Potamonautes raybouldi, Cumberlidge & Vannini, 2004

Cumberlidge, Neil & Vannini, Marco, 2004, Ecology and taxonomy of a tree-living freshwater crab (Brachyura: Potamoidea: Potamonautidae) from Kenya and Tanzania, East Africa, Journal of Natural History 38 (6), pp. 681-693 : 683-689

Potamonautes raybouldi , new species

(figures 1, 2)

Type material. Tanzania:         (designated here): adult male (cw 55.7, cl 39.9, ch 20, fw 12.7 mm) ( NMU KMH 11486) from water-filled tree hole in forest 500 m asl, near Zigi , 9 km from Amani, East Usambara mountains , coll. J. N. Raybould, April 1966 ;          (designated here): two adult males (cw 40.5, cl 29.4, ch 14.2, fw 9.3; cw 39.6, cl 27.8, ch 13.2, fw 8.8 mm) ( NMU TRW 1966.03 . A.2), from water-filled tree holes in forest 500 m asl, near Zigi , 9 km from Amani, East Usambara mountains , coll. J. N. Raybould, April 1966 ; subadult female (cw 36.9, cl 26.4, ch 12.7, fw 9 mm), subadult male (cw 29.6, cl 21.6, ch 10.4, fw 7 mm) ( NMU TRW 1966.03 . B.2), from water-filled tree holes in forest 500 m asl, near Zigi , 9 km from Amani , East Usambara mountains, coll. J. N. Raybould, April 1966 ; adult male (cw 46.5, cl 33, ch 16.3, fw 11 mm), subadult female (cw 36.2, cl 25.8, ch 12.5, 8.6 mm) ( NMU TRW 1966.11 ), in water-filled tree holes in forest near Amani , East Usambara mountains, coll. J. N. Raybould, April 1966 .

Other material examined. Tanzania: subadult female (cw 39.5, cl 27.5, ch 13, fw 9.5 mm) ( NMU TRW 1988.05.18. A.1), from water-filled tree hole in forest near Zigi school, Amani area, East Usambara mountains , coll. J. N . Raybould, 18 May 1988; subadult female (cw 32.4, cl 22, ch 12.2, fw 8.5 mm), broken ( NMU TRW 1988.05.18. B.1), from water-filled tree hole in forest near Zigi school, Amani area, East Usambara mountains , coll. J. N . Raybould, 18 May 1988; subadult male (cw 30.5, cl 21.5, ch 10.5, fw 7.5 mm), subadult female (cw 34.5, cl 24.5, ch 12.5, fw 9 mm) ( NMU TRW 1988.05.18. C.2), from water-filled tree hole in forest near Zigi school, Amani area, East Usambara mountains , coll. J. N . Raybould, 18 May 1988; adult male (cw 48.6, cl 35.5, ch 17.7, fw 11.3 mm) ( NMU TRW 21.06.1989. A.1), hole in jackfruit tree, near police station, about 666 m asl, Kijijini, Amani , East Usambara mountains, coll. R. A . Kupe and S . Fedho, 21 June 1989; adult male (cw 46.9, cl 33.6, ch 16.9, fw 10.9 mm) ( NMU TRW 21.06.1989. B.1), hole in jackfruit tree, near police station, about 666 m asl, Kijijini, Amani , East Usambara mountains, coll. R. A . Kupe and S . Fedho, 21 June 1989; two subadult females (cw 36.5, cl 25.4, ch 12.1, fw 8.8 mm; cw 28, cl 20.5, ch 9, 8.4 mm), plus eight hatchlings ( NMU TRW 1970.07.10), Amani , East Usambara mountains, coll. J. N . Raybould; subadult male (cw 30.5, cl 25, ch 11.5, fw 9.5 mm) ( NMU TRW 1970.08 . A.1), Amani, East Usambara mountains , coll. J. N . Raybould; adult male (cw 51.5, cl 35.2, ch 18.5, fw 12 mm) ( NMU TRW 1970.08 . B.1), Amani, East Usambara mountains , coll. J. N . Raybould; adult male (cw 49.8, cl 36.1, ch 18.2, fw 12.8 mm) ( NMU KMH 11482), coll. 12 December 1971; adult female (cw 39.5, cl 29, ch 14.6, fw 9.8 mm) ( NMU KMH 11483), Amani, East Usambara mountains ; adult male (cw 46.6, cl 33, ch 16.7, fw 11.4 mm) ( NMU KMH 11487), Magoroto Hill , Muheza District , Tanga region (5°07∞ S, 38°45∞ E), coll. J . Bayliss (Frontier Tanzania); adult male (cw 41.8, cl 26.1, ch 14.9, fw 9.3 mm) ( NMU 1966.1 ), Amani , East Usambara mountains, coll. J. N . Raybould; 22 juveniles (cws 21.5– 8.5 mm) ( NMU KMH 11470–11495 ), Amani, East Usambara mountains; subadult female (cw 37.2, cl 25.4, ch 12.4, fw 9.4 mm) ( NMU 1988.1 ), Amani , East Usambara mountains, coll. J. N . Raybould; two subadult males (cw 37.1, cl 27.3, ch 12.8, fw 8.6 mm; cw 25, cl 19.2, ch 8.3, fw 6.2 mm), subadult female (cw 35.3, cl 26.4, ch 12.5, fw 8.4 mm) ( NMU 01 -02.1992.3), Tongwe Forest Reserve, Muheza District , Tanga (5°18∞ S, 38°44∞ E), coll. Frontier Tanzania, January to February, 1992; adult female (cw 41, cl 29.1, ch 14.2, fw 9.6 mm), with hatchlings, Amani, East Usambara mountains , coll. J. N . Raybould ( NMU TRW 07.2001.1) .

