a,b) and 11(b,c)) (vs a complete and deep S3/ 4 in A. caputanatis cf.

et al. 2019, fig. 1B, and in P. mulanjeensis cf. Daniels and Bayliss 2012, fig. 5B).

Remarks

Bott (1955) treated Potamon ( Potamonautes) montivagus Chace as a junior synonym of Arcopotamonautes johnstoni (Miers) . This, however, was not accepted by subsequent authors, such as Reed and

(2006), following their comparison of the holotype of P. ( P.) montivagus ( MCZ 12611 About MCZ ) with the

Thelphusa depressa var. johnstoni Miers (NHM 1885.2). This present study agrees with Reed and

(2006), Ng et al. (2008), and Cumberlidge and Daniels (2022) that A. montivagus s.s. is a valid species rejects Bott’s (1955) opinion that this taxon is a junior subjective synonym of A. johnstoni (Miers, 1885

Habitat

Arcopotamonautes montivagus s.s. is found in rivers or shallow-lake environments proximate to Lake with the closest specimen to the lake from the River Mwalalo, about 2 km upstream from Matema

Malawi ( Figure 2 View Figure 2 ). It has also been recorded in rivers in Zambia, Zimbabwe and Mozambique. This species has never been collected in Lake Malawi, while the Lake Malawi species A. orbitospinus is

Lake Malawi and has never been reported from rivers or streams ( Cumberlidge et al. 2012). The stout P2–5 ambulatory leg segments of A. montivagus s.s., a river-living species ( Figure 11 View Figure 11 (a)), may adaptation for better locomotion between the rocky beds of fast-flowing rivers and streams.

Conservation status

Arcopotamonautes montivagus s.s. was most recently assessed for the IUCN Red List of Threatened

2018 (as A. montivagus s.l.), and listed as Least Concern (LC) ( Cumberlidge 2018). This was a change previous assessment in 2008 when it was initially listed as VU but this species was later downlisted to LC based on recent collections of specimens from new localities in five different countries ( Figure 2 View Figure 2 collections expanded the number of localities from seven to 18, and increased the number of countries this species from one ( Malawi) to five (with the addition of Tanzania, Mozambique, Zimbabwe, and

The present division of A. montivagus s.l. into two taxa ( A. montivagus s.s. and A. itamba sp. n.) does not the extinction risk assessment of A. montivagus s.s. because only a few specimens of A. montivagus s transferred to A. itamba sp. n. and the EOO of A. montivagus s.s. ( 557,115 km 2) remains well threshold for LC.

Arcopotamonautes montivagus s.s. occurs in three protected areas, where its habitat is unlikely disturbed: in Zimbabwe (Rhodes Inyanga National Park), Malawi ( Mulanje Mountain Forest Reserve Tanzania (Uwanda Game Reserve). Arcopotamonautes montivagus s.s. is not collected for food, and no known current threats.

Updated checklists

The addition of the new species in this work means that the updated freshwater crab checklist for

( Table 1) comprises 32 species, five genera, and two families ( Hilgendorf 1898; Rathbun 1933; Chace

Bott 1955; Reed and Cumberlidge 2006; Gereau et al. 2016; Cumberlidge et al. 2012; Cumberlidge Daniels 2022; Cumberlidge and Conners 2024; Cumberlidge and Jonas 2024). Four of these genera are African family Potamonautidae Bott 1970 ( Arcopotamonautes Bott, 1955 ; Platythelphusa A. Milne-Edwards 1887 ; Rotundopotamonautes Bott, 1955 ; and Maritimonautes ; Cumberlidge and Daniels, 2022), while genus, Deckenia Hilgendorf, 1869 , is in the Afrotropical family Deckeniidae Ortmann, 1897 (Cumberlidge Daniels, 2022).

The updated freshwater crab checklist for Malawi ( Table 2) comprises seven species: Arcopotamonautes Bott, 1955 ; two in Maritimonautes Cumberlidge and Daniels, 2022 , and Potamonautes MacLeay, 1838 . All three genera are assigned to the Potamonautidae Bott, 1970

1953; Cumberlidge and Daniels 2022).

The updated freshwater crab checklist for Zambia ( Table 3) comprises 12 species: