Hydrothelphusa

Key to the species of Hydrothelphusa 1 Inferior margins of merus of pereiopod 1 with either large teeth or large granules; anterior carapace texture distinctly granular with short carinae................................................................................................... 2 - Inferior margins of merus of pereiopod 1 either smooth or faintly granular; anterior carapace texture completely smooth.............................................................................................................................................. 4 2 Frontal margin clearly toothed; front horizontal (not deflexed); suborbital margin with large pointed teeth; suborbital region of carapace sidewall smooth (Cumberlidge & Sternberg 2002: Fig. 1 A).................................................................................................................................................................................. H. agilis - Frontal margin granular; front moderately deflexed; suborbital margin granular; suborbital region of carapace sidewall granular................................................................................................................................. 3 3 Subhepatic regions of carapace sidewall heavily granulated..................................... H. madagascariensis - Subhepatic region of carapace sidewall smooth........................................................................ H. vencesi 4 Exorbital, epibranchial teeth both slim, long, pointed; distinct gap between epigastric, postorbital crests (Cumberlidge & Sternberg 2002: Fig. 1 C).................................................................... H. bombetokensis - Exorbital, epibranchial teeth both low, blunt; epigastric, postorbital crests fused forming horizontal postfrontal crest (Cumberlidge & Sternberg 2002: Fig. 1 D)............................................................ H. goudotiPublished as part of Cumberlidge, Neil, Marijnissen, Saskia A. E. & Thompson, Jonelle, 2007, Hydrothelphusa vencesi, a new species of freshwater crab (Brachyura: Potamoidea: Potamonautidae) from southeastern Madagascar., pp. 61-68 in Zootaxa 1524 on page 67, DOI: 10.5281/zenodo.17749

Hydrothelphusa vencesi Cumberlidge, Marijnissen & Thompson, 2007, n. sp.

