Cymonomus curvirostris Sakai, 1965

Ahyong, Shane T. & Ng, Peter K. L., 2017, Zavreliella undetermined, Zoological Studies (Zool. Stud.) 56 (24), pp. 1-20 : 7-9

Cymonomus curvirostris Sakai, 1965

( Figs. 3 , 7D )

Cymonomus granulatus curvirostris Sakai, 1965: 19-20 , fig. 2, pl. 10 fig 1. [type locality: SW of Jogashima, Japan]. - Griffin and Brown 1976: 252. - Sakai 1976: 36, pl. 7 fig. 3. - Nagai 1989: 43.

Cymonomus curvirostris . - Takeda 2001: 223. - Ahyong and Brown 2003: 1372, 1374. - Ng et al. 2008: 32.

Type material: HOLOTYPE: NSMT-Cr R3850 , ovigerous female (cl 3.3 mm, pcl 3.0 mm, cw 3.3 mm), 2.5 miles SW of Jogashima Light House, Sagami Bay , 100 m, 6 Dec 1961.

Other material examined: CBM-ZC 6450, 1 male (cl 3.0 mm, pcl 2.6 mm, cw 2.8 mm), 1 ovigerous female (cl 3.7 mm, pcl 3.1 mm, cw 3.7 mm), Sagami Bay, off Misaki, Miura, Kanagawa Prefecture, 35°08.09'N, 129°32.92'E, 240-418 m, sand, dredge, RV Rinkai-maru, University of Tokyo, coll. T. Komai, 27 February 2002.

Description: Carapace quadrate, almost square, lateral margins slightly convergent anteriorly; regions weakly indicated; lower pterygostomian region swollen; anterior and anterolateral surfaces with few long, fine setae, other surfaces almost glabrous. Carapace surface densely covered with rounded tubercles; anterolateral and lateral surfaces with rounded or globular tubercles and granules, club-shaped or stalked, sometimes with minute apical point; tubercles largest anterolaterally; central carapace surface densely covered with rounded tubercles, almost entirely obscuring regions. Fronto-orbital margin (excluding rostrum and lateral projections) not advanced beyond anterolateral margins; width about half anterior carapace width; outer orbital processes elongate, directed anteriorly, situated below plane of rostrum, covered with club-shaped or stalked tubercles, as long as rostrum. Rostrum slender, apex blunt, with or without stalked tubercle, tuberculate or with slender projections laterally and dorsally; slightly longer than half length of eyestalks; 0.10-0.19 pcl. Eyestalks strongly divergent, flattened, fused to carapace below rostral base but demarcated from frontal margin; covered with stalked tubercles; reaching anteriorly to apex of basal antennular peduncle article. Epistome smooth except for blunt tubercle mesial to base of antennule, with small spine mesial to base of antenna.

Antennular peduncle 0.95 pcl (male), 0.75 pcl (female); articles minutely granular. Basal antennal article fused to epistome; articles 2-4 with globose tubercles or elongate; article 5 smooth.

Maxilliped 3 ischiobasis subquadrate, sparsely granular, with globose tubercles; ischiobasial demarcation indistinct. Merus slightly shorter than ischiobasis, almost 3.0 × longer than wide; tapering distally to rounded apex; surface and margins covered with globose and club-shaped tubercles. Dactylus, propodus and carpus sparsely spinulate or tuberculate. Exopod slightly exceeding merus of endopod; covered with globose and club-shaped tubercles.

Chelipeds sparsely setose; all articles densely covered with globose and club-shaped tubercles. Dactylus longer than upper palm length; with proximal dorsal granules or spinules in addition to small globose tubercles; occlusal surfaces of dactylus and pollex with scattered setae, with distinct gape when fingers closed.

Pereopods 2 and 3 sparsely setose; all articles except for dactylus with globose and club-shaped tubercles; on merus and propodus most pronounced along extensor and flexor margins; on carpus covering extensor margin and dorsal surface. Pereopod 3 longest, merus 1.11 pcl (male), 0.91-0.93 pcl (female). Dactyli broadly curved, extensor margin minutely granulate or spinulate proximally; with longitudinal rib, unarmed on pereopod 2, proximally spinulate on pereopod 3. Pereopod 3 dactylus as long as combined length of propodus and carpus.

Pereopods 4 and 5 with globose and club-shaped tubercles, and minute spinules, sparsely setose; longer than merus of pereopod 3; dactyli markedly shorter than propodi, falcate, flexor margin with 2 or 3 spinules. Pereopod 5 merus, when folded against carapace, reaching midlength of carapace.

Thoracic sternite 3 pentagonal, about 1.7 × wider than long; lateral margins divergent posteriorly, surface with small globose tubercles and granules, margins of sternites 4 and 5 with large, globose tubercles.

