Cymonomus clarki Ahyong 2008
Creators: name: Ahyong, Shane T.
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Cymonomidae
Cymonomus
Cymonomus clarki

description: Cymonomus clarki Ahyong, 2008
Figs 10, 11, 30B
Cymonomus clarki Ahyong, 2008: 13–14, fig. 2D, 6.— Webber et al., 2010: 225.—Yaldwyn & Webber, 2011: 227.
Cymonomus soela.— Clark et al., 2010: app. 1. [Not C. soela Ahyong & Brown, 2003]
Holotype: NIWA 29666, ovigerous female (cl 6.9 mm, pcl 5.9 mm, cw 6.6 mm), Graveyard Seamount, Chatham Rise, New Zealand, 42°45.91'S 179°59.26'W, 993–1090 m, coral rubble and rocks, TAN0604/16, RV Tangaroa, 29 May 2006. Paratypes (all New Zealand): NIWA 34965, 1 ovigerous female (cl 7.3 mm, pcl 6.4 mm, cw 7.1 mm), Ritchie Hill, Hawkes Bay, 39°29.44–28.51' S 178°25.05 –25.48'E, 980–1000 m, KAH9907/37, 3 June 1999; NIWA 29663, 1 ovigerous female (cl 6.7 mm, pcl 5.9 mm, cw 6.6 mm), Ghoul Seamount, Chatham Rise, 42°47.85'S 179°59.26'E, 925–1054 m, coral rubble and rocks, TAN0604/118, RV Tangaroa, 7 June 2006.
Other material examined (all New Zealand). Bay of Plenty: NIWA 83182, 1 ovigerous female (cl 6.8 mm, pcl 5.7 mm, cw 6.3 mm), 37°31.72'S 177°17.82'E, 1190–1207 m, seamount sled, TAN1206/146, RV Tangaroa, 28 April 2012; NIWA 83183, 1 ovigerous female (cl 6.9 mm, pcl 5.8 mm, cw 6.4 mm), TAN1206/146.
Chatham Rise: NIWA 64202, 1 female (cl 8.4 mm, pcl 7.0 mm, cw 7.7 mm), 41°53.77–54.22' S 174°55.63 –55.80'E, 913–948 m, TAN1004/134, RV Tangaroa, 27 April 2010; NIWA 24563, 1 ovigerous female (cl 6.3 mm, pcl 5.2 mm, cw 5.7 mm), 42°29.220'S 179°35.406'E, 975 m, beam trawl, TAN1208/57, RV Tangaroa, 24 June 2012; NIWA 53429, 1 ovigerous female (cl 6.3 mm, pcl 5.3 mm, cw 5.9 mm), 42°46.34–46.61' S 179°53.91 –54.08'E, 1073–1100 m, TAN0905/68, RV Tangaroa, 22 June 2009; NIWA 31675, 2 ovigerous females (cl 6.8 mm, pcl 6.0 mm, cw 6.5 mm; cl 7.2 mm, pcl 6.2 mm, cw 6.4 mm), 1 spent female (cl 7.1 mm, pcl 6.2 mm, cw 6.7 mm), 42°47.23–47.16' S 176°42.66 –43.32'W, 996–1009 m, TAN0705/163, RV Tangaroa, 16 April 2007; NIWA 87220, 1 male (cl 5.1 mm, pcl 4.1 mm, cw 4.2 mm), 1 ovigerous female (cl 7.8 mm, pcl 6.8 mm, cw 7.1 mm), 42°48.40–48.78' S 179°49.59 –49.13'E, 1002–1005 m, TAN1208/58, RV Tangaroa, 24 June 2012.
Otago: NIWA 96702, 1 juvenile male (damaged, cl 4.0 mm, pcl 3.3 mm), E of Karitane, 45°38.46'S 171°30.60'E, 1117 m, box core, TAN1310 Caraval FF 2, RV Tangaroa, coll. Anadarko Petroleum Corporation, 2013.
Description. Carapace quadrate, almost square, lateral margins subparallel; regions indistinct; cervical groove indistinct, slightly more pronounced in males than females; lower pterygostomian region swollen; anterior and anterolateral surfaces with long, fine, wiry setae, other surfaces with short fine setae. Anterolateral spine prominent, slender conical, directed anteriorly; 1 or 2 smaller spines on lateral margin behind anterolateral spine. Dorsal and lateral surfaces entirely covered with minute rounded granules, with granules becoming slightly larger and more elongate anterolaterally, bluntly conical, not globose. Fronto-orbital margin (excluding rostrum and outer-orbital processes) at most slightly advanced beyond anterolateral margins; 0.6 anterior carapace width; outer orbital processes slender, elongate, directed anteriorly, situated below plane of rostrum, laterally spinulate, with acute apices, as long as or slight shorter than rostrum. Rostrum about half-length of eyestalks or slightly less; 0.13–0.27 pcl; slender, tapering to acute apex, minutely granulate dorsally and laterally.
Eyestalks divergent (25–30° from median axis), gently tapering, slender, flattened, minutely granulate dorsally, margins acutely granulate, fused to carapace below rostral base but demarcation distinct, reaching anteriorly to end of antennular peduncle article 1; cornea apparently vestigial, not pigmented.
Epistome with small cluster of granules at base of rostrum and blunt tubercle mesial to base of antennules, otherwise smooth; small spine mesial to base of antenna.
