Hydrothelphusa madagascariensis (A. Milne-Edwards, 1872)

Cumberlidge, N., Reed, S. K. & Boyko, C. B., 2004, Distribution patterns of the Malagasy freshwater crabs (Crustacea: Decapoda: Brachyura), Journal of Natural History 38, pp. 1133-1157 : 1141-1146

Hydrothelphusa madagascariensis (A. Milne-Edwards, 1872)

(figure 2B)

Thelphusa madagascariensis A. Milne-Edwards, 1872: 1 (type locality: Sakaleone River , near Bombetok, Madagascar).

Potamon (Potamon) madagascariensis Rathbun, 1904: 264 , figure 7, pl. 9, figure 9; Balss, 1929: 254.

Potamon (Potamon) humbloti Rathbun, 1904: 211–219 , pl. 12, figure 10 (type locality: Madagascar).

Potamon (Potamon) grandidieri Rathbun, 1904: 298 , figure 29, pl. 12, figure 11; Balss, 1929: 354 (type locality: Madagascar).

Potamon (Potamon) bombetokensis Rathbun, 1904: 298–299 , pl. 12, figure 6; Balss, 1929: 354 (type locality: Bombetok , Madagascar).

Bottia madagascariensis Pretzmann, 1961: 163 , figure 2.

Bottia madagascariensis reticulata Pretzmann, 1961: 163 , figure 2 (type locality: Androkabe-Bach , near Fort Dauphin (= Tolagnaro), Madagascar).

Bottia bombetokensis Pretzmann, 1961: 164 , figure 4.

Hydrothelphusaagilis madagascariensis Bott, 1965: 341–342 , pl. 3, figures 10, 11; Rabeharisoa, 1996: 156–157.

Hydrothelphusa humbloti Bott, 1965: 342–344 , not pl. 3, figures 12, 13, not figures 5, 6; Cumberlidge, 1997: 585.

Hydrothelphusa madagascariensis Cumberlidge, 1997: 585 ; 1998: 209; Cumberlidge and Boyko, 2001: 126–127; Cumberlidge and Sternberg, 2002: 51–54, figures 1B, 3B, 4B, 5B, 6B, 7C, D, 8B, 9E–I, 11B).

Hydrothelphusa bombetokensis Cumberlidge and Sternberg, 2002: 54–56 , figures 1C, 3C, 4C, 5C, 6C, 7E, F, 8C, 9N–Q, 11C, tables 1 –4.

