Cymonomus japonicus Balss, 1922

Ahyong, Shane T. & Ng, Peter K. L., 2017, Zavreliella undetermined, Zoological Studies (Zool. Stud.) 56 (24), pp. 1-20 : 12-15

Cymonomus japonicus Balss, 1922

( Fig. 5 )

Cymonomus granulatus japonicus Balss, 1922: 117-118 , fig. 5 [type locality: off Shionomisaki, Kii Peninsula, Japan; fixed by present neotype designation]. - Griffin and Brown 1976: 252. - Sakai 1976: 36, fig. 20. - Nagai 1991: 32, fig. 1b.

Cymonomus japonicus . - Takeda 2001: 224. - Ahyong and Brown 2003: 1372. - Ng et al. 2008: 32.

Type material: NEOTYPE: WPMNH #47 (part), female (cl 5.9 mm, pcl 4.6 mm, cw 5.0 mm), off Shionomisaki , Kii Peninsula, Wakayama Prefecture, Japan, 500 m, 1990.

Other material examined: JAPAN: WPMNH #47 (part), 4 males (cl 4.9 mm, pcl 3.8 mm, cw 3.8 mm to cl 5.2 mm, pcl 3.9 mm, cw 3.8 mm), collected with neotype.

Description: Carapace quadrate, almost square, lateral margins almost parallel; regions weakly indicated, cervical groove more pronounced in males than females, broadly V-shaped; with slender conical anteriorly directed anterolateral spine and similar anterolaterally directed spine on lateral margin behind anterolateral spine; lower pterygostomian region swollen; anterolateral surfaces with few scattered setae. Dorsal and lateral surfaces entirely covered with minute rounded granules, with granules becoming larger more elongate anterolaterally, conical or subcylindrical, not globose. Fronto-orbital margin (excluding rostrum and lateral projections) slightly advanced beyond anterolateral margins, more pronounced in males than females; exceeding half anterior carapace width; outer orbital processes slender, elongate, directed anteriorly, situated below plane of rostrum, laterally spinulate, with acute apices, up to half rostral length. Rostrum slightly longer than eyestalks; 0.26- 0.32 pcl; slender, tapering to acute apex, granular dorsally, minutely spinular laterally. Eyestalks distinctly divergent, stout, flattened, granular and prominently spinulate, fused to carapace below rostral base but demarcation distinct, reaching anteriorly to midlength of antennular peduncle article 1; cornea apparently vestigial, not pigmented. Epistome surface granulate, with blunt tubercle mesial to base of antennules, small spine mesial to base of antenna, with small cluster of elongate granules at base of rostrum.

Antennular peduncle 0.97-1.02 pcl (male), 0.79 pcl (female); articles 1 and 2 minutely spinular; article 3 minutely granular. Basal antennal article fused to epistome; articles 2-5 irregularly granular or spinular.

Maxilliped 3 ischiobasis subquadrate, sparsely granular and spinular, with longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus slightly shorter than ischiobasis, length about twice width, tapering distally to rounded apex; surface and margins spinulate. Dactylus conical, unarmed; propodus and carpus sparsely spinulate. Exopod sparsely granular, reaching beyond carpo-meral articulation but not reaching end of merus of endopod.

Chelipeds (pereopod 1) equal in size and ornamentation, setose. Merus finely granular proximally, spinose distally. Carpus granular, dorsal margin with 3 spines. Palm surfaces granular, flexor and extensor margins with tubular and club-shaped tubercles. Dactylus slightly longer than upper palm length; proximal dorsal half with club-shaped tubercles; with faint longitudinal carina on outer surface, occlusal surfaces of dactylus and pollex crenulate, without gape when fingers closed.

Pereopods 2 and 3 sparsely setose; all articles except for dactylus finely granular; propodus and carpus with blunt spinular extensor margins; merus with blunt spinular extensor and flexor margins. Pereopod 3 longest, merus 1.15- 1.28 pcl (male), 1.12 pcl (female). Dactyli broadly curved, smooth, with longitudinal rib. Pereopod 3 dactylus longer than combined length of propodus and carpus. Pereopods 4 and 5 coarsely granular, some small spines, sparsely setose; shorter than merus of pereopod 3; dactyli markedly shorter than propodi, falcate, with corneous apex and 2 or 3 obliquely inclined, corneous spines on flexor margin. Pereopod 5 merus, when folded against carapace, reaching midlength of carapace.

Thoracic sternite 3 pentagonal, about 1.5 × wider than long; lateral margins subparallel, irregular, surface granulate. Margins of sternites 4 and 5 granulate.