Hydrothelphusa vencesi n. sp. (Figs. 1–17) Type material examined: MADAGASCAR: adult male, holotype (designated here, cw 52, cl 40.5, ch 19.5, fw 16.5 mm), Fianarantsoa Province: region of Vondrozo near village of Vevembe (22 º 47 ' 44 "S, 47 º 11 ' 19 "E), Ramanara River, tributary of Sahampindra River, Mananara River drainage basin, 66.6 km inland from Farafangana, in a forested area in the mountains of southeastern Madagascar (M. Vences) (ZMA De. 205976). Additional material examined: MADAGASCAR: FMNH 5730, Sahavatov River, basin of Manampatrana River, Andringita Camp II, 1,390m asl (20 -Nov- 93); FMNH 5748, Sahambano River, Mananara-sud River drainage basin, Madagascar, 570 m asl, 25 -May- 95. Diagnosis. Terminal article of G 1 long (ratio of length of terminal article to subterminal segment 0.3), straight-sided cone, bent outward at 45 ° to longitudinal axis of gonopod, evenly-tapering to pointed tip; broad, diamond-shaped dorsal membrane at segment junction. Palm of propodus of major cheliped enlarged, dactylus slightly arched, enclosing long narrow interspace; propodus, and dactylus of major cheliped serrated, lined by small teeth interspersed by larger rounded teeth, with fused cluster of several small low teeth, tips pointed. Description of holotype. Carapace moderately wide (cw/fw 3.2) moderately high (ch/fw 1.2); anterolateral, posterolateral regions of carapace distinctly granular, with short carinae (Figs. 1, 16). Epigastric crests raised, anterior margins straight, positioned anterior to postorbital crests; mid-groove between epigastric crests broad, shallow; distinct gap between epigastric, postorbital crests; postorbital crests ending well before meeting anterolateral margins (Figs. 1, 2, 16). Semi-circular groove shallow, faint; urogastric, cardiac grooves shallow; cervical grooves long, ending before meeting postorbital crests (Figs. 1, 16). Front horizontal (not deflexed) leaving antennulular fossae exposed; upper edge of frontal margin granular, distinctly indented, lower edge V-shaped, broadest in middle, narrowest at sides; frontal margin of carapace approximately onethird cw (0.32) (Figs. 1, 2, 16, 17). Exorbital, epibranchial teeth large, pointed, directed forward, outer margins granular. Anterolateral margin between exorbital, epibranchial teeth lacking intermediate tooth (Figs. 1, 2, 16, 17). Anterolateral margin posterior to epibranchial tooth raised, with small teeth grading into heavy granules (Figs. 1, 16). Suborbital margin raised, heavily granulated (Figs. 2, 17). Suborbital, pterygomial regions of carapace sidewall heavily granulated, subhepatic region with carinae (Figs. 2, 17). Mandibular palp two-segmented, bilobed, with medium-sized anterior process (about one-third size of terminal segment). Ischium of third maxilliped with deep vertical sulcus (Fig. 17), exopod of third maxilliped with long flagellum (Fig. 7). Sternal sulci s 2 /s 3, s 3 /s 4 completely crossing sternum, s 3 /s 4 slightly V-shaped, not meeting anterior margin of sterno-abdominal cavity on sternite 4 (Fig. 8). Episternal sulci s 4 /e 4, s 5 /e 5, s 6 /e 6, s 7 /e 7 all smooth lacking visible groove (Fig. 8). Palm of propodus of major (left) cheliped enlarged, dactylus slightly arched, enclosing long rectangular interspace; fingers of major cheliped lined by small even teeth interspersed by large rounded teeth, propodus with fused cluster of three or four small low teeth (Figs. 3, 4). Walking legs (p 2 –p 5) of medium size (ratio of length of merus of p 5 to cw 0.40–0.45) (Fig. 16). Anterior inferior margin of ischium of pereiopod 1 granular; medial inferior margin of merus of pereiopod 1 heavily granulated, lateral inferior margin with several small teeth; distal meral tooth reduced to granule; superior surface of merus roughly granulated (Fig. 6). Inner margin of carpus of cheliped with two large, pointed carpal teeth, first tooth spine-like, second tooth one-third size of first, margin behind second tooth with small tooth (Fig. 5). Male abdomen long, slim, triangular (a 3 widest, a 6 shorter than width of distal margin of a 6), telson (a 7) bellshaped with indented sides. Terminal article of G 1 long (ratio of length of terminal article to subterminal segment 0.3), straight-sided cone, bent outward at 45 ° to longitudinal axis of gonopod, evenly-tapering to pointed tip (Figs. 9–15); no visible groove between terminal article and subterminal segment on ventral side (Figs. 9, 10); dorsal side with broad, diamond-shaped dorsal membrane at segment junction (Figs. 11, 14). Ventral side of subterminal segment of G 1 with long lateral flap folded inward; medial part of dorsal face of subterminal segment of G 1 flat with distinct disto-medial triangular shoulder, and large rounded baso-lateral projection (Fig. 10). G 2 longer than G 1; terminal article of G 2 long flagellum, ratio length terminal article to subterminal segment 0.8 (Fig. 9). Size. The largest specimen known is the holotype, an adult male, cw 52 mm. Color. In life, carapace purple-brown, lacking stains or spots, tips of chelipeds and pereiopods lighter shade of brown, granules on suborbital and pterygostomial regions of carapace sidewall beige. Type locality. Madagascar, Vevembe Forest (22 º 47 ' 44 "S, 47 º 11 ' 19 "E), 66.6 km inland from Farafangana in Fianarantsoa Province in a forested area in the mountains of southeastern Madagascar. Distribution. Endemic to Madagascar. Hydrothelphusa vencesi is known from three localities in southeastern Madagascar, two of them in the Mananara River drainage basin. The type locality is in the Vevembe Forest near the village of Vevembe in the region of Vondrozo in Fianarantsoa Province. This species is also found in the Sahavatov River which is part of the drainage basin of the Manampatrana River (Andringita Camp II, 1,390 m asl), and at 570 m asl in the Sahambano River in the basin of the Mananara-sud River. Remarks. The following