Abdomen densely covered with globose and club-shaped tubercles, and scattered spinules. Female pleotelson triangular, length about half width, apex rounded. Male pleotelson, length greater than half width.

Gonopod 1 distal article cannulate, forming copulatory tube, with long distal setae. Gonopod 2 with articles fused; distomesial margin slightly hollowed, apex acute.

Egg diameter 0.86-1.16 mm.

Remarks: Cymonomus curvirostris Sakai, 1965 , C. kapala Ahyong and Brown, 2003 , C. liui Ahyong and Ng, 2011 , C. mariveneae Ahyong and Ng, 2009 , and C. trifurcus Stebbing, 1920 , are herein referred to as the C. curvirostris group. The presence of large, globular pedunculate tubercles on the dorsal and the ventral surfaces of the cephalothorax, abdomen and pereopods distinguishes the members of the C. curvirostris group from all other congeners. Cymonomus curvirostris is readily distinguished from C. kapala (southeastern Australia) by the presence in the latter of a massive rounded boss on each branchial region ( Fig. 3A versus Ahyong and Brown 2003: fig. 1) and from C. trifurcus ( South Africa) by relatively short rostrum, shorter than the eyestalk in the former versus overreaching the eyestalk in the latter; Fig. 3A, B versus Barnard 1950: fig. 74A, C). The Japanese species differs from C. marivenae ( Philippines) by the ornamentation of the central surface of the carapace (entirely tuberculate versus smooth in C. marivenae ; Fig. 3A , Ahyong and Ng 2009: fig. 6A).

Cymonomus curvirostris is morphologically closest to C. liui from the Philippines, but is readily distinguished by the proportionally wider female pleotelson ( Fig. 3F ) (length half width versus two-thirds width in C. liui ; Ahyong and Ng 2011: fig. 3F), the shorter maxilliped 3 merus which does not overreach the exopod ( Fig. 3D ) (distinctly overreaching the exopod in C. liui ; Ahyong and Ng 2011: fig. 3D), and much more extensive, more prominent tuberculation on the carapace, abdomen and the pereopod 2-3 meri ( Fig. 3A ; cf. Ahyong and Ng 2011: fig. 3A). In Cymonomus curvirostris , the surfaces of the carapace and abdomen are almost entirely covered with tubercles ( Figs. 3A, F ) (more sparsely distributed in C. liui ; Ahyong and Ng 2011: fig. 3A, F) and the flexor and extensor margins of the pereopod 2-3 meri are entirely lined with club-shaped tubercles ( Figs. 3A, F ) (only sparsely so in C. liui ; Ahyong and Ng 2011: fig. 3A, F).

During preparation of the study, T. Komai forwarded us a colour photograph C. curvirostris collected recently from off Miura, Sagami Bay, Japan ( CBM, ovigerous female, cl 3.6 mm, pcl 3.3 mm, cw 3.9 mm 35°06.81'N, 139°33.78'E to 35°06.63'N, 139°33.73'E, 292-375 m, dredge, RV Rinkai-maru, coll. T. Komai, 15 February 2017); the image is shown in Fig. 7D .

Distribution: Known only from southeastern Japan: Sagami Bay (1 0 0-4 1 8 m), off Cape Shionomisaki (140-150 m; Nagai 1989) and Tosa Bay (232-850 m; Takeda 2001).

Figures

Fig. 3. Cymonomus curvirostris Sakai, 1965, Japan, CBM ZC 6450. A-F: female, cl 3.7 mm, pcl 3.1 mm, cw 3.7 mm; G-J: male, cl 3.0 mm, pcl 2.6 mm, cw 2.8 mm. A, dorsal habitus; B, fronto-orbital region; C, right basal antennal spine; D, right maxilliped 3; E, thoracic sternite 3; F, abdomen, posterior; G, telson; H, rostrum; I, right gonopod 1, abdominal view; J, right gonopod 2, abdominal view. Scale bars: A, F = 1.0 mm; B, D, E, H-J = 0.5 mm; C = 0.25 mm.

Fig. 7. A, Cymonomus chani sp. nov., female holotype, pcl 7.9 mm, SW of Kaohsiung, Taiwan, NTOU; B, Cymonomus cognatus sp. nov., male holotype, pcl 6.4 mm, E of Su-Ao, Taiwan, NTOU; C, Cymonomus cognatus sp. nov., spent female, pcl 9.2 mm, SE of Macclesfield Bank, stn DW4102, AM P100611; D, Cymonomus curvirostris Sakai, 1965, ovigerous female, pcl 3.3 mm, off Miura, Sagami Bay, Japan, CBM (specimen not examined); E, Cymonomus deforgesi Ahyong and Ng, 2009, male, pcl 5.5 mm, SW of Dongsha, stn CP4132, ZRC. Photos: A, B, C, E (T.Y. Chan), D (T. Komai).