Arcopotamonautes parekeeae, Cumberlidge & Jonas, 2024

Cumberlidge, Neil & Jonas, Gabrielle I., 2024, Two new freshwater crab species from the Eastern Arc Mountains, Tanzania, East Africa (Brachyura: Potamoidea: Potamonautidae), Zootaxa 5476 (1), pp. 51-65 : 52-57

publication ID	https://doi.org/ 10.11646/zootaxa.5476.1.8
publication LSID	lsid:zoobank.org:pub:E32A2F95-E4E8-4F3C-BDBF-831E9F8C98BE
DOI	https://doi.org/10.5281/zenodo.12681536
persistent identifier	https://treatment.plazi.org/id/CE0E4F1A-FFDF-490D-6BF5-874778C2F923
treatment provided by	Plazi
scientific name	Arcopotamonautes parekeeae
status	sp. nov.

Treatment

Arcopotamonautes parekeeae View in CoL n. sp.

( Figs. 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 , 11 View FIGURE 11 )

Type material. Holotype: NMU 1968.02a , adult male (CW 39.0, CL 25.2, CH 12.0, FW 11.0 mm; P1R chela propodus length 37.0 mm), Tanzania, South Pare Mountains , Yongoma River, 13 km south of Gonja, 579 m ASL, 1.6 km north of bridge at Ndungu (-4.367653°, 38.047267°), coll. J. N. Raybould, 12–15 May 1968 GoogleMaps . Paratypes: NMU 1968.02b , adult male (CW 34.8, CL 23.6, CH 11.0, FW 11.0 mm); adult male (CW 36.8 mm), adult female (CW 36.6 mm), subadult female (CW 27.7 mm), same details as holotype GoogleMaps .

Other material examined. NMU EA 62.29 , adult male (CW 27.5, CL 18.7, CH 10.7, FW 8.5 mm), Tanzania, South Pare Mountains , about 1.6 km uphill from the rest house at Gonja (1,192 m ASL) (-4.263889°, 38.011111°), coll. J. N. Raybould, 14 February 1962 GoogleMaps . NMUTRW EA.62.35 , adult male (CW 26.8, CL 17.8, CH 8.6, FW 7.8 mm), adult male (CW 26.7 mm), 5 subadult males (not measured), adult female (CW 28.6, CL 18.2, CH 9.1, FW 8.2 mm), 5 adult females (CWs 31.0, 29.5, 28.9, 28.0, 27.8 mm), 2 subadult females (CWs 27.2, 25.0 mm), 6 females (CWs ~ 20 mm), 3 juveniles (CWs ~ 10 mm), South Pare Mountains , 2 to 3 km northwest of Vumari Mission (897 m ASL) (-3.919987°, 37.791830°) about 16 km northeast of the town of Same. Coll. T. R. Williams, 18 February 1962 .

Diagnosis. Exorbital tooth small, blunt ( Fig. 1A, B View FIGURE 1 ); anterior; posterior male thoracic sternum surface completely smooth ( Fig. 2B, C View FIGURE 2 ); inferior margins of cheliped merus with four large well-separated teeth, distal meral tooth large ( Fig. 3C, D View FIGURE 3 ); cheliped carpus inner margin distal tooth medium sized, blunt, proximal tooth small, pointed, otherwise margin smooth ( Fig. 3E View FIGURE 3 ); dactylus of male right (major) chela distinctly arched with three well-spaced medium teeth interspersed by granule-like teeth ( Fig. 3A View FIGURE 3 ); G1TA widened basally; in three parts, ventral lobe low, dorsal lobe in two parts, high rounded crest medially, low lobe laterally, ventral lobe lined by long setae ( Figs. 4A–C View FIGURE 4 , 5B, C View FIGURE 5 ).

Description. Carapace surface smooth, widest in anterior third (CW/FW = 3.2), medium height ( CH /FW = 1.1) ( Figs. 1A, B View FIGURE 1 , 2A View FIGURE 2 ), semi-circular, urogastric grooves deep; cardiac region weakly marked, cervical grooves short, faint; transverse branchial grooves faint ( Fig. 1A, B View FIGURE 1 ). Front about 1/3 carapace width (FW/CW = 0.3); frontal margin straight ( Figs. 1A, B View FIGURE 1 , 2A View FIGURE 2 ); exorbital tooth small, blunt; epibranchial tooth reduced to granule; postfrontal crest sharply defined, complete, traversing entire carapace; lateral margin posterior to epibranchial tooth smooth ( Fig. 1A, B View FIGURE 1 ). Branchiostegite with two sutures, one longitudinal (epimeral), one vertical, dividing carapace sidewall into suborbital, subhepatic, pterygostomial regions, all smooth ( Fig. 2A View FIGURE 2 ).