Antennular peduncle 1.16 pcl (male) (0.86 juvenile male), 0.72–0.85 pcl (female); articles 1 and 2 minutely granulate; article 3 smooth. Antennal articles irregularly granulate.
Maxilliped 3 ischiobasis subquadrate, sparsely granulate; longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus slightly longer than ischium, length about 2.5 × width, tapering distally to rounded apex; surface and margins with short, slender spines. Dactylus unarmed; propodus and carpus sparsely spinulate. Exopod granulate, reaching beyond carpo-meral articulation but not reaching end of merus of endopod.
Chelipeds (pereopod 1) equal in size and ornamentation, distinctly setose. Merus finely granulate. Carpus granulate, dorsal margin with slender spines. Palm surfaces with fine granules and few scattered acute granules, more prominent on dorsal margin but none produced to spines. Dactylus longer than dorsal palm length; proximal half with scattered granules; with faint longitudinal carina on outer surface, occlusal surfaces of dactylus and pollex crenulate, with slight gape when fingers closed.
Pereopods 2 and 3 distinctly setose; all articles except for dactylus finely granulate; dactylus broadly curved, smooth, with longitudinal rib. Pereopod 3 longest, merus 1.35 pcl (male) (1.13 juvenile male), 1.03–1.08 (female); dactylus slightly shorter than combined length of propodus and carpus.
Pereopods 4 and 5 granulate, setose; longer than pereopod 3 merus in both sexes; propodus distoextensor margin unarmed; dactylus markedly shorter than propodus, falcate, with corneous apex and 4–6 obliquely inclined, corneous spines on flexor margin. Pereopod 5 merus, when folded against carapace, reaching anterior 1/4 of carapace.
Thoracic sternite 3 pentagonal, about 1.5 × wider than long; lateral margins divergent posteriorly; surface sparsely granulate. Margins of sternites 4 and 5 granulate.
Abdomen surface finely granulate. Pleotelson without trace of demarcation between somite 6 and telson; in juveniles males, narrowly triangular; in adult males, broadly subpentagonal, distolateral margin straight, apex obtuse, bluntly angular, width twice length; in females, broadly triangular, distolateral margin concave, apex obtuse rounded, width 1.8–1.9 × length.
Gonopod 1 distal article cannulate, forming copulatory tube, with moderately long distal setae. Gonopod 2 with articles fused; distomesial margin slightly hollowed, apex acute.
Egg diameter 1.20–1.49 mm.
Remarks. Cymonomus clarki, a member of the C. soela group, most closely resembles C. menziesi, from Peru and Chile, in the proportionally elongate pereopod 5, in which the merus reaches to the anterior one-third of the carapace (Fig. 10A) (versus merus not reaching beyond the carapace midlength). Cymonomus menziesi, however, lacks the setose anterolateral carapace margins of C. clarki and has more strongly divergent eyestalks — about 30° from the midline in C. clarki (Fig. 10A, D, M) versus about 45° in C. menziesi (see Garth & Haig, 1971: pl. 1; Guzman, 2003: fig. 1). Overall, C. clarki appears to be the most setose member of the C. soela group, having long, fine setae over the surface of the chelipeds and walking legs (Fig. 10A) (versus very sparse setae in other members of the group). Of the regional species of the C. soela group, C. clarki is most similar to C. dianae, sharing similarly slender eyestalks and setose anterolateral carapace margins (Figs 10D, 16D) (versus comparatively thick eyestalks and almost glabrous anterolateral carapace margins in C. soela and C. tesseris; Fig. 24A, 26D). The granulose (Fig. 10A) rather than nearly smooth (Fig. 16A) outer surface of the cheliped palm will separate C. clarki from C. dianae.
Specimens of C. clarki are largely uniform. The margins of the female pleotelson are usually distinctly concave (Fig. 10B, L), occasionally only weakly concave (Fig. 10K), and the fronto-orbital margin may be slightly advanced ahead of the anterolateral margins (Fig. 10M). As in other congeners, the walking legs and antennular peduncle of C. clarki are proportionally longer in males. The juvenile male substantially resembles the adult male, differing in aspects related to its immaturity: incompletely developed gonopods, a proportionally narrower, more triangular pleotelson (Fig. 10J), and proportionally shorter antennular peduncles and walking legs than in the adult male (0.86 vs 1.16; 1.13 vs 1.35). All females examined are mature; the smallest female (NIWA 24563) is ovigerous. Of the two males examined (NIWA 87220, pcl 4.1 mm; NIWA 96702, pcl 3.3 mm), the smaller is a juvenile, suggesting that males become mature near 4 mm pcl.
Cymonomus clarki is the most widely distributed species of the genus in New Zealand, ranging from the Bay of Plenty south to Otago. It was collected together with the atelecyclid crab, Trichopeltarion janetae Ahyong, 2008, on Ghoul Seamount, Chatham Rise (Ahyong 2008).
Distribution. Eastern New Zealand, from seamounts on the southern Kermadec Ridge (Bay of Plenty), northern Chatham Rise, and off Otago (Fig. 11); 913–1207 m.
description: Published as part of Ahyong, Shane T., 2019, The Cymonomid Crabs of New Zealand and Australia (Crustacea: Brachyura: Cyclodorripoida), pp. 33-69 in Records of the Australian Museum 71 (2) on pages 44-46, DOI: 10.3853/j.2201-4349.71.2019.1682, http://zenodo.org/record/3838013