Kenya: subadult male (cw 25.6, cl 19.9, ch 9.4, fw 6.8 mm) ( NMU TRW 01.12.1984. A.1), Shimba Hills National Park, Kwala District, Coast Province , patch of forest, 330 m asl, coll. Patrick Muthama, 1 December 1984 ; subadult male (cw 35.5, cl 26.3, ch 13.2, fw 8.9 mm) ( NMU TRW 01.12.1984. B.1), Shimba Hills National Park, Kwala District, Coast Province , patch of forest, 330 m asl, coll. Patrick Muthama, 1 December 1984 ; adult female (cw 39.3, cl 28.4, ch 14, fw 9.3 mm) ( NMU TRW 01.12.1984. C.1), Shimba Hills National Park, Kwala District, Coast Province , patch of forest, 330 m asl, coll. Patrick Muthama, 1 December 1984 ; subadult male (cw 36.8, cl 27.7, ch 13.1, fw 8.7 mm) ( NMU TRW 12.10.1987.1), Shimba Hills National Park , coll. M. Boppré , 12 October 1987 ; subadult male (cw 14, cl 6.6, ch 6.9, fw 5.5 mm) ( NMU TRW 12.10.1987.1), Shimba Hills National Park , coll. M. Boppré , 12 October 1987 ; adult male (cw 48.1, cl 33.5, ch 16.6, fw 11.3 mm) ( NMU TRW 6.3.1988.1), Mangea Hill, Kilifi District (3°15∞ S, 39°43∞ E), 500 m asl, in tree hole, coll. A. Robertson and A. Luke , 6 March 1988 ; adult male (cw 53.1, cl 37, ch 19.7, fw 11.6 mm) ( USNM 1005070 ), Shimba Hills National Park (4°19.49∞ S, 39°31.47∞ E), from tree hole far from surface water, coll. V. Clausnitzer , 7 May 2000 ; juvenile and several hatchlings ( USNM 1005071 ), Muhaka Forest (4°19.49∞ S, 39°31.47∞ E), from tree hole, coll. R. Copeland , 13 April 2000 ; subadult male (cw 29.3 mm) ( NMK-DIZ 2002 /24), Muhaka Forest (4°19.49∞ S, 39°31.47∞ E), in tree hole, coll. R. Copeland , 12 May 2000 ; juvenile ( NMK-DIZ 2002 /25), Muhaka forest (4°19.49∞ S, 39°31.47∞ E), from tree hole, coll. V. Clausnitzer , May 2000; ( MZF 2608 ) , Gongoni forest, between Shimba Hills National Park and the sea, Kwala District, Coast Province , coll. Q. Luke, T. Luke and M. Vannini ; ( MZF 2609 ) , Gongoni forest, between Shimba Hills National Park and the sea, Kwala District, Coast Province , coll. Q. Luke, T. Luke and M. Vannini .

