Cymonomus bathamae Dell, 1971

Ahyong, Shane T., 2019, The Cymonomid Crabs of New Zealand and Australia (Crustacea: Brachyura: Cyclodorripoida), Records of the Australian Museum 71 (2), pp. 33-69 : 40-42

Cymonomus bathamae Dell, 1971

Figs 6 , 7

Cymonomus bathamae Dell, 1971: 56–59 , figs 1–10.—Wear & Batham, 1975: 113, figs 1–8.— Chapman, 1977: 341, figs 1–10.— Tavares, 1993b: 258.— Ahyong & Brown, 2003: 1373.— Ng et al., 2008: 32.— Webber et al., 2010: 225.—Yaldwyn & Webber, 2011: 227.

Holotype: NMNZ Cr 1867, male (cl 4.6 mm, pcl 3.8 mm, cw 4.0 mm), Papanui Canyon, Otago, New Zealand, 45°51'S 170°02'E, 732 m, RV Munida stn 67-142, 30 November 1967 . Paratypes (all New Zealand): NIWA 68007 , 1 female (cl 3.8 mm, pcl 3.1 mm, cw 3.5 mm), Chatham Rise , 44°05.99'S 179°25.00'E, 344 m , NZOI stn G184, 18 January 1968 ; NMNZ Cr 1868, 1 ovigerous female (cl 5.0 mm, pcl 4.5 mm, cw 5.3 mm), Karitane Canyon, Otago, 45°38'S 171°08'E, 540–720 m , RV Munida stn 68-27, 8 May 1968 ; NIWA 68021 , 1 ovigerous female (cl 4.4 mm, pcl 3.7 mm, cw 4.1 mm), off Otago, 46°18.5'S 170°34.5'E, 680 m , NZOI stn G696, 21 January 1970 .

Other material examined. Chatham Rise, New Zealand: NIWA 31653 , 1 male (cl 4.1 mm, pcl 3.3 mm, cw 3.5 mm), 44° 12.260 –12.750 ' S 178° 55.560 –55.398 'E, 470–479 m, TAN0705/88 , RV Tangaroa , 9 April 2007 .

Description. Carapace quadrate, almost square, lateral margins weakly divergent posteriorly; regions weakly indicated, cervical groove weakly indicated; lower pterygostomian region swollen; anterior and anterolateral surfaces with few long, fine setae, other surfaces sparsely setose. Anterolateral spine prominent, inclined laterally; similar spine on lateral margin behind anterolateral spine. Anterior carapace margin mesial to the anterolateral spine sloping posteriorly towards midline, with short spinules, acute granules. Dorsal and lateral surfaces densely covered with minute granules and spinules anteriorly, spinules longest anterolaterally. Fronto-orbital margin (excluding rostrum and lateral projections) advanced beyond anterolateral margins; 0.6 anterior carapace width; outer orbital processes sharply triangular, elongate, divergent, directed anterolaterally, situated below plane of rostrum, dorsally and laterally spinulate, apex acute, shorter than rostrum. Rostrum length about two-thirds length of eyestalks; 0.11–0.22 pcl; slender, sharply triangular, spinose dorsally and laterally.

Eyestalks strongly divergent (about 30° to median axis), margins subparallel for most of length, ventrally flattened, fused to carapace below rostral base but demarcation distinct; reaching anteriorly slightly beyond antennular peduncle article 1; dorsal surface acutely granulate, lateral and mesial margins spinulate; cornea apparently vestigial, not pigmented.

Epistome with granulate median tubercle and small tubercle mesial to base of antennule; with slender bifid or trifid spine mesial to base of antenna.

Antennular peduncle 0.75–0.76 pcl (male), 0.65–0.70 pcl (female); articles 1 and 2 minutely granulate; article 3 smooth. Antennal articles 1–4 granulate or spinose; article 5 smooth.

Maxilliped 3 ischiobasis subquadrate, surface and margins sparsely granulate, with few acute granules or short spines; shallow longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus slightly shorter than ischium; length 2.2 × width (excluding spines); tapering distally to rounded apex; surface and margins spinulate. Dactylus unarmed. Propodus and carpus spinulate. Exopod unarmed, distally overreaching endopod merus.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose, almost glabrous. Merus finely granulate, with few short, scattered spines. Carpus acutely granulate and spinose, dorsal spines longest. Propodus palm surfaces granulate; dorsal and ventral margins spinose, extending onto pollex. Dactylus longer than dorsal palm length; dorsal margin spinose; outer surface with faint longitudinal carina, occlusal surfaces of dactylus and pollex irregularly crenulate, without gape when fingers closed.

Pereopods 2 and 3, sparsely setose, flexor and extensor margins granulate and spinose, other surfaces granulate; longest spines on extensor margins and dorsal surfaces of propodus and carpus; merus extensor and flexor margins with short spines; dactylus broadly curved, sparsely and minutely spinose proximally, otherwise smooth, without distinct longitudinal rib. Pereopod 3 longest, merus shorter than carapace, 0.91–0.93 pcl (males), 0.87–0.91 pcl (females); dactylus slightly shorter than combined length of propodus and carpus.

