Cymonomus dianae, Ahyong, 2019

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 : 50-53

Cymonomus dianae sp. nov.

http://zoobank.org/NomenclaturalActs/ 5AC1C3A8-6A5D-4272-A3AD-C 120296 D2E60

Figs 16 , 17 , 30D

Cymonomus quadratus valdiviae .— Ihle, 1916: 121–124, fig. 67. [Not C. valdiviae Lankester, 1903 ]

Cymonomus sp. MoV 5001.— Poore et al., 2008: 36 (part).— McEnnulty et al., 2011: app. 1.

Holotype: NMV J58733 , ovigerous female (cl 6.4 mm, pcl 5.3 mm, cw 6.1 mm), Mermaid L 24 transect, Western Australia, Australia, 16°38.06–38.76' S 119°09.21 –08.03'E, 987–990 m, SS05/2007/068, RV Southern Surveyor , 17 June 2007 (Aq.#037, “ Cymonomus sp. MoV5001”) . Paratypes: NMV J58734 , 3 males (cl 5.2 mm, pcl 4.3 mm, cw 4.5 mm to cl 6.0 mm, pcl 5.0 mm, cw 5.4 mm), Leveque L 27 transect, Western Australia, Australia, 14°33.06–33.58' S 121°15.36 –16.58'E, 1021–1023 m, SS05/2007/155 , RV Southern Surveyor , 4 July 2007 (Aq.#035, “ Cymonomus sp. 2”) .

Other material examined. Western Australia: NMV J53916 , 5 males (cl 6.3 mm, pcl 5.3 mm, cw 5.8 mm to cl 6.8 mm, pcl 5.7 mm, cw 6.1 mm), 1 ovigerous female (cl 7.1 mm, pcl 5.8 mm, cw 6.6 mm), 3 spent females (cl 6.7 mm, pcl 5.4 mm, cw 6.4 mm to cl 7.4 mm, pcl 6.1 mm, cw 7.1 mm), Perth Canyon, 31° 58.283 –57.317 ' S 115° 06.000 –06.833 'E, 848–1050 m, beam trawl, SS10/2005/071 , RV Southern Surveyor , coll. R. Wilson, 29 November 2005 .

Description. Carapace quadrate, almost square, lateral margins slightly divergent; regions indistinct, cervical groove deeper, distinctly more pronounced in males than females, broadly V-shaped; lower pterygostomian region swollen; anterior and anterolateral surfaces with long, fine, wiry setae, other surfaces with sparse, 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. Frontoorbital margin (excluding rostrum and outer-orbital processes) advanced beyond anterolateral margins, more pronounced in males than females; 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 halflength of eyestalks; 0.16–0.24 pcl; slender, tapering to acute apex, granulate dorsally and laterally.

Eyestalks divergent (17– 22° from median axis), margins subparallel for most of length, slender, flattened, minutely granulate dorsally, margins acutely granulate, fused to carapace below rostral base but demarcation distinct, extending anteriorly to slightly short of to slightly beyond antennular peduncle article 1; cornea apparently vestigial, not pigmented.

Epistome with cluster of granules at base of rostrum and blunt, elongated compound tubercle mesial to base of antennules, otherwise smooth; small spine mesial to base of antenna.

Antennular peduncle 1.08–1.21 pcl (male), 0.88–0.93 pcl (female); article 1 granular, often with small spines distally; article 2 minutely granulate; article 3 smooth. Antennal articles irregularly granulate, laterally spinular.

Maxilliped 3 ischiobasis subquadrate, sparsely granulate; longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus as long as ischium, length about 2.5 × width, tapering distally to rounded apex; surface and margins with slender spines. Dactylus unarmed; propodus and carpus spinulate. Exopod granulate, reaching beyond carpo-meral articulation but not reaching end of merus of endopod.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus finely granulate, distally sparsely spinulate. Carpus granulate, dorsal margin with slender, allantoid spines. Propodus palm central surface smooth (at most microscopically granulate, granules considerably smaller than granules at periphery), dorsal and ventral margins with distinct granules, conical and allantoid spines. Dactylus longer than dorsal palm length; proximal dorsal half with few small blunt spines; with faint longitudinal carina on outer surface, occlusal surfaces of dactylus and pollex weakly crenulated to smooth, without gape when fingers closed.

Pereopods 2 and 3 sparsely setose; all articles except for dactylus finely granulate; propodus and carpus with bluntly spinular extensor margins; merus with bluntly spinular extensor and flexor margins; dactyli broadly curved, smooth, with longitudinal rib. Pereopod 3 longest, merus 1.37–1.47 pcl (male), 1.16–1.27 (female); dactylus almost as long as combined length of propodus and carpus.

Pereopods 4 and 5 granulate, minutely spinulate, almost glabrous; longer than pereopod 3 merus in both sexes; propodus distoextensor margin unarmed on pereopod 4, with small spine or tubercle on pereopod 5; 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 midlength 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 or minutely spinulate. Pleotelson without trace of demarcation between somite 6 and telson; pentagonal; apex obtuse, bluntly rounded; male pleotelson distolateral margin straight in males, concave in females; width about twice length in both sexes.