morphological characters justify including H. vencesi in Hydrothelphusa (Cumberlidge & Sternberg 2002: 47; Thompson 2005). The carapace outline is transversely oval with wide frontal and posterior margins (each approximately one-third carapace width); the mandibular palp is two-segmented with a lobe-like, medium-sized anterior process (about one-third the size of the terminal segment) at the junction between the segments; the ischium of the third maxilliped has a deep vertical sulcus, and the exopod of the third maxilliped has a long flagellum; sternal sulcus s 2 /s 3 is deep and horizontal, and sternal sulcus s 3 /s 4 is shallow and V-shaped; episternal sulci s 4 /e 4, s 5 /e 5, s 6 /e 6, s 7 /e 7 are smooth and not visible; walking legs (p 2 –p 5) are neither shortened nor elongated, with the ratio of the length of the merus of p 5 to the cw of 0.40– 0.45; the male abdomen is long, slim, and triangular, with a bell-shaped telson whose sides are indented; the terminal article of G 1 is long (with a ratio of the length of the terminal article to the subterminal segment of 0.3); the subterminal segment of G 1 has a distinct disto-lateral triangular shoulder-like projection at the junction of the segments; and G 2 is longer than G 1 with a terminal article that has a long flagellum (the ratio of the length of the terminal article to the subterminal segment is approximately 0.8). Etymology. The species is named for Prof. Dr. Miguel Vences in recognition of his important contributions to our knowledge of the diversity, evolution, and natural history of Madgascar’s endemic fauna. Comparisons. Hydrothelphusa vencesi can be distinguished from other species of Hydrothelphsua (and indeed from all other Malagasy brachyurans) by examination of G 1 morphology (Figs. 10–15). The terminal article of G 1 of H. vencesi is a long straight-sided cone that tapers evenly to a pointed tip and lacks a pronounced raised mid section; in addition there is a broad diamond-shaped dorsal membrane at the segment junction on its dorsal side. These characters are unique to H. vencesi and set this taxon apart from the other species assigned to this genus (see below) (Cumberlidge & Sternberg 2002: 48–59, fig. 9 A–Q). Hydrothelphusa vencesi most closely resembles H. madagascariensis because these two large species share the following characters. The frontal margin, front behind the margin, and the suborbital, subhepatic, and pterygostomial regions of the carapace sidewall are all distinctly granulated, the exorbital and epibranchial teeth are both large and pointed, and the anterolateral margin behind the epibranchial tooth is either heavily granulated or toothed; the suborbital margin, the ischium of pereiopod 1, and the inferior margins of merus of pereiopod 1 are also granulated. Hydrothelphusa vencesi differs from H. madagascariensis in that the G 1 terminal article of H. vencesi is a long straight-sided evenly-tapering cone that lacks the pronounced raised mid-section seen in H. madagascariensis (Figs. 10–15; Cumberlidge & Sternberg 2002: figs. 9 E–I). Hydrothelphusa vencesi shares the following characters with H. bombetokensis. The exorbital and epibranchial teeth are both large and pointed and the first carpal tooth on the carpus of pereiopod 1 is a long, slen- der spine. Hydrothelphusa vencesi can be distinguished from H. bombetokensis as follows. The inferior margins of the merus of pereiopod 1 of H. bombetokensis are granular (whereas these margins in H. vencesi have several large and pointed teeth); the anterior carapace of H. bombetokensis is smooth (whereas that of H. vencesi is heavily granulated in the anterolateral corners and the frontal region); and the G 1 terminal article of H. bombetokensis is slim and distinctly raised in the mid-section (the result of a higher medial fold) ending in an upcurved tip (Cumberlidge & Sternberg 2002: figs. 9 J–M), whereas that of P. v e n c e s i is a long straightsided evenly-tapering cone that lacks the pronounced raised mid-section (Figs. 10–15). Hydrothelphusa vencesi is similar to H. agilis in that the frontal margin of both of these large species is noticeably indented in the middle. Hydrothelphusa vencesi can be distinguished from H. agilis as follows. The frontal margin is distinctly toothed in H. agilis but granular in H. vencesi; the inferior margin of the merus of pereiopod 1 of H. agilis has several large and pointed teeth, while these margins in H. vencesi are granular but not toothed; the suborbital margin and the p 1 ischium of H. agilis are both distinctly toothed, whereas these structures are granular in H. vencesi; and the terminal article of G 1 of H. agilis is slim and evenly proportioned along its entire length, ending in an upcurved tip (Cumberlidge & Sternberg 2002: figs. 9 A–D), whereas that of P. vencesi is a long straight-sided evenly-tapering cone (Figs. 10–15). Hydrothelphusa vencesi can be distinguished from H. goudoti as follows. The carapace of H. goudoti is wider (cw/fw 3.9) and more arched (ch/fw 1.6) than that of H. vencesi (cw/fw 3.2, ch/fw 1.2); the exorbital and epibranchial teeth of H. goudoti are both small and blunt, whereas these teeth in H. vencesi are large and pointed; the postfrontal crest of H. goudoti is incomplete (wherein epibranchial crests and postorbital crests are separate), whereas in H. vencesi the postfrontal crest is complete; and the terminal article of G 1 of H. goudoti is slim with a raised and rounded mesial lobe, ending in a broad straight tip (Cumberlidge & Sternberg 2002: figs. 9 N–Q), whereas that of P. v e n c e s i is a long straight-sided evenly-tapering cone (Figs. 10–15).Published as part of Cumberlidge, Neil, Marijnissen, Saskia A. E. & Thompson, Jonelle, 2007, Hydrothelphusa vencesi, a new species of freshwater crab (Brachyura: Potamoidea: Potamonautidae) from southeastern Madagascar., pp. 61-68 in Zootaxa 1524 on pages 62-67, DOI: 10.5281/zenodo.17749