Diagnosis. Postfrontal crest sharp-edged, spanning entire carapace, lateral ends meeting anterolateral margins at epibranchial teeth. Exorbital tooth large, sharp, directed forward; epibranchial tooth small granule; anterolateral margin between exorbital, epibranchial teeth smooth, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth raised, granulated, end curving inward over carapace surface. Carapace highly arched, height greater than front width (ch/fw 1.5–1.7). Suborbital margin smooth, raised. Suborbital, subhepatic regions of carapace sidewall with fields of large granules, pterygostomial region smooth. Third thoracic sternal sulcus s3/s4 complete, deep, V-shaped, not meeting anterior margin of sterno-abdominal cavity. Thoracic episternal sulci s4/e4, s5/e5, s6/e6 and s7/e7 all complete. Second carpal tooth of carpus of cheliped pointed, large, half size of first tooth, directed at 70–90° angle to first tooth. Tip of terminal article of gonopod 1 curving sharply upward; terminal article distinctly widened in middle by high medial fold. Inner and outer surfaces of merus, carpus, and of palm of propodus of cheliped all with conspicuous reticulated rust-red pattern over cream background.

Description. Carapace ovoid, wide (cw/fw 4.3–4.5), highly arched (ch/fw 1.5–1.7), semi-circular, urogastric grooves, deep; cervical grooves short, faint; dorsal surface of carapace smooth, lacking carinae, striae or granules. Front slightly indented, anterior margin folded sharply downward, relatively narrow, less than one-quarter carapace width (fw/cw 0.22–0.23). Postfrontal crest sharp-edged, granular, spanning entire carapace, epigastric crests continuous with postorbital crests, lateral ends of postfrontal crest meeting anterolateral margins at epibranchial teeth. Exorbital tooth large, sharp, directed forward; epibranchial tooth small granule; anterolateral margin between exorbital and epibranchial teeth smooth, lacking intermediate tooth; anterolateral margin posterior to epibranchial tooth raised, granular, end curving inward over carapace surface. Suborbital margin smooth, raised. Posterior margin of carapace narrow, only slightly wider than frontal margin (pmw/fw 1.1).

Carapace sidewall divided into three parts by longitudinal (epimeral), and vertical (pleural) grooves. Longitudinal groove granular, medial part defined by two rows of granules, beginning medially at lower margin of orbit, curving backward across sidewall, dividing suborbital, subhepatic regions from pterygostomial region. Vertical groove short, granular, meeting anterolateral margin midway between exorbital and epibranchial teeth, dividing suborbital from subhepatic region. Suborbital, subhepatic regions of carapace sidewall with fields of large granules, pterygostomial region smooth, except in region of medial part of longitudinal groove. First thoracic sternal sulcus s1/s2 faint; second sulcus s2/s3 deep, running horizontally across sternum; third sulcus s3/s4 complete, deep, V-shaped, deep at edges, shallow in middle, not meeting anterior margin of sterno-abdominal cavity; sternal sulci s4/s5 and s5/s6 incomplete in the midline of the sterno-abdominal cavity; thoracic episternal sulci s4/e4, s5/e5, s6/e6 and s7/e7 all complete. Third maxillipeds filling entire oral field, except for transversely oval respiratory openings at superior lateral corners; long flagellum on exopod of third maxilliped; ischium of third maxilliped with deep vertical sulcus. Epistomial median tooth well developed, triangular, with granulated margin. Mandibular palp two-segmented; terminal segment single, undivided, with setae but no hard flap at junction between segments. Abdomen slim triangle, sides straight, tapering inward; segments a1–a6 of male abdomen each four-sided, a3 widest, a6 longest; telson broad triangle with rounded apex.