Material examined. All coll. J.-M. Elouard and colleagues (see Acknowledgements). Madagascar: one juvenile male (cw 22.5 mm), Antananarivo Province, Réserve Spéciale d’Ambohitantely, jardin botanique, 24 km north-east of Ankazobe , 1450 m, 18°10∞1∞∞S, 47°16∞6∞∞E, 15 December 1997 ( FMNH 5472 ) . One juvenile female (cw 19.7 mm) affluent of Ihazofotsy River, basin of Onilahy River , near Inabinda, 11 April 1992 ( FMNH 5712 ) . One female (cw 50.1 mm), one male (cw 44 mm), together with H. goudoti ( FMNH 5720 ) . One juvenile ( FMNH 5722 ) . One juvenile male (cw 24.3 mm), basin of Rianila River, Sahatiravona River, 25 m asl, 18°57∞11∞∞S, 48°51∞06∞∞E, Ranomafana , 22 December 1990 ( FMNH 5723 ) . Two juvenile males (cws 25.5, 27.8 mm), two juvenile females (cws 23.3, 23.4 mm), affluent of Namorona River, basin of Namorona River , Ranomafana, 820 m asl, 21°14∞57∞∞S, 47°25∞32∞∞E, 14 November 1993 ( FMNH 5727 ) . One juvenile female (cw 18.3), three males (cws 46.9, 50.6, 56.1 mm), Lantara River, basin of Manampatrana River , Andringitra, 1370 m asl, together with H. agilis , 22°13∞23∞∞S, 47°01∞53∞∞E, 16 November 1993 ( FMNH 5728 ) . Four males (cws 17.1, 23.5, 25.2, 31.2 mm), five females (cws 18.3, 27.1, 28, 28.8, 32.1 mm), Sahavatov River, basin of Manampatrana River , Andringitra camp II, 1390 m asl, 22°13∞33∞∞S, 47°00∞50∞∞E, 20 November 1993 ( FMNH 5730 ) . Two males (cws 23.8, 29.7 mm), one female (cw 32.9 mm) ( FMNH 5731 ) . One subadult female (cw 24.2 mm), together with H. agilis, Ambatandrano River, Ambatandrano, 21°14∞45∞∞S, 47°26∞32∞∞E, 17 April 1994 ( FMNH 5735 ) . Five males (cws 13.6, 15, 17.6, 18.3, 19.1 mm), Namorona River, basin of Namorona River , lfanadiana-Tolongoina road, 500 m asl, 21°22∞40∞∞S, 47°35∞55∞∞E, 22 April 1994 ( FMNH 5737 ) . One female (cw 38 mm), basin of Efaho River , Ranopiso Iambany, 45 m asl, 25°02∞13∞∞S, 46°40∞23∞∞E, 15 May 1994 ( FMNH 5745 ) . One male (cw 33.9 mm), Sahambano River, basin of Mananara-sud River , 570 m asl, 22°29∞21∞∞S, 46°17∞37∞∞E, 25 May 1995 ( FMNH 5748 ) . One female (cw 43.2 mm), Manampatrana River, basin of Manampatrana River, Mahazoalala village , 170 m asl, 22°40∞55∞∞S, 47°17∞49∞∞E, 18 June 1995 ( FMNH 5749 ) . Two males (cws 20.4, 22.9 mm), one female (cw 25.8 mm), Mazy River, affluent of the Sakay River , basin of Tsiribihina River , Réserve Naturelle Intégrale d’Amparaky, 975 m asl, 18°56∞03∞∞S, 46°38∞07∞∞E, 11 October 1995 ( FMNH 5752 ) . One male (cw 18.9 mm), Lily River, affluent of Mahajilo River, basin of Tsiribihina River , Antafofo, 1100 m asl, 19°01∞43∞∞S, 46°41∞07∞∞E, 8 October 1995 ( FMNH 5753 ) . One male, Ambatomisana River, basin of Betsiboka River , Geranium-usine, 18°27∞03∞∞S, 47°56∞47∞∞E, 18 October 1995 ( FMNH 5754 ) . One male (cw 44.5 mm), one female (cw 41.7 mm), Vanjainanitra River, basin of Betsiboka River , Amboasary, 1300 m asl, 18°26∞03∞∞S, 47°56∞40∞∞E, 25 October 1995 ( FMNH 5755 ) . One juvenile male (cw 17.5 mm), Ambahibe River, basin of Efaho River , Isaka-Ivondro, 70 m asl, 24°46∞47∞∞S, 46°51∞53∞∞E, 20 November 1995 ( FMNH 5758 ) . Seven subadult males (cws 20.8, 25.2, 28.2, 28.6, 32.3, 32.8, 34.8 mm), four subadult females (cws 27.5, 28.2, 29.6, 32.8 mm) Betoreo River, basin of Efaho River , 115 m asl, 24°47∞20∞∞S, 46°53∞48∞∞E, 24 November 1995 ( FMNH) . One juvenile male (cw 23.7 mm), two juvenile females (cws 21.4, 23.8 mm), affluent of Andranohela River, basin of Manampanihy River , camp I Andohahela, 575 m asl, 24°36∞37∞∞S, 46°45∞31∞∞E, 24 November 1995 ( FMNH 5759 ) . Two subadult females (cws 25.7, 33.2 mm), Sakamalio River, basin of Mandrare River , Andohahela, 480 m asl, 24°31∞03∞∞S, 46°38∞32∞∞E, 2 February 1996 ( FMNH 5762 ) . One male (cw 37.6 mm), Sahaomby River, basin of Tsiribihina River , Manatoloza, 1800 m asl, 19°25∞50∞∞S, 46°57∞53∞∞E, 21 May 1996 ( FMNH 5763 ) . One juvenile male (cw 20.8 mm), Vanjainanitra River, basin of Betsiboka River , Amboasary, 1300 m asl, 18°26∞03∞∞S, 47°56∞40∞∞E, 31 October 1996 ( FMNH 5764 ) . One juvenile male (cw 24.8 mm), Sahaomby River, basin of Tsiribihina River , Manatoloza, 1800 m asl, 19°02∞50∞∞S, 46°57∞53∞∞E, 14 November 1996 ( FMNH 5769 ) . One juvenile male (cw 19.8 mm), Mananara River, basin of Betsiboka River , Anjozorobe, 18°24∞47∞∞S, 47°52∞53∞∞E, 1220 m asl, 16 November 1996 ( FMNH 5771 ) . Three males (cws 13, 13.3, 26.2 mm), Mananta River, basin of Namorona River , Mananta, 18°19∞17∞∞S, 47°56∞27∞∞E, 19 November 1996 ( FMNH 5772 ) . Two juveniles, Makis River, basin of Antongombato River , base camp, 1030 m asl, 19 March 1999, 12°31∞27∞∞S, 49°10∞21∞∞E ( FMNH 5804 ) . Two males (cws 11.2, 11.3 mm) Makis River, basin of Antongombato River , 1050 m asl, 49°10∞21∞∞E ( FMNH 5805 ) .