Ecological correlates of species differences in the Lake Tanganyika crab radiation

Abstract The endemic crabs of Lake Tanganyika include a phenotypically diverse clade that exhibits recent divergence and low phylogenetic species resolution. There are indications that ecological niche segregation has played a prominent role in the divergence of this clade. We used habitat surveys, gut content analyses and stable isotope analyses to test the extent to which morphological species are ecologically different. Our data show some interspecific segregation in depth, substrate type and mean stable isotope signatures. At the same time, a considerable level of ecological niche overlap is evident among species of Platythelphusa that coexist in rocky littoral habitats. We consider these results in the framework of adaptive radiation theory, and we discuss general ramifications for the maintenance of species diversity in Lake Tanganyika

Ecology and conservation status of endemic freshwater crabs in Lake Tanganyika, Africa

Sedimentation resulting from riparian deforestation has a wide range of detrimental effects on aquatic biodiversity, but predicting the full consequences of such disturbances requires an understanding of the ecosystem’s key functional components. We investigated the ecology and response to sedimentation of the diverse, endemic freshwater crabs of Lake Tanganyika, which may occupy important positions in littoral foodwebs. Our surveys revealed crab distribution patterns to be patchy, and that crabs can be locally abundant (0-28 individuals m−2). Crab densities decreased with depth and the dry mass of crab assemblages ranged from 0.0 to 117.7 g m−2. Comparisons among sites revealed significant effects of sedimentation on crab assemblage evenness, but provided no evidence that sedimentation has altered densities, incidence or species richness. The resilience of crabs to sedimentation might be related to their intraspecific dietary breadth. Stable isotope data (δ13C and δ15N) from crabs and their potential food resources indicated differences in trophic roles among endemic crab species. Overall, crabs occupy higher trophic positions than most other invertebrates, and they draw upon both benthic and planktonic energy pathways. The high biomass and top-predator status of some crab species suggests the potential for cascading effects on organisms lower in the food web