Chelipeds unequal, left much longer and higher than right; outer, inner surfaces of palm of propodus of cheliped swollen, mottled, with clear red-brown reticular pattern over cream background; outer, inner surfaces of dactylus and of pollex of propodus of cheliped pitted, curved; fingers of major cheliped with four large rounded teeth; fingers enclosing long narrow interspace when closed, tips overlapping. First carpal tooth of inner margin of carpus of cheliped large, pointed; second carpal tooth pointed, set at 70° angle to first carpal tooth, half size of first tooth. Anterior and posterior inferior margins of merus of cheliped lined by small rounded teeth, large pointed tooth at distal end of inferior surface; superior surface of merus roughened with carinae, with same red-brown reticular pattern seen on palm of propodus; meral tympanum present. Pereiopods p2–p5 slender, elongated, p3 longest, p5 shortest; dactyli of p2–p5 tapering, pointed, each bearing four rows of downward-pointing sharp spines.

Terminal article of gonopod 1 relatively short (ratio of length of terminal article to subterminal segment 0.35), directed outward at 45° angle to vertical; tip curving sharply upward; longitudinal groove on terminal article broad along entire length, clearly visible on ventral, superior sides; not visible on dorsal side; medial fold of ventral side of terminal article higher than lateral fold so that middle of article distinctly widened; junction between terminal article and subterminal segment of gonopod 1 marked by deep sulcus ventrally and dorsally; broad dorsal membrane at junction. Subterminal segment of gonopod 1 broad at base, tapering distally, long setae along both margins and along margin of longitudinal flap. Gonopod 2 longer than gonopod 1, terminal article of gonopod 2 flagellum-like, shorter than subterminal segment.

Size. Adult size range of males and females beginning at around cw 39 mm.

Colour. Upper surface of carapace dark grey/brown, ventral thoracic surface dull white, postfrontal crest cream; both sides of merus, carpus, propodus of cheliped (p1) with conspicuous characteristic reticulated rust-red pattern over cream background; distal half of merus of cheliped orange, basal half dark grey; all other joints of chelipeds orange; few dark chromatophores on dorsal surfaces; orange pigment granular; basal segments of walking legs dark grey, with dense dark chromatophores; propodi, dactyli of p2–p5 tinged with orange, but not as vividly coloured as chelipeds (p1).

Distribution. The highland regions of coastal East Africa, in south-east Kenya and north-east Tanzania. The species is known from upland localities in coastal Kenya (the Shimba Hills and the Mangea Hills in the Kwala and Kilifi Districts). Potamonautes raybouldi has been found in tree holes in the lowland coastal forests of Kenya in the Buda Forest (4°27∞79S, 39°24∞20E, 88 m asl) and in the Makadara Forest, but has not been recorded from the lowland forest at either Arabuko-Sokoke (3°18∞01S, 39°59∞14E, 30 m asl), or the Mrima Hills (4°29∞32S, 39°15∞27E, 146 m asl). In Tanzania, P. raybouldi is known from the highland regions of the East Usambara mountains in the north-east part of the country. We are aware of unconfirmed reports of the presence of P. raybouldi in the South Pare mountains, Mt Tongwe, and the West Usambara mountains in Tanzania.

Type locality. Zigi , 9 km from Amani , East Usambara mountains, Tanzania, East Africa .

