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

description: Cymonomus alius sp. nov.
http://zoobank.org/NomenclaturalActs/ 84215778-F073-409A-9732-88D4D3860A68
Figs 4, 5, 30A
Cymonomus aequilonius.— Ahyong, 2008: 12–13, fig. 1F [not C. aequilonius Dell, 1971].
Holotype: NIWA 34966, spent female (cl 7.7 mm, pcl 6.2 mm, cw 6.7 mm), Tims Bank, S of Ritchie Hill, New Zealand, 40°01.26–01.20' S 178°04.15 –04.09'E, 797–804 m, KAH9907/01, RV Kaharooa, 1 June 1999. Paratypes (all New Zealand): NIWA 121121, 1 male (cl. 6.0 mm, pcl 4.5 mm, cw 4. 7 mm), collected with holotype; NIWA 16829, 1 ovigerous female (cl 8.9 mm, pcl 7.1 mm, cw 8.2 mm), Mernoo Bank, Chatham Rise, 44°20.0'S 173°54.2'E, 675 m, S0161, 28 October 1979; NIWA 31642, 1 male (cl 5.9 mm, pcl 4.7 mm, cw 4.8 mm), 44°07.25–07.45' S 178°50.59 –50.69'E, Chatham Rise, 512–513 m, TAN0705/24, RV Tangaroa, 4 April 2007.
Description. Carapace quadrate, almost square, lateral margins subparallel to slightly divergent posteriorly; regions weakly indicated, cervical groove weakly indicated, broadly V-shaped; lower pterygostomian region swollen; anterolateral surfaces with few scattered setae.
Anterolateral spine short, blunt, conical, directed anteriorly; similar spine 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 outerorbital processes) advanced beyond anterolateral margins; 0.6 anterior carapace width; outer orbital processes stout, elongate, directed anteriorly, situated below plane of rostrum, laterally spinulate, apex acute, about half rostral length. Rostrum distinctly longer than eyestalks; 0.25–0.34 pcl; slender, tapering to acute apex, granulate dorsally and laterally.
Eyestalks strongly divergent (about 45° from median axis), stout, flattened, minutely granulate dorsally, acutely granulate and weakly spinulate along mesial margin, fused to carapace below rostral base but demarcation distinct, reaching anteriorly beyond midlength of antennular peduncle article 1; cornea apparently vestigial, not pigmented.
Epistome with tubercle mesial to base of antennules, otherwise smooth; bifid spine mesial to base of antenna.
Antennular peduncle 0.93–1.00 pcl (male), 0.58–0.74 pcl (female); articles 1 and 2 minutely granulate; article 3 smooth. Antennal articles irregularly granulate or minutely spinular.
Maxilliped 3 ischiobasis subquadrate, sparsely granulate and minutely spinular; longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus slightly shorter than ischium; length about twice width, tapering distally to rounded apex; surface and margins spinulate. Dactylus conical, unarmed; propodus and carpus sparsely spinulate. Exopod surface sparsely granulate, distal margin unarmed; apex not reaching beyond end of endopod merus.
Chelipeds (pereopod 1) equal in size and ornamentation, setose. Merus finely granulate. Carpus granulate, dorsal margin with 4 or 5 spines. Propodus palm surfaces granulate; dorsal and ventral margins with few conical spines and tubercles. Dactylus longer than dorsal palm length; proximal dorsal half with few small spines; with faint longitudinal carina on outer surface, occlusal surfaces of dactylus and pollex uneven, without gape when fingers closed.
Pereopods 2 and 3 finely setose; all articles except for dactylus finely granulate; propodus and carpus with minutely spinular extensor margins; merus margins unarