Cymonomus mainbaza, Ahyong, Shane T., 2014

Ahyong, Shane T., 2014, Cymonomid crabs of the MAINBAZA Expedition (Decapoda: Brachyura), Zootaxa 3821 (3), pp. 384-390 : 384-387

Cymonomus mainbaza sp. nov.

( Fig. 1 , 2 )

Type material. HOLOTYPE: MNHN-IU-2013-11302, ovigerous female (cl 5.9 mm, pcl 5.5 mm, cw 6.3 mm), Mozambique Channel, 23°31.94–32.66’S, 36°02.64–02.00’E, 886–898 m, shrimp trawl, B. O. Vizconde de Eza, stn CP3140, coll. B. Richer de Forges & L. Corbari, 11 April 2009.

PARATYPES: AM P92553, ovigerous female paratype (cl 4.9 mm, pcl 4.6 mm, cw 5.3 mm), Mozambique Channel, 25°59.02–58.35’S, 34°45.94–47.02’E, 949–952 m, shrimp trawl, B. O. Vizconde de Eza, stn CP3170, coll. B. Richer de Forges & L. Corbari, 16 April 2009; MNHN-IU-2013-11303, female paratype (cl 5.4 mm, pcl 4.9 mm, cw 5.7 mm), Mozambique Channel, 23°33.51–35.21’S, 36°07.27–05.88’E, 1092–1195 m, trawl, B. O. Vizconde de Eza, stn CP3139, coll. B. Richer de Forges & L. Corbari, 11 April 2009.

Diagnosis. Carapace dorsal surface minutely granulate; cervical groove cervical groove shallow, weakly defined; fronto-orbital margin advanced slightly beyond anterolateral margins; lateral frontal projections slender, elongated, markedly longer than rostrum. Rostrum short, triangular, length about one-fourth length of eyestalks. Eyestalks distinctly divergent, immovably fused to carapace below rostral base. Maxilliped 3 exopod not overreaching apex of endopod merus. Pereopods finely and evenly granular, not serrated. Pereopod 3 merus slightly longer than pcl. Pereopod 5 merus, when folded against carapace, reaching anteriorly slightly beyond midlength of carapace. Abdomen of 6 free segments.

Description. Carapace quadrate, almost square, lateral margins slightly divergent posteriorly; regions and cervical groove shallow, weakly defined; short, slender anterolateral spine and smaller anterolaterally-directed spine on lateral margin behind anterolateral spine; lower pterygostomian region swollen; anterior and anterolateral surfaces with long, fine setae, other surfaces almost glabrous. Dorsal and lateral surfaces covered with minute granules, granules becoming acute and slightly more elongated anterolaterally. Fronto-orbital margin (excluding rostrum and lateral projections) advanced slightly beyond anterolateral margins; slightly exceeding half anterior carapace width; lateral frontal projections slender, elongated, situated below plane of rostrum, laterally spinulate, with acute apices, longer than rostrum. Rostrum short, 0.06–0.07 pcl; length about one-fourth length of eyestalks; triangular, tapering to acute apex, minutely granular laterally and dorsally. Eyestalks distinctly divergent, ventrally flattened, immovably fused to carapace below rostral base; not reaching anteriorly to end of antennular peduncle article 1; dorsally granular, margins spinulate; cornea apparently vestigial, not pigmented. Epistome smooth except for small cluster of granules at base of rostrum and mesial to base of antennules; small spine mesial to base of antenna.

Antennular peduncle 0.90 pcl; article 1 and 3 smooth; article 2 minutely granular. Basal antennal article fused to epistome; articles 2–4 irregularly granular or spinular; article 5 smooth.

Maxilliped 3 ischiobasis subquadrate, surface sparsely granular, lateral margin acutely granular or weakly spinular; shallow longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus slightly shorter than ischiobasis, about 2.5 times longer than wide (excluding spines); gently tapering distally to rounded apex; surface granular and spinulate; margins bluntly spinulate. Propodus and carpus sparsely spinulate. Dactylus conical, unarmed. Exopod granular, distally reaching as far as apex of endopod merus.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus finely granular. Carpus finely granular, dorsal margin with prominent spine and elongated granules. Palm surfaces with fine granules and few scattered acute granules or small spines, especially along flexor and extensor margins. Dactylus longer than upper palm length; with small proximal dorsal spine and granules; with faint longitudinal carina on outer surface, occlusal surfaces of dactylus and pollex crenulate, without gape when closed.