Pereopods 4 and 5 finely granulate, sparsely spinose; longer than pereopod 3 merus in both sexes; propodus distoextensor margin unarmed; dactylus markedly shorter than propodus, falcate, with corneous apex and 3 obliquely inclined, corneous spines on flexor margin. Pereopod 5 merus, when folded against carapace, reaching anterior 1/4 of carapace.

Thoracic sternite 3 pentagonal, width 1.8 × length; lateral margins slightly divergent posteriorly to subparallel; surface very sparsely granulate. Margins of sternites 4 and 5 granulate.

Abdomen granulate and minutely spinose, most prominent on somites 2 and 3, very sparsely ornamented on somites 4 and 5. Pleotelson without trace of demarcation between somite 6 and telson; subtriangular, sparsely granulate or minutely spinose; margins straight to slightly convex; apex rounded; width 1.4 × length (male), 1.9 (female).

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.

Egg diameter 0.92 mm.

Remarks. Within the C. bathamae group, C. bathamae is most similar to C. espinosus , C. confinis , and C. brevis , all of which have basally fused, immovable eyes. Cymonomus bathamae is readily distinguished from C. espinosus by the densely granulate carapace surface ( Fig. 6A ) (versus largely smooth, with a few patches of spinules or granules; Fig. 18A ) and from C. confinis by the longer pereopod 5 ( Fig. 8A ) (merus reaching anteriorly to the anterior one-third [ Dell, 1971: fig. 4] rather than midlength of the carapace; Fig. 12A ) and longer maxilliped 3 exopod ( Fig. 8E ) (distinctly overreaching the merus versus reaching to the distal threefourths; Fig 12E ). Distinctions between C. bathamae and C. brevis are outlined under the account of the latter.

Unlike other congeners, sexual dimorphism in the length of the walking legs in C. bathamae is very slight; the proportional pereopod 3 length differs by only 4–5% between the sexes compared to 10–30% in other species. Dell (1971) reported ovigerous females with up to 23 eggs, to 1.4 mm diameter. Development in C. bathamae is abbreviated, with one (possibly two) zoeal stages prior to the megalopa (Wear & Batham, 1975). This reduced developmental staging limits dispersal capabilities and is consistent with the small known range of the species. The eyes of C. bathamae are degenerate, lacking corneal facets, although photoreceptors remain, permitting light detection without image formation ( Chapman, 1977).

Distribution. Southeastern New Zealand, from the Chatham Rise to Otago ( Fig. 7 ); 344– 732 m.

Figures

Figure 6. Cymonomus bathamae Dell, 1971. (A–F) spent female paratype, cl 3.9 mm, pcl 3.3 mm, cw 3.6 mm, Chatham Rise, New Zealand, NIWA 68007. (G–I) male, cl 6.0 mm, pcl 3.3 mm, cw 3.5 mm, Chatham Rise, New Zealand, NIWA 31653. (J) ovigerous female paratype, cl 4.4 mm, pcl 3.7 mm, cw 4.1 mm, off Otago, New Zealand, NIWA 68021. (A) dorsal habitus; (B) posterior abdomen; (C, J) right epistomial spine mesial to base of antenna; (D) fronto-orbital region; (E) right maxilliped 3; (F) thoracic sternite 3; (G) right G1, abdominal view; (H) right G2, abdominal view; (I) pleotelson. Scale:A–B = 2.0 mm; C, J = 0.5 mm; D–I = 1.0 mm.

Figure 7. Cymonomus bathamae Dell, 1971, distribution.

Figure 8. Cymonomus brevis sp.nov., female holotype, cl 3.9 mm, pcl 2.8 mm, cw 3.3 mm, Bay of Plenty, New Zealand, NIWA 76191. (A) dorsal habitus; (B) posterior abdomen; (C) right epistomial spine mesial to base of antenna; (D) fronto-orbital region; (E) right maxilliped 3; (F) thoracic sternite 3. Scale: A–B = 1.0 mm; C = 0.25 mm; C–F = 0.5 mm.

Figure 12. Cymonomus confinis sp. nov., male holotype, cl 3.2 mm, pcl 2.7 mm, cw 2.9 mm, Great Australian Bight, South Australia, NMV J52177. (A) dorsal habitus; (B) abdomen; (C) right epistomial spine mesial to base of antenna; (D) fronto-orbital region; (E) right maxilliped 3; (F) thoracic sternite 3; (G) left G1, abdominal view; (H) left G2, abdominal view. Scale:A–B = 1.0; C–H = 0.5 mm.

Figure 18. Cymonomus espinosus sp. nov. (A–F) female holotype, off Two Rocks, Western Australia, cl 3.9 mm, pcl 3.4 mm, cw 3.5 mm, NMV J55982; (G–I) female paratype, cl 4.1 mm, pcl 3.6 mm, cw 3.7 mm, SE Victoria, NMV J52178; (J–M) female paratype, cl 4.4 mm, pcl 3.8 mm, cw 4.2 mm, Tasmania, NMV J58198. (A) dorsal habitus; (B) posterior abdomen; (C, I, M) left epistomial lobe mesial to base of antenna; (D, G, J) anterior carapace; (E) left maxilliped 3; (F, L) thoracic sternite 3; (G) fronto-orbital region; (H, K) pleotelson. Scale:A, B, G = 2.0 mm; C, I, M = 0.5 mm; D–F, G, H, J–L = 1.0 mm.