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 1.16–1.22 mm.

Etymology. Named after Diane Brown, formerly Australian Museum, for her enthusiastic interest in cymonomid crabs and other decapod crustaceans.

Remarks. Cymonomus dianae sp. nov., a member of the C. soela group, most closely resembles C. deforgesi Ahyong & Ng, 2009 , from the northern hemisphere (South China Sea to Japan; Ahyong & Ng, 2009, 2017), sharing slender, divergent eyestalks and prominent anterolateral spines on the carapace with long “wiry” setae. The new species differs from C. deforgesi in the following features: the cheliped palm surface is smooth or microscopically granular rather than distinctly granulate ( Fig. 16A, J ); the pereopod 3 merus in females is proportionally more elongate (1.16–1.27 pcl versus 1.00–1.09 pcl) and the margins of the female telson are distinctly concave in the distal half ( Fig. 16B ), rather than straight ( Ahyong & Ng, 2017: fig. 4K). Males of both C. dianae and C. deforgesi , however, have similarly elongated walking legs ( Fig. 16A ) (1.36–1.47 pcl versus 1.36–1.41 pcl, respectively).As in C. deforgesi and C. soela , the cervical groove of female C. dianae is less pronounced than in males and the fronto-orbital region less anteriorly “protruding”. Aside from sexual dimorphism, little variation is evident in the present series. In C. dianae , the granulation of the margins of the pereopods 2 and 3 merus is typically pronounced (as in the holotype), though shorter and less distinct in some specimens.

Cymonomus dianae was collected together with C. tesseris in Perth Canyon , southwestern Australia. On the basis of the published account, Ihle’s (1916: fig. 67) “ Cymonomus quadratus valdiviae ”, from Ceram at 835 m, is referred here to C. dianae , extending the range of the species to southern Indonesia. “ Cymonomus sp. MoV 5001”, reported and figured by Poore et al. (2008) (and repeated by McEnnulty et al., 2011), comprises three species: C. dianae sp. nov., C. tesseris sp. nov. and C. triplex sp. nov. (figured).

Distribution. Perth Canyon, southern Western Australia to the North-West Shelf and Ceram, Indonesia ( Fig. 17 ); 848–1050 m.

Figures

Figure 16. (A–F) Cymonomus dianae sp. nov., ovigerous female holotype, cl 6.4 mm, pcl 5.3 mm, cw 6.1 mm, Mermaid L24 transect, Western Australia, NMV J58733. (G–I) Cymonomus dianae sp. nov., male paratype, cl 6.4 mm, pcl 5.4 mm, cw 5.8 mm, Perth Canyon, Western Australia, NMV J53916. (J) Cymonomus deforgesi Ahyong & Ng, 2009, male, cl 6.4 mm, pcl 5.5 mm, cw 6.0 mm, Dongsha Islands, South China Sea, ZRC 2017.0107. (A) dorsal habitus; (B) posterior abdomen; (C) fronto-orbital region; (D) right epistomial spine mesial to base of antenna; (E) right maxilliped 3; (F) thoracic sternite 3; (G) abdominal somite 5 and pleotelson; (H) right G1, abdominal view; (I) right G2, abdominal view; (J) right chela. Scale: A–B, J = 2.0 mm; C = 0.5 mm; D–I = 1.0 mm.

Figure 17. Cymonomus dianae sp. nov., distribution.

Figure 30. (A) Cymonomus alius sp. nov., male paratype, pcl 4.7 mm, cw 4.8 mm, Chatham Rise, New Zealand, TAN0705/24, NIWA 31642; (B) C. clarkiAhyong, 2008, ovigerous female paratype,pcl 5.9 mm,cw 6.6 mm,Chatham Rise, New Zealand,TAN0604/118, NIWA 29663; (C) C.delli Griffin & Brown, 1976, ovigerous female, pcl 7.2 mm, cw 7.9 mm, GreatAustralian Bight, SouthAustralia, IN2015_C02- 126-127, AM P103089; (D) C. dianae sp. nov., male, pcl 5.7 mm, cw 6.1 mm, Perth Canyon, Western Australia, SS10/2005/071, NMV J53916; (E) C. soela Ahyong & Brown, 2003, male, pcl 5.7 mm, cw 6.0 mm, Great Australian Bight, South Australia, IN2015-C02-382- 108, AM P102902; (F) C. triplex sp. nov., female holotype, pcl 3.7 mm, cw 4.2 mm, off Point Hillier, Western Australia, SS10/2005/019, NMV J53917; (G–H) C. karenae sp. nov., female holotype, Tasmania, pcl 6.3 mm, cw 6.5 mm, NMV J55663. Photo credits: A–B (C. Marriott, NIWA), C–G (K. Gowlett-Holmes, CSIRO).