All coll. S. M. Goodman. Fifteen specimens, Fianarantsoa Province, camp I, exterior of northern limit of Réserve Spéciale du Pic d’Ivohibe, 7 km east-north-east of Ivohibe, 22°28∞2∞∞S, 46°57∞6∞∞E, 900 m asl, along Ilefitany River, 1997 ( FMNH 5464 ) . Five adult females (cws 52.5, 53.1, 53.4, 54.2, 59.4 mm), two subadult females (cws 45.3, 49 mm), one adult male (cw 61.9 mm), one subadult male (cw 41.5 mm), two juvenile males (cws 25.7, 31 mm), Antananarivo Province, Réserve Spéciale d’Ambohitantely , 24 km NE Ankazobe, 1450 m, 18°10.1∞S, 47°16.6∞E, 15 December 1997 ( FMNH 5471 ) . One juvenile ( FMNH 5802 ) . One male (cw 10.4 mm) ( FMNH 5808 ) . One male (cw 43.6 mm), peach fur on dorsal carapace, Marojejy , camp I, 600 m asl, 14°26∞S, 49°44∞E ( FMNH 6632 ) . Three males (cws 38.6, 48.4, 49.9 mm), east of Anjanaharibe, 1600 m asl, western slopes of the massif d’Anjanaharibe-Sud (Antsiranana Province), site 1, 13.5 km south-west of Befingotra , 14°47∞0∞∞S, 49°26∞5∞∞E, 1200 m asl, along Analabe River, 25 October to 2 November 1999 ( FMNH 6633 ) . One male (cw 49.8 mm), one female (cw 47.7 mm), Marojejy , camp III, 800 m asl ( FMNH 6634 ) . One male (cw 48.6 mm), peach fur on carapace, east of Anjanaharibe, western slopes of the massif d’Anjanaharibe-Sud (Antsiranana Province), camp site I, 800 m asl, 13.5 km south-west of Befingotra, 14°47∞0∞∞S, 49°26∞5∞∞E, 1200 m asl, along Analabe River, 25 October to 2 November 1999 ( FMNH 6636 ) . Four males (cws 39.8, 48.8, 53.8, 56.8 mm) east of Anjanaharibe (Antsiranana Province), 1200 m asl ( FMNH 6637 ) . One male (cw 33.3 mm), Marojejy , camp III, 1200 m asl, 14°26∞S, 49°44∞E ( FMNH 6638 ) . One male (cw 45.2 mm), Betaolana forest, 800 m asl, site 1, 8.5 km north-west of Ambodiangezoka, along Ambolokopatrika River (Antsiranana Province), 820 m asl, 14°32∞3∞∞S, 49°26∞3∞∞E, 7–14 October 1999 ( FMNH 6639 ) .