Third maxillipeds filling entire oral field, except for transversely oval efferent respiratory openings at superior lateral corners; long flagellum on exopod of third maxilliped; ischium of third maxilliped with deep vertical sulcus ( Fig. 2D View FIGURE 2 ). Mandibular palp consisting of basis plus two articles; terminal article undivided, with small hardened ridge at junction between articles ( Fig. 2E View FIGURE 2 ). Anterior, posterior male thoracic sternum surface completely smooth; sternal sulci S1/2, S2/3 completely traversing sternum; S3/4 deep, U-shaped, completely traversing sternum; thoracic episternal sulci S4/E4, S5/E5, S6/E6, S7/E7 distinct ( Fig. 2B, C View FIGURE 2 ).

Dactylus of male right (major) chela distinctly arched, broad, with three well-spaced medium teeth interspersed by granule-like small teeth; immovable finger (propodus pollex) broad, cutting edge with three medium teeth proximally; both fingers touching at tip when chela closed, enclosing long oval interspace; palm of propodus of major chela enlarged, swollen, lower margin of distinctly concave ( Fig. 3A View FIGURE 3 ). Dactylus of male left (minor) chela long, slim, gently curved, with four well-spaced small teeth; immovable finger (propodus pollex) with four medium teeth interspersed by small teeth; both fingers touching at tips when chela closed, enclosing long oval interspace; minor chela propodus palm subequal to that of major chela, 0.8× propodus height of major chela; lower margin almost straight ( Fig. 3B View FIGURE 3 ). Cheliped merus elongated, almost as long as CW; cheliped merus inferior margins with four large well-separated teeth, distal meral tooth large ( Fig. 3C, D View FIGURE 3 ); cheliped carpus inner margin distal tooth medium sized, blunt; proximal tooth small, pointed, otherwise margin smooth ( Fig. 3E View FIGURE 3 ); ambulatory legs P2–5 stout, distal limb articles (merus, carpus, propodus, dactylus) not elongated; dactyli of P2–5 tapering to point, each bearing four rows of downward-pointing sharp bristles ( Fig. 1A View FIGURE 1 ). 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. 2B, C View FIGURE 2 ). G1TA about 1/3 G1SA length (G1TA/G1SA = 0.3), angled outward at 45° to longitudinal axis of G1SA; G1TA smooth, lacking setae except on central rounded crest, tapering sharply to pointed upcurved tip; G1TA widened basally; in three parts, ventral lobe low, dorsal lobe in two parts, high rounded crest medially, low lobe laterally, ventral lobe lined by long setae ( Figs. 4A–C View FIGURE 4 , 5B, C View FIGURE 5 ). G1SA widest at base, narrowest at G1TA-G1SA junction; basal G1SA mesial margin lined by long setae; G1SA lateral margin mostly smooth ( Figs. 4A View FIGURE 4 , 5B View FIGURE 5 ). G2SA ( Fig. 5A View FIGURE 5 ) long, slim, subequal to G1SA; G2SA widest at base, tapering sharply inward about one-third along length, last 2/3rds forming long, thin, tapering, upright process supporting long flagellum-like G2TA (G2TA/G2SA = 0.62) ( Fig. 5A View FIGURE 5 ). Medium-sized species, adult at CWs 34.0–39.0 mm.

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

Type locality. Yongoma River , 13 km south of Gonja, 579 m ASL, 1.6 km north of bridge at Pare (-4.354582°, 37.971104°) South Pare Mountains, Tanzania GoogleMaps .

Etymology. The species name, parekeeae , is derived from a combination of “pare” (a reference to the South Pare Mountains in northeastern Tanzania where the specimens were collected) and “kee”, from Dr Ngan Kee Ng, that is given a feminine ending. The specific epithet is used as a Latin noun in the genitive singular.

Distribution. Arcopotamonautes parekeeae n. sp. is known from three localities that are all in the South Pare Mountains in northeastern Tanzania ( Fig. 11 View FIGURE 11 ).

Habitat. This species is found in the Yongoma River in the forested highlands of the South Pare Mountains of northeastern Tanzania. The South and North Pare Mountains lie between Mount Kilimanjaro and the West Usambara Mountains, 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. The South Pare Mountains are separated from the West Usambara Mountains by the Mkomazi River valley. The South Pare Mountains support a range of montane habitats and a number of forest reserves, the largest of which is the Chome Nature Forest Reserve. Crabs were found in or near a shallow stream (1.5–1.8 m wide) flowing over a large rocky outcrop. The stream was heavily shaded by the dense vegetation growing above the outcrop. Crabs were either living on the stream bed between loose stones, or (more commonly) seen out of the water in stony areas near the stream banks.

Remarks. For comparisons see Remarks for A. ngae n. sp. below.