Cymonomus umitakae Takeda, 1981

Ahyong, Shane T. & Ng, Peter K. L., 2017, Zavreliella undetermined, Zoological Studies (Zool. Stud.) 56 (24), pp. 1-20 : 15-18

Cymonomus umitakae Takeda, 1981

( Fig. 6 )

Cymonomus umitakae Takeda, 1981: 38-39 , fig. 1, 2 [type locality: E of Nojima-zaki, Bôsô Peninsula, Japan]. - Nagai 1991: 31, fig. 1a. - Takeda 2001: 224. - Ahyong and Brown 2003: 1373. - Ng et al. 2008: 32.

Cymonomus sagamiensis Sakai, 1983: 4 , pl. 8A. [type locality: E of Nojima-zaki, Bôsô Peninsula, Japan, by present neotype selection]. - Nagai 1989: 43. - Takeda 1997: 233. - Ahyong and Brown 2003: 1373. - Ng et al. 2008: 32.

Type material: HOLOTYPE: NSMT-Cr7437, female (cl 2.9 mm, pcl 2.5 mm, cw 2.8 mm), E of Nojima-zaki , Bôsô Peninsula, 34°57.5-57.7'N, 140°07.5-07.4'E, 260-335 m, RV Umitaka-Maru, stn UM-79068, 7 August 1979.

Other material examined: JAPAN: NSMT Cr12943, 1 male (cl 4.0 mm, pcl 3.4 mm, cw 3.7 mm), Tosa Bay, Japan, 33°11.2'N, 133°35.0- 34.3'E, 290- 257 m, RV Kotaka-Maru, stn K98- 6-300, 8 June 1998; WPMNH #48, 1 ovigerous female (cl 4.2 mm, pcl 3.9 mm, cw 4.6 mm), SE of Kuroshima Island, Okinawa, 300 m, 25 March 1990; WPMNH #49, 2 males (cl 2.8 mm, pcl 2.3 mm, cw 2.5 mm to cl 3.1 mm, pcl 2.6 mm, cw 2.7 mm), 6 females (cl 2.6 mm, pcl 2.2 mm, cw 2.5 mm to cl 3.8 mm, pcl 3.2 mm, cw 3.8 mm; 2 specimens with rhizocephalan externa under abdomen), off Cape Shionomisaki, Kii Peninsula, Wakayama Prefecture, 300-350 m, trawl, 14 September 1990.

Description: Carapace quadrate, almost square, lateral margins subparallel; regions weakly indicated; anterolateral margins with 2 prominent slender spines, shorter spinules, acute granules in addition to longer dorsal spine near anterolateral corner; anterior carapace margin mesial to the anterolateral spines sloping posteriorly; lower pterygostomian region swollen; anterior and anterolateral surfaces with few long, fine setae, other surfaces sparsely setose. Dorsal surfaces covered with minute granules and spinules, spinules most elongate anterolaterally and posteriorly. Fronto-orbital margin (excluding rostrum and lateral projections) slightly advanced beyond anterolateral margins; slightly wider than half anterior carapace width; outer orbital processes sharply triangular, elongate, divergent, directed anterolaterally, situated below plane of rostrum, laterally spinulate, with acute apices, as long as rostrum. Rostrum length slightly less than half to two-thirds length of eyestalks; 0.15- 0.22 pcl; slender, sharply triangular, spinose dorsally and laterally; slightly deflected ventrally. Eyestalks slightly divergent, ventrally flattened, slightly movable; reaching anteriorly three-fourths length of antennular peduncle article 1; dorsal surface acutely granulate, lateral and mesial margins spinulate; cornea apparently vestigial, not pigmented. Epistome smooth except for blunt tubercle mesial to base of antennule, with small spine mesial to base of antenna.

Antennular peduncle 1.07-1.13 pcl (male), 0.81-0.87 pcl (female); articles 1 and 2 minutely granular; article 3 smooth. Basal antennal article fused to epistome; article 2 spinose; remaining articles smooth or minutely granular.

Maxilliped 3 ischiobasis subquadrate, surface sparsely granular, lateral margin with few acute granules or short spines; with shallow longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus shorter than ischiobasis, length about 2.3 × width (excluding spines); tapering distally to rounded apex; surface and margins spinulate. Dactylus, propodus and carpus spinulate. Exopod sparsely but coarsely granular, distally overreaching merus of endopod.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus finely granular, with few short distoventral spines. Carpus prominently spinose, spines long, slender. Palm surfaces with long, slender spines, longest along flexor and extensor margins, extending onto pollex. Dactylus longer than upper palm length; proximal two-thirds spinose; outer surface with faint longitudinal carina, occlusal surfaces of dactylus and pollex crenulate, without gape when fingers closed.

