Hydrothelphusa vencesi, Cumberlidge, Neil, Marijnissen, Saskia A. E. & Thompson, Jonelle, 2007

Cumberlidge, Neil, Marijnissen, Saskia A. E. & Thompson, Jonelle, 2007, Hydrothelphusa vencesi, a new species of freshwater crab (Brachyura: Potamoidea: Potamonautidae) from southeastern Madagascar., Zootaxa 1524, pp. 61-68 : 62-67

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 (22º47'44"S, 47º11'19"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 G1 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 s2/s3, s3/s4 completely crossing sternum, s3/s4 slightly V-shaped, not meeting anterior margin of sterno-abdominal cavity on sternite 4 ( Fig. 8 ). Episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 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 (p2–p5) of medium size (ratio of length of merus of p5 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 (a3 widest, a6 shorter than width of distal margin of a6), telson (a7) bellshaped with indented sides. Terminal article of G1 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 G1 with long lateral flap folded inward; medial part of dorsal face of subterminal segment of G1 flat with distinct disto-medial triangular shoulder, and large rounded baso-lateral projection ( Fig. 10 ). G2 longer than G1; terminal article of G2 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 (22º47'44"S, 47º11'19"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 s2/s3 is deep and horizontal, and sternal sulcus s3/s4 is shallow and V-shaped; episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 are smooth and not visible; walking legs (p2–p5) are neither shortened nor elongated, with the ratio of the length of the merus of p5 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 G1 is long (with a ratio of the length of the terminal article to the subterminal segment of 0.3); the subterminal segment of G1 has a distinct disto-lateral triangular shoulder-like projection at the junction of the segments; and G2 is longer than G1 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 G1 morphology ( Figs. 10–15 ). The terminal article of G1 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. 9A–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 G1 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. 9E–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 G1 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. 9J–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 p1 ischium of H. agilis are both distinctly toothed, whereas these structures are granular in H. vencesi ; and the terminal article of G1 of H. agilis is slim and evenly proportioned along its entire length, ending in an upcurved tip (Cumberlidge & Sternberg 2002: figs. 9A–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 G1 of H. goudoti is slim with a raised and rounded mesial lobe, ending in a broad straight tip (Cumberlidge & Sternberg 2002: figs. 9N–Q), whereas that of P. v e n c e s i is a long straight-sided evenly-tapering cone ( Figs. 10–15 ).

Figures

FIGURES 1 – 9. Hydrothelphsua vencesi n. sp., adult male holotype (cw 52 mm, ZMA De. 205976) from Vevembe, Fianarantsoa Province, Madagascar. 1, carapace and eyes, dorsal view; 2, cephalothorax, carapace and eyes, frontal view; 3, right cheliped, frontal view; 4, left cheliped, frontal view; 5, carpus and merus of right cheliped, dorsal view; 6, merus of right cheliped, inferior view; 7, left third maxilliped; 8, sternum and abdomen; 9, abdomen pulled back to show first and second gonopods. Scale = 13 mm (1,2, 8, 9); 7 mm (3 – 7).

FIGURES 10 – 15. Hydrothelphsua vencesi n. sp., adult male holotype (cw 52 mm, ZMA De. 205976) from Vevembe, Fianarantsoa Province, Madagascar. 10, right G 1, ventral view; 11, right G 1, dorsal view; 12, terminal article of right G 1, dorsal view; 13, detail of tip of terminal article of right G 1, dorsal view; 14, detail of tip of terminal article of right G 1, dorsal view; 15, right first gonopod turned to show detail of tip of terminal article. Scale = 7 mm (10, 11); 2 mm (12 – 15).

FIGURES 16 – 17. Hydrothelphsua vencesi n. sp., adult male holotype (cw 52 mm, ZMA De. 205976) from Vevembe, Fianarantsoa Province, Madagascar. 16, whole animal dorsal view; 17, detail of eyes and mouthparts, frontal view.