Comparisons. The new species is assigned to Potamonautes because it possesses the following combination of characters: the anterolateral margin lacks an intermediate tooth between the exorbital and epibranchial teeth; the mandibular palp is two-segmented; and the third maxilliped exopod has a long flagellum, reaching beyond the upper margin of the merus of the third maxilliped (Cumberlidge, 1997, 1998, 1999). Although Bott (1955) recognized 15 subgenera of Potamonautes , we prefer here to follow Cumberlidge (1999) and use Potamonautes sensu lato for all species, pending a revision of the entire genus (Cumberlidge, in preparation).

Potamonautes raybouldi is compared here to P. loveridgei (Rathbun, 1933) , P. lirrangensis (Rathbun, 1904) , P. johnstoni (Miers, 1885) , P. suprasulcatus (Hilgendorf, 1898) and P. infravallatus (Hilgendorf, 1898) . These East African species are similar to P. raybouldi in that they have a prominent and complete postfrontal crest, a predominantly smooth carapace texture, a small granular epibranchial tooth, and a complete V-shaped thoracic sternal groove s3/s4. However, there are a number of characters that distinguish P. raybouldi from the species listed above.

Potamonautes raybouldi is closest to P. loveridgei from the eastern part of the Democratic Republic of Congo (formerly Zaire) and western Tanzania (Rathbun, 1933; Bott, 1955). This species was described and illustrated by Rathbun (1933: 251–253, pls 1, 2, figure 3) as Potamon (Potamonautes) loveridgei , by Balss (1936) as Potamon (Potamonautes) johnstoni stappersi Balss, 1936 , and by Bott (1955: 263, figure 31, pl. 14, figure 1a–d) as P. (Tripotamonautes) loveridgei . However, there are a number of characters that distinguish P. loveridgei from the specimens from Kenya and Tanzania under consideration here. For example, the carapace of P. raybouldi is not as high as that of P. loveridgei (ch/fw P. raybouldi 1.5, P. loveridgei 1.7); the pterygostomial region of the carapace sidewall of P. raybouldi is smooth (whereas this region is distinctly granular in P. loveridgei ); the second carpal tooth of the carpus of the cheliped of P. raybouldi is set at a wide angle (70– 90°) to the first carpal tooth (whereas in P. loveridgei this angle is more acute); and the tip of the terminal article of gonopod 1 of P. raybouldi is strongly upcurved (whereas that of P. loveridgei is only weakly upcurved).

Potamonautes lirrangensis from the Democratic Republic of Congo, Tanzania and Malawi (Bott, 1955) is a common and relatively well-known species that has been described and illustrated by Rathbun (1904: pl. 14, figure 8; Rathbun, 1905: 169) as Potamon (Potamonautes) lirrangensis ; by Chace (1942: 188, figures 1, 2) and Capart (1954: 836, figure 28) as Potamon lirrangensis ; and by Bott (1955: 268–270, figures 38, 39, 83, pl. 16, figure 2a–d) as Potamonautes (Lirrangopotamonautes) lirrangensis lirrangensis . Potamonautes raybouldi can be distinguished from P. lirrangensis as follows. The carapace of P. raybouldi is higher than that of P. lirrangensis (ch/fw P. raybouldi 1.5, P. lirrangensis 1.2); the epibranchial tooth of P. lirrangensis is small and pointed (whereas that of P. raybouldi is a small rounded granule); and the anterolateral margin of P. lirrangensis behind the epibranchial tooth has several short pointed spines (whereas this margin is granular in P. raybouldi ).

Potamonautes johnstoni Miers, 1885 from Tanzania was described and illustrated by Bott (1955: 265–266, figure 36a, b, pl. XV, figure 2a–d) as Potamonautes (Lirrangopotamonautes) johnstoni johnstoni . Potamonautes raybouldi can be distinguished from P. johnstoni as follows. The carapace of P. raybouldi is higher than that of P. johnstoni (ch/fw P. raybouldi 1.5, P. johnstoni 1.1); the frontal margin of P. raybouldi is narrower than that of P. johnstoni (fw/cw P. raybouldi 0.26, P. johnstoni 0.29); the exorbital tooth of P. johnstoni is low and smooth (whereas this tooth is sharply pointed in P. raybouldi ); and the suborbital and subhepatic regions of the carapace sidewall of P. johnstoni are completely smooth (whereas these regions of the sidewall are heavily granular in P. raybouldi ).