Distribution. Hydrothelphusa madagascariensis is the commonest and most widely distributed species of freshwater crab in Madagascar. It is found in the streams and rivers of the central highlands in all six provinces, from Tolagnaro in the south to Antsiranana in the north (figure 2B). Figure 2B includes a total of 53 different localities for H. madagascariensis from the present study and from the literature (Rabeharisoa, 1996; Cumberlidge, 1997, 1998; Cumberlidge and Boyko, 2001; Cumberlidge and Sternberg, 2002). Hydrothelphusa madagascariensis is sympatric with H. agilis ( FMNH 5728, 5735) and with H. goudoti ( FMNH 5720). Hydrothelphusa madagascariensis is found mainly in the headwaters of 10 major river basins in five Malagasy provinces in latitudes between 12° and 25°S. These are the basins of the Antongombato (Antsiranana Province), Betsiboka and Tsiribihina (Antananarivo Province), Namorona, Manampatrana and Mananara-Sud (Fianarantsoa Province), Rianila (Toamasina Province), and the Efaho, Mandrare and Manampanihy (Toliara Province) Rivers. Hydrothelphusa madagascariensis has been collected from a range of elevations from 25 m asl (in a stream in the basin of the Rianila River) to 1390 m asl in the Andringitra massif. The southern localities in Toliara Province are close to the limits of the humid forest biome, and crabs are absent from the xerophytic zone which begins to the west of the Anosyennes Mountains. The headwaters of the Mandrare River in Toliara Province flow through humid forest, but the lower section of the river passes through arid spiny bush country, its river bed is seasonally dry, and crabs are therefore absent.

Conservation status. Hydrothelphusa madagascariensis is a widespread and abundant species. It has been collected recently, and its conservation status is secure ( table 1). This species is found in three protected areas in Antsiranana Province (the Réserve Spéciale de l’Anjanaharibe-Sud, the Réserve Spéciale de l’Ankarana and the Parc National de Marojejy ). It is also found in two protected areas in Antananarivo Province (the Réserve naturelle Intégrale d’Amparaky and the Réserve Spéciale d’Ambohitantely) and three in Fianarantsoa Province (the Parc National de Ranomafana , the Parc National d’Andringitra and the Réserve Spéciale du Pic d’Ivohibe) .

Remarks. Hydrothelphusa madagascariensis was redescribed by Cumberlidge and Sternberg (2002) from the largest male paralectotype, a subadult ( MNHN-B 4352) from the Sakaleone River near Bombetok in the central highland region (20°34∞S, 47°49∞E). This specimen has distinct fields of granulations in the anterolateral regions of the dorsal carapace, and on the suborbital and pterygostomial regions of the carapace sidewall, and has a row of large raised granules on both inferior margins of the merus of pereiopod 1. The major dactylus of the cheliped of this subadult specimen is not strongly arched and the dentition on the propodus is small and unremarkable. Potamon (Potamon) bombetokensis was described by Rathbun (1904) from an adult male, cw 50.1 mm ( MNHN-B 6396), from Bombetok in the central highland region of Madagascar. This specimen has faint granulations in the anterolateral regions of the dorsal carapace, and on the suborbital and pterygostomial regions of the carapace sidewall, and one inferior margin of the merus of pereiopod 1 has small granules, while the other margin is smooth. The major dactylus of the cheliped of this specimen is strongly arched and the dentition on the propodus has a large proximal molariform cluster. All of these characters were found here to vary with age (see below), and it is clear that H. madagascariensis exhibits a great deal of intraspecific variation. The moults that occur in adult males of H. madagascariensis (cw 50 mm and above) bring about a transformation of the carapace and cheliped characters that are different enough to have prompted some authors to describe different life stages of this taxon as different species. For example, Rathbun (1904) described Potamon (Potamon) humbloti Rathbun, 1904 from a subadult male specimen that was later re-identified and synonymized with H. madagascariensis (Cumberlidge and Sternberg, 2002) .

We consider it likely, based on the present work, that A. Milne-Edwards’ (1872) original description of Thelphusa madagascariensis was based on a subadult specimen, whereas Rathbun’s (1904) description of Potamon (Potamon) bombetokensis from an adult male specimen (cw 50.1 mm), and Cumberlidge and Sternberg’s (2002) description of H. bombetokensis from even larger specimens (cws 50–61 mm), were each using adult specimens of H. madagascariensis .

