Cymonomus valdiviae Lankester, 1903

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

Cymonomus valdiviae Lankester, 1903

( Fig. 3 )

Cymonomus Valdiviae Lankester, 1903: 458 , 459, fig. 11.

Cymonomus granulatus . — Doflein, 1904: 33, pl. 11: fig. 5, pl. 12: figs. 1–3, pl. 38: fig. 8. Cymonomus granulatus Valdiviae. — Doflein, 1904: 284.

Cymonomus valdiviae . — Dell, 1971: 63. — Tavares, 1993: 254, 255, 258, 260. Cymonomoides valdiviae . — Ahyong & Brown, 2003: 1372. — Ng et al. 2008: 32.

Type material. HOLOTYPE: ZMB 13614, ovigerous female (badly damaged, abdomen only, with 6 eggs), off southern Somalia, 0°27.4'S, 42°47.8'E, Deutsche Tiefsee-Expedition Sta. 253, 638 m.

Other material examined. MNHN-IU-2013-11304, 1 ovigerous female (cl 4.1 mm, pcl 3.5 mm, cw 3.9 mm), Mozambique Channel, 19°34.3–35.31’S, 36°46.53–45.72’E, 518–524 m, shrimp trawl, B. O. Vizconde de Eza, stn CC3153, coll. B. Richer de Forges & L. Corbari, 13 April 2009; AM P92554, 1 spent female (cl 3.5 mm, pcl 3.0 mm, cw 3.4 mm), same.

Diagnosis. Carapace dorsal surface minutely granulate; 5 or 6 spines on anterolateral margin; cervical groove scarcely indicated; fronto-orbital margin distinctly advanced beyond anterolateral margins; lateral frontal projections slender, elongated, slightly shorter than rostrum. Rostrum slender, about three-fourths length of eyestalks. Eyestalks subparallel, slightly movable. Maxilliped 3 exopod not reaching apex of endopod merus. Pereopods 2 and 3 propodus and carpus with spinular margins. Pereopod 3 merus slightly shorter than pcl. Pereopod 5 merus, when folded against carapace, reaching midlength of carapace. Abdomen of 6 free segments.

Description. Carapace quadrate, almost square, lateral margins slightly subparallel; cervical groove and regions scarcely indicated; anterolateral margins with 5 or 6 slender spines, smaller spinules and acute granules; lower pterygostomian region swollen; anterior and anterolateral surfaces with long, fine setae, other surfaces sparsely setose. Dorsal surfaces covered with minute granules, with granules becoming acute, more elongate anterolaterally. Fronto-orbital margin (excluding rostrum and lateral projections) distinctly advanced beyond anterolateral margins; half anterior carapace width; lateral frontal projections triangular, elongate, situated below plane of rostrum, laterally spinulate, with acute apices, slightly shorter than rostrum. Rostrum 0.15–0.19 pcl; length about about three-fourths length of eyestalks; slender, tapering to acute apex, minutely spinulate laterally. Eyestalks slightly divergent, ventrally flattened, slightly movable; reaching to anterior two-thirds length of antennular peduncle article 1; dorsal surface and margins spinulate; cornea apparently vestigial, not pigmented. Epistome smooth except for blunt tubercle mesial to base of antennule and small spine mesial to base of antenna.

Antennular peduncle 0.86 pcl; articles 1 and 2 minutely granular; article 3 smooth. Basal antennal article fused to epistome; article 2 spinular; remaining articles smooth or minutely granular.

Maxilliped 3 ischiobasis subquadrate, surface sparsely granular, lateral margin with few acute granules or short spines; shallow longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus as long as ischiobasis, about 2.4 times longer than wide (excluding spines); tapering distally to rounded apex; surface sparsely granular or spinulate; margins spinulate. Propodus and carpus sparsely spinulate. Dactylus conical, unarmed. Exopod sparsely granular and spinular, distally overreaching merus of endopod.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus finely granular, with few small distal spines. Carpus finely granular and spinular, dorsal margin with long prominent spine and scattered smaller spines. Palm surfaces with fine granules and slender spines, longest along flexor and extensor margins. Dactylus longer than upper palm length; proximally spinose; smooth outer surface, occlusal surfaces of dactylus and pollex crenulate, without gape when closed.

Pereopod 2 and 3, slender, sparsely setose, granular and spinose; longest spines on extensor margins of propodus and carpus; merus extensor and flexor margins with short spines; dactylus broadly curved, sparsely spinose proximally, otherwise smooth, without longitudinal rib. Pereopod 3 longest, merus slightly shorter than carapace (0.94–0.97 pcl); dactylus slightly shorter than combined length of propodus and carpus.

Pereopods 4 and 5 finely granular, sparsely spinose; longer than pereopod 3 merus; dactylus markedly shorter than propodus, falcate, with corneous apex and 2 or 3 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 sparsely granular; sternite 3 pentagonal, lateral margins posteriorly divergent, 1.5 times wider than long.

Female abdomen with 6 free segments (somites 1–5, pleotelson); surface of somites 2 and 3 spinose, others finely and sparsely granular; pleotelson subtriangular, margins weakly concave, wider than long, width 1.5–1.7 width, without any trace of demarcation between somite 6 and telson. Egg diameter 0.9 mm.

Remarks. Cymonomus valdiviae Lankester, 1903 , was until now known only from the ovigerous holotype collected off southern Somalia. The holotype of C. valdiviae is unfortunately badly damaged. Only the abdomen is now extant; presumably, the specimen was dissected as part of Doflein's (1903) study of deep-water brachyuran eyes. The new specimens, however, permit a redescription of this little known species. The only other published report of C. valdiviae , that of Ihle (1918) from Indonesia, is referrable to C. deforgesi Ahyong & Ng, 2009 or a similar species ( Ahyong & Ng 2009). Cymonomus valdiviae is readily distinguished from the two other known western Indian Ocean species by its rostral length: three-fourths eyestalk length compared to being about onefourth eyestalk length in C. mainbaza sp. nov. and longer than the eyestalks in C. trifurcus .

Ahyong & Brown (2003) tentatively transferred Cymonomus valdiviae to Cymonomoides Tavares (1993) on the basis of what appeared to be a 7- rather than 6-segmented abdomen (telson and somite 6 fused) in Doflein's (1904: pl. 12, fig. 2) ventral figure of the holotype (under the name C. granulatus (Norman in Thomson, 1873)). Re-examination of the abdomen of the holotype of C. valdiviae and the newly collected specimens shows that the abdomen is actually 6-segmented corresponding to Cymonomus sensu stricto. The posterior end of the abdomen, which appeared to represent a separate telson in Doflein's figures, is actually indistinguishably fused with somite 6 forming a pleotelson ( Fig. 3 H, F); the apparent line of demarcation between the telson and somite 6 in Doflein's figure may derive from clumped marginal setae lying across the pleotelson surface, detritus, or the result of an artist's erroneous attempt at photographic enhancement. Ahyong & Ng (2009), nevertheless, showed that the male abdominal segmentation does not reliably separate Cymonomus from Cymonomoides , suggesting that the latter is probably a synonym of the former.

Distribution. Presently known only off eastern Africa from southern Somalia to Mozambique; 518– 638 m.

Figures

FIGURE 3. Cymonomus valdiviae Lankester, 1903: A – F, ovigerous female, cl 4.1 mm, pcl 3.5 mm, cw 3.9 mm, CC 3153 (MNHN-IU- 2013 - 11304); G, ovigerous female holotype (ZMB 13614). 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 5 dactylus; H, pleotelson. Scale: A, F, H = 2.0 mm; C – E = 1.0 mm; G = 0.5 mm.