Williams et al. (1964) reported the occurrence of P. suprasulcatus (Hilgendorf, 1898) and P. infravallatus (Hilgendorf, 1898) from Mount Kilimanjaro, Arusha and the Usambara mountains in north-east Tanzania. Potamonautes suprasulcatus was described and illustrated by Bott (1955: 270–272, 235, figure 40, pl. 17, figure 1a–d) as Potamonautes (Arcopotamonautes) suprasulcatus suprasulcatus while P. infravallatus was described and illustrated by Bott (1955: 270–272, 235, figure 40, pl. 17, figure 1a–d) as Potamonautes (Rotundopotamonautes) infravallatus . Potamonautes raybouldi can be distinguished from these two species as follows. The carapace of P. raybouldi is distinctly higher than that of P. suprasulcatus (ch/fw P. raybouldi 1.5, P. suprasulcatus 1.2); the cervical groove in P. suprasulcatus is very long and deep (whereas that of P. raybouldi is short and shallow); the suborbital and subhepatic regions of the carapace sidewall of P. suprasulcatus are completely smooth (whereas these regions of the sidewall are heavily granular in P. raybouldi ); and the terminal article of gonopod 1 of P. suprasulcatus is long, slim, curved, tapering and needle-like (whereas that of P. raybouldi is distinctly widened by a high crest in the middle of the terminal article). Potamonautes infravallatus is a much smaller species than P. raybouldi (i.e. crabs are adult at cws 28 and 39 mm, respectively), and P. infravallatus has a very short, cone-shaped terminal article on gonopod 1 with tufts of setae (rather than a smooth terminal article which is angled, widened in the middle, and with a distinctly upturned tip).

Remarks. The phenomenon of phytotelmy—inhabiting small pools of water within or upon plants—was first reported in true freshwater crabs from Africa by Cumberlidge (1991, 1996a, 1996b, 1999) and Cumberlidge and Sachs (1991, 2000), who described this unusual habit in Globonautes macropus Rathbun, 1898 (Globonautinae) which lives in water-filled tree holes in the rainforests of Liberia, West Africa. The present work is the first record of the occurrence of a phytotelmic true freshwater crab in East Africa. The only other records of true freshwater crabs inhabiting water-filled holes in trees that we are aware of are those by Ng (1991) for Archipelothelphusa (Parathelphusidae) from the Philippines, Ng (1995) for Ceylonthelphusa scansor Ng, 1995 (Parathelphusidae) from Sri Lanka, and by Cumberlidge et al. (2002b) for Malagasya goodmani (Cumberlidge, Boyko and Harvey, 2002) (Potamonautidae) from Madagascar. The latter species lives in the temporary water-filled pools that collect in the leaf axils of Pandanus palms. Clearly, true freshwater crabs that live in water-filled holes in trees are extremely rare, especially when the fact that there are more than 900 species of true freshwater crabs worldwide is taken into consideration (Cumberlidge, unpublished).

Although rare in true freshwater crabs, several groups of tropical crabs use trees to different degrees. Many tree-living crabs that lay their eggs directly into the sea (e.g. Aratus , mangrove sesarmids and mangrove grapsids) appear to climb trees for protection, concealment and a source of fresh leaves to eat, rather than as a source of a freshwater microhabitat (Vannini and Ruwa, 1994; Vannini et al., 1997). Other tree-living crabs, such as the grapsid Metopaulias from tropical America (von Hagen, 1977; Diesel, 1989; Abele, 1992), and some species of Geosesarma from South-East Asia (Ng, 1988, 1995), appear to be phytotelmic (like P. raybouldi ), relying on sources of freshwater in trees (rather than seawater) to complete their life cycle.