The large series of specimens of H. madagascariensis available for the present study made it possible to describe intraspecific variation shown by characters of the carapace and chelipeds that have previously been considered to be diagnostic for the species. Examination of a series of specimens of different sizes (ages) that included juveniles (cw <30 mm), subadults (cws 30–49 mm) and adults (cws 50 mm or greater) from the same geographical locality ( FMNH 5464 and 5471) revealed the following variation in characters: (1) the anterolateral regions of the dorsal carapace of adults are smooth and arched, whereas these regions in juveniles and subadults are granulated and flattened; (2) the suborbital and pterygostomial regions of the carapace sidewall of adults are distinctly granulated, whereas these regions in juveniles and subadults are either smooth, or only faintly granulated; (3) the inferior margins of the merus of pereiopod 1 of adults are distinctly granulated, whereas these margins in juveniles and subadults are either only weakly granulated, or completely smooth; and (4) the cheliped of adult males has undergone a dramatic transformation: the dactylus is distinctly curved to form an arch that encloses a permanent gape, and the propodus has developed a characteristic large proximal molariform cluster with three or four fused teeth. The cheliped of subadult males (30–49 mm) and juveniles (cw <29 mm) lacks the curved dactylus and the proximal molariform cluster on the propodus is unformed and inconspicuous.

Specimens of similar size from different geographical localities in the north-east ( FMNH 6637), central ( FMNH 5772) and south-east ( FMNH 5762) parts of the island did show variation in the colour of their carapace and legs, but did not show a great deal of variation in carapace or gonopod characters. Specimens of H. madagascariensis from Marojejy in Antsiranana Province ( FMNH 6633, 6636) and from Ilefitany in the Réserve Spéciale du Pic d’Ivohibe in Fianarantsoa Province ( FMNH 5464) have a distinct covering of short peach fur on their dorsal carapace. The subadult female ( FMNH 5749) from the river Manampatrana in Fianarantsoa Province has several character states (carapace outline and pointed exorbital and epibranchial teeth) that are similar to those of H. agilis . However, characters of the suborbital margin, carapace sidewalls, and merus and carpus of pereiopod 1 of this specimen indicate that it belongs to H. madagascariensis .

Comparisons. Hydrothelphusa madagascariensis can be distinguished from H. agilis and H. goudoti as follows. The frontal margin of the carapace of H. madagascariensis is neither horizontal (as in H. agilis ) nor strongly deflexed (as in H. goudoti ); in addition, the suborbital margin of H. madagascariensis is granulated but it is neither strongly toothed (as in H. agilis ) nor smooth (as in H. goudoti ); the subhepatic and pterygostomial regions of the carapace sidewall of H. madagascariensis are granulated but not smooth (as in H. agilis and H. goudoti ), and the fingers of the right and left propodi of the chelipeds of adult males of H. madagascariensis has a characteristic large molariform cluster of three or four fused teeth which are not seen in H. agilis and H. goudoti .

Hydrothelphusa madagascariensis can be further distinguished from H. goudoti by the following characters. The carapace of H. madagascariensis is less wide (cw/fw 3.4) and less arched (ch/fw 1.3) than that of H. goudoti (cw/fw 3.9, ch/fw 1.6); the exorbital angle tooth and the epibranchial tooth of H. madagascariensis are both large and triangular, whereas these teeth in H. goudoti are small and blunt; the suborbital and pterygostomial regions of the carapace sidewall of H. madagascariensis are both heavily granulated, whereas those of H. goudoti are smooth; and the cervical grooves of H. madagascariensis are very short, whereas those of H. goudoti are very long.

Differences in the carapace proportions between H. madagascariensis and H. bombetokensis (carapace width, cw/fw 3.4 versus 3.5, and carapace height, ch/fw 1.2 versus 1.3) reported by Cumberlidge and Sternberg (2002) are probably not significant in the light of the findings of the present study. Similarly, differences in carapace texture (either granular with carinae, or smooth) used to distinguish between H. madagascariensis and H. bombetokensis are also not supported in the present study, and could be accounted for by intraspecific variability in these characters. Finally, no significant differences could be found between the form of the terminal article of gonopod 1 in H. madagascariensis and in specimens formerly assigned to H. bombetokensis . This knowledge of character variability has been derived from the examination of a large series of specimens of different ages, and makes the boundaries between H. madagascariensis and H. bombetokensis very unclear. For these reasons we do not recognize H. bombetokensis here as a distinct taxon.