Pereopod 2 and 3 long, slender, sparsely setose, almost glabrous; all segments except dactylus finely, evenly granular, without spines or serrations; dactylus broadly curved, smooth, with longitudinal rib. Pereopod 3 longest, merus longer than pcl (1.06–1.15 pcl), as long as or slightly longer than cl (1.00–1.07 cl); dactylus slightly shorter than combined length of propodus and carpus.

Pereopod 4 and 5 finely granular, glabrous; longer than pereopod 3 merus; dactyli markedly shorter than propodi, falcate, apex corneous, 4 obliquely inclined, corneous spines on flexor margin. Pereopod 5 merus, when folded against carapace, reaching anteriorly slightly beyond midlength of carapace.

Thoracic sternites 3 and 4 granular; sternite 3 pentagonal, lateral margins subparallel; 1.4 times wider than long.

Female abdomen with 6 free segments (somites 1–5, pleotelson); surface granular, coarsest on somites 2 and 3; pleotelson subtriangular, margins sinuous, width about 1.8 times length, without any trace of demarcation between somite 6 and telson. Egg diameter 1.1 mm.

Etymology. Named after the expedition during which the type material was captured; used as a noun in apposition.

Remarks. Cymonomus mainbaza sp. nov. most closely resembles C. normani Lankester, 1903 from the northeastern Atlantic and C. hakuhoae Takeda & Moosa, 1990 from the Indo-West Pacific in sharing the combination of a granular carapace surface, well-developed lateral frontal projections, and a rostrum that is no longer than one-fourth as long as the eyestalks. Cymonomus mainbaza sp. nov. is readily separated from C. normani by having distinctly more finely and evenly granular surfaces of the carapace and pereopods, especially on the meri, carpi and propodi of the walking legs ( Fig. 1 A) (coarsely and acutely serrated extensor margins of these segments in C. normani ; see Lankester 1903: pl. 33: fig. 1). Cymonomus mainbaza sp. nov. is readily distinguished from C. hakuhoae by its strongly divergent eyestalks (Fig. fig. 1A, B) (compared to subparallel or slightly divergent in C. hakuhoae ; see Ahyong & Ng 2009: fig. 4A, 5A) and the shorter maxilliped 3 merus that reaches distally to about the level of the apex of the exopod (distinctly overreaching the exopod in C. hakuhoae ). The pereopod 3 merus of C. mainbaza sp. nov. is also proportionally slightly longer than in C. hakuhoae (in females, about 1.1 pcl versus shorter than or as long as pcl 0.9–1.0 pcl in C. hakuhoae ).

Variation in the type series of C. mainbaza sp. nov. is slight; the rostral length varies from 0.06–0.10 pcl and the small spine on the margin behind the anterolateral spine of the carapace is more distinct in the paratypes than in the holotype, the largest specimen of the type series. The three known specimens are mature females of which one is spent; the other two are ovigerous, carrying 17 and 19 eggs, respectively, 1.1 mm in diameter.

Distribution. Presently known only from the Mozambique Channel, 886–1195 m.

Figures

FIGURE 1. Cymonomus mainbaza sp. nov., female holotype, cl 5.9 mm, pcl 5.5 mm, cw 6.3 mm, CP 3140 (MNHN-IU- 2013 - 11302). A, dorsal habitus; B, anterior carapace; C, right basal antennal spine; D, right maxilliped 3; E, sternite 3; F, abdominal somites 4, 5 and pleotelson; G, right pereopod 4 dactylus. Scale: A, F = 2.0 mm; C – E = 1.0 mm; G = 0.5 mm.

FIGURE 2. Cymonomus mainbaza sp. nov., female holotype, cl 5.9 mm, pcl 5.5 mm, cw 6.3 mm, CP 3140 (MNHN-IU- 2013 - 11302). Photo: T. Y. Chan.