Pereopods 2 and 3, sparsely setose, granular and spinose; longest spines on extensor margins and dorsal surfaces of propodus and carpus; merus extensor and flexor margins spinose, longest along proximal flexor margin, dorsal surfaces granular and with few small spines. Pereopod 3 longest, merus shorter than carapace, 0.91-0.98 pcl (males), 0.79-0.92 (females). Dactyli broadly curved, sparsely spinose proximally, otherwise smooth, without longitudinal rib. Pereopod 3 dactylus almost as long as combined length of propodus and carpus.

Pereopods 4 and 5 finely granular, and sparsely spinose; longer than pereopod 3 merus; dactyli markedly shorter than propodi, falcate, with corneous apex and 3 or 4 obliquely inclined, corneous spines on flexor margin. Pereopod 5 merus, when folded against carapace, reaching midlength of carapace.

Thoracic sternite 3 sparsely granular, about 1.7 × wider than long; sternite 3 pentagonal, lateral margins posteriorly subparallel. Margins of sternites 4 and 5 granulate.

Abdomen granulate and spinose, most prominent on somites 2 and 3, sparsely ornamented on somites 4 and 5; pleotelson subtriangular, sparsely granular or minutely spinose; margins straight to slightly convex, wider than long, width 1.6-1.7 × length (male), 1.8 (female); without any trace of demarcation between somite 6 and telson.

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

Remarks: Takeda (1981) described C. umitakae on the basis of a single incomplete female, lacking all pereopods except the left cheliped. The series examined here enables a good characterisation of the species based on both sexes. The combination of slender, weakly divergent ocular peduncles, a slender sharp rostrum, sharply triangular outerorbital processes of similar length to the rostrum, the anterior carapace margin mesial to the anterolateral processes sloping posteriorly inwards, and prominently spinose carpi and propodi of pereopods 2 and 3 is shared by C. umitakae and C. valdiviae from off east Africa ( Ahyong 2014). Cymonomus umitakae is readily distinguished from C. valdiviae by the more slender distal articles of the antennular peduncle (penultimate article length not more than twice width versus three times width in C. valdiviae and the proportionally shorter walking legs (0.79-0.89 pcl in females versus 0.94- 0.97 pcl in female C. valdiviae ) ( Fig. 6A, B ; Ahyong 2014: fig. 3A).

Variation within the present series of C. umitakae is slight, chiefly evident in the dorsal spination of the carapace and marginal spination of the eyestalks and rostrum - most pronounced in the largest specimens. The telson of the smallest male is apparently yet to reach adult form, having less rounded anterolateral corners. Sexual dimorphism is as observed in other congeners in proportionally longer walking legs and antennules in males. Two females ( WPMNH #49) are parasitized, having a rhizocephalan externa under the abdomen. The abdomen of the smallest male (pcl 2.3 mm, incompletely developed gonopods) is more evenly rounded than in adult males in which the telson is distinctly triangular.

Sakai (1983) described Cymonomus sagamiensis from the Kumano Sea, Mie Prefecture, based on a single dried carapace. Unfortunately, the description was extremely brief, and the figure rudimentary. Searches of Japanese museum collections over the past 15 years as well as the Natur-Museum und Forschungsinstitut Senckenberg, Frankfurt am Main, where some of Sakai’s material is deposited failed to locate the holotype of C. sagamiensis ; it is considered lost. Sakai (1983) considered C. sagamiensis to probably represent the species reported by him in 1976 as C. andamanicus (herein referred to C. cognatus ). Sakai’s (1976: pl. 8 fig. 1) figure, however, bears little resemblance to the holotype description of C. sagamiensis or figure ( Sakai 1983: pl. 8A), especially in the short rostrum, and subparallel eyestalks. Rather, Sakai’s (1983) figure resembles C. umitakae , unique in the Japanese fauna for its subparallel eyes, and strong anterolateral spines on the carapace. Indeed, Takeda (1997) also noted the similarity between C. umitakae and C. sagamiensis . We regard C. sagamiensis and C. umitakae as synonymous, and herein designate the holotype of the latter as the neotype of the former in order to stabilise the identity of Sakai’s species. Thus, C. sagamiensis becomes an objective junior synonym of C. umitakae .

Distribution: Southeastern Japan, from E of Nojima-zaki, Suruga Bay and Tosa Bay to Okinawa; 219- 500 m.

Figures

Fig. 6. Cymonomus umitakae Takeda, 1981, Japan. A-F, female, cl 3.8 mm, pcl 3.2 mm, cw 3.8 mm, WPMNH #49; G-I: male, cl 3.1 mm, pcl 2.6 mm, cw 2.7 mm, WPMNH #49; J, female holotype, cl 2.9 mm, pcl 2.5 mm, cw 2.8 mm, NSMT Cr7437. A, dorsal habitus; B, fronto-orbital region; C, right basal antennal spine; D, right maxilliped 3; E, thoracic sternite 3; F, abdomen, posterior; G, right gonopod 1, abdominal view; H, right gonopod 2, abdominal view; I-J, telson. Scale bars: A, F, I, J = 1.0 mm; B-E, G, H = 0.5 mm.