Cymonomus triplex, 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 : 64-66

Cymonomus triplex sp. nov.

http://zoobank. org/NomenclaturalActs/ 16BBF692-671F-4B10-A966-AC188FB30712

Figs 28 , 29 , 30F

Cymonomus sp. MoV 5001.— Poore et al., 2008: 36, unnumbered fig. [part, 2 specimens from 401–539 m].— McEnnulty et al., 2011: 183, unnumbered fig. [part].

Holotype: NMV J53917 , female (cl 4.3 mm, pcl 3.7 mm, cw 4.2 mm), off Point Hillier , Western Australia, Australia, 35°22.90'S 117°12.42'E, 539 m, beam trawl, SS10/2005/019, RV Southern Surveyor, coll. R. Wilson, 22 November 2005 . Paratype: NMV J53918 , female (cl 3.9 mm, pcl 3.4 mm, cw 4.0 mm), Jurien Bay , Western Australia, Australia, 29°52.07–52.43' S 114°23.22 –23.88'E, 401–414, beam trawl, SS10/2005/078 , RV Southern Surveyor , coll. G. Poore, 2 December 2005 .

Other material examined. South Australia: NMV J68440 , 1 ovigerous female (cl 4.0 mm, pcl 4.0 mm, cw 3.5 mm), Great Australian Bight , 35°12.53'S 134°27.05'E, 457 m, beam trawl, SS03/2008/48 , RV Southern Surveyor , 5 March 2008 ; AM P103028 , 1 ovigerous female (cl 3.8 mm, pcl 3.5 mm, 3.7 mm), Great Australian Bight , 35° 02.568 –02.268 ' S 134° 04.740 –03.960 'E, 366.8–409.4 m, beam trawl, IN2015_C02_126_104 , RV Investigator , 4 December 2015 (“ Cymonomus sp. MoV 7327”).

Description. Carapace quadrate, almost square, lateral margins weakly divergent posteriorly; regions weakly indicated, cervical groove weakly indicated; lower pterygostomian region swollen; anterior and lateral surfaces with few long, fine setae, other surfaces sparsely setose. Anterolateral spine prominent, inclined laterally; similar spine on lateral margin behind anterolateral spine, with shorter spinules, acute granules. Anterior carapace margin mesial to the anterolateral spines sloping posteriorly towards midline, with short spinules, acute granules. Dorsal and lateral surfaces covered with minute granules and spinules, spinules longest on anterior half of carapace. Fronto-orbital margin (excluding rostrum and lateral projections) slightly 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, as long rostrum. Rostrum length slightly exceeding halflength of eyestalks; 0.10–0.15 pcl; slender, spiniform, spinose dorsally and laterally; slightly inclined ventrally.

Eyestalks weakly divergent (5–15° from median axis), slender, tapering, ventrally flattened, slightly movable, not fused to carapace; reaching anterior ¾ of antennular peduncle article 1; dorsal surface and margins granulate and sparsely spinose; cornea apparently vestigial, not pigmented. Epistome with compound tubercle at base of rostrum and 2 or 3 small acute tubercles mesial to base of antennule; without spine mesial to base of antenna.

Antennular peduncle 0.80–0.93 pcl (female); articles 1 and 2 minutely granulate; article 3 smooth.Antennal articles granulate or minutely spinular.

Maxilliped 3 ischiobasis subquadrate, surface and margins sparsely granulate, with scattered acute granules or short spines; shallow longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus as long as ischium; length 2.6 × width (excluding spines); tapering distally to rounded apex; surface and margins spinulate. Dactylus unarmed. Propodus and carpus spinulate. Exopod granulate, distally overreaching endopod merus.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus sparsely granulate or minutely spinose. 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; proximal dorsal margin spinose; outer surface with faint longitudinal carina, occlusal surfaces of dactylus and pollex smooth or irregularly crenulate, with slight gape when fingers closed.

Pereopods 2 and 3 sparsely setose, sparsely granulate; propodus and carpus extensor margins acutely granulate and with short spines, flexor margins unarmed; merus extensor and flexor margins acutely granulate and with short spines; dactylus broadly curved, sparsely granulate proximally, otherwise smooth, without distinct longitudinal rib. Pereopod 3 longest, merus 0.94–1.03 pcl (female); dactylus slightly shorter than combined length of propodus and carpus.

Pereopods 4 and 5 finely granulate, sparsely spinose; longer than pereopod 3 merus (female); propodus distoextensor margin unarmed; dactylus markedly shorter than propodus, falcate, with corneous apex and 2 or 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 1.6–1.9 × length; lateral margins weakly to strongly divergent posteriorly; surface sparsely granulate. Margins of sternites 4 and 5 granulate.

Abdomen granulate, 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; margins slightly

concave; apex blunt; width 1.6–1.7 × length (female).

Egg diameter 0.95–1.05 mm.

Etymology. From the Latin, triplex , threefold, as the third

Indo-West Pacific member of the C. bathamae group that

has slightly movable, rather than fixed, eyestalks; used as a

noun in apposition.

Remarks. Cymonomus triplex sp. nov., a member of the C. bathamae group, is most closely allied to C. valdiviae Lankester, 1903 , from East Africa and C. umitakae Takeda, 1981 , from Japan. These three species differ from other members of the C. bathamae group in sharing sharply triangular outer orbital processes that are subequal to rostral length, and weakly divergent, slightly movable eyestalks that are distinctly longer than the rostrum. Cymonomus triplex is readily distinguished from C. umitakae and C. valdiviae in the acutely granulate (with a few small spines) ( Fig. 28A ) rather than prominently spinose extensor margins of the carpus and propodus of pereopods 2 and 3 ( Ahyong, 2014: fig. 14A; Ahyong & Ng, 2017: fig. 6A). A fourth species of the C. bathamae group having slightly movable eyestalks, C. guillei Tavares, 1991 , occurs off Brazil; it differs from the Indo-West Pacific members of the group in the rostrum reaching to, or slightly beyond, the distal end of the eyestalks ( Tavares, 1991; fig. 7B). Poore et al. (2008) and McEnnulty et al. (2011) figured the holotype of C. triplex in colour as “ Cymonomus sp. MoV 5001” ( Fig. 30F ).

Distribution. Great Australian Bight, South Australia, to Jurien Bay, Western Australia ( Fig. 29 ); 367– 539 m.

Figures

Figure 28. Cymonomus triplex sp. nov. (A–F) female holotype, cl 4.3 mm, pcl 3.7 mm, cw 4.2 mm, off Point Hillier, Western Australia, NMV J53917. (G–H) ovigerous female, cl 3.8 mm, pcl 3.5 mm, cw 3.7 mm, Great Australian Bight, South Australia, AM P103028. (A) dorsal habitus; (B) posterior abdomen; (C) right epistomial spine mesial to base of antenna; (D) fronto-orbital region; (E) right maxilliped 3; (F–G) thoracic sternite 3; (H) pleotelson. Scale: A, B, H = 2.0 mm; C = 0.5 mm, D–G = 1.0 mm.

Figure 29. Cymonomus triplex 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).