Abdomen of both sexes with margins and surface finely granular or minutely spinulate; pleotelson or both sexes distally obtuse, bluntly rounded, length slightly exceeding half width.

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

Remarks: Cymonomus japonicus was originally described as a subspecies of C. granulatus based on a single male collected from Haidashi Bank, Sagami Bay (600 m). To date, C. japonicus has been reported only twice since it was described in 1922: Takeda (2001) from Tosa Bay (528-537 m), and Nagai (1991) from off Shionomisaki (500 m). Cymonomus japonicus is the only known Japanese species with a ‘long’ rostrum, and on this basis (together with agreement with the brief type description and figure), the present specimens are identified with Balss’ species. Other similar ‘long’ rostrum species, however, occur in the western Pacific, such as C. indicus Ihle, 1916 , from Indonesia and a possibly undescribed species from the Solomon Islands (Ahyong, unpublished data); although distinct from the present Japanese material, the Indonesian and the Solomon Islands specimens also fit Balss’ account of C. japonicus . Extensive searches over the past 15 years of museum collections in which Balss’ material may be housed (Naturalis, Leiden; the Natural History Museum, London; Muséum national d’Histoire Naturelle, Paris; Zoologisches Museum an der Humboldt-Universität, Berlin; Natur-Museum und Forschungsinstitut Senckenberg, Frankfurt am Main; Zoologisches Institut and Zoologisches Museum, Hamburg; Zoologische Staatssammlung, Munich) failed to locate the holotype of C. japonicus ; it must therefore be considered lost. To fix the identity of the species and allow us to clarify the taxonomy of allied taxa, we designate the largest specimen in the present series as the neotype of C. japonicus (female, cl 5.9 mm, pcl 4.6 mm, cw 5.0 mm; WPMNH #47). Although not from the original type locality (Sagami Bay), the neotype locality (Kii Peninsula) is geographically close to Sagami Bay and well within the expected range of the species.

Aside from normal sexual dimorphism, the most notable variation in the present series is the proportional length of the eyestalks (proportionally shortest in the largest specimens). The eyestalks anteriorly exceed the outer orbital processes by half the eyestalk length in the smallest individual to only slightly in the largest individual; the specimens otherwise agree well.

Cymonomus japonicus belongs to the C. granulatus group ( Dell 1971) in having an elongate rostrum that distinctly overreaches the eyes, and prominently developed, spinose outer orbital processes. Other species in the C. granulatus group are as C. aequilonius Dell, 1971 ( New Zealand), C. granulatus (Norman in Wyville Thomson, 1873) (northeast Atlantic), C. indicus Ihle, 1916 ( Indonesia), and C. magnirostris Tavares, 1991 ( Brazil). Cymonomus japonicus is readily separated from C. magnirostris by the shorter maxilliped 3 exopod ( Fig. 5E ) (not overreaching the distal end of the merus versus distinctly overreaching the merus; Tavares 1991: fig. 8E) and shorter pereopod 5 ( Fig. 5A ) (merus reaching to midlength of carapace instead of anterior one-fourth; Tavares 1991: fig. 10F); and from C. granulatus by the slender versus triangular rostrum with basal width of about half the length ( Fig. 5A, B, K, L ; Mura and Cau 2003: fig. 2). From C. indicus and C. aequilonius , C japonicus can be separated by the differences in the shape of the dorsal carapace tubercles (rounded versus polygonal or stellate in C. indicus ). Cymonomus japonicus differs from C. aequilonius in having more pronounced, coarser surface granulation and in the shorter pereopod 4, reaching to the carapace midlength rather than anterior one-fourth ( Fig. 5A ; Ahyong 2008: fig. 1F).

Distribution: Known only from southeastern Japan: Sagami Bay (600 m), Shionomisaki (500 m) and Tosa Bay (528-537 m); 500-600 m depth.

Figures

Fig. 5. Cymonomus japonicus Balss, 1922, Japan, WPMNH #47. A-G: female neotype, cl 5.9 mm, pcl 4.6 mm, cw 5.0 mm; H-J: male, cl 4.8 mm, pcl 3.7 mm, cw 3.8 mm; K: male, cl 4.0 mm, pcl 3.9 mm, cw 3.8 mm; L, male, cl 5.0 mm, pcl 3.9 mm, cw 3.8 mm. A, dorsal habitus; B, K, L, fronto-orbital region; C, right basal antennal spine; D, carapace tubercles of right anterolateral corner; E, right maxilliped 3; F, thoracic sternite 3; G, abdomen, posterior; H, telson; I, right gonopod 1, abdominal view; J, right gonopod 2, abdominal view. Scale bars: A, G = 2.0 mm; B, E, F, H-L = 1.0 mm; C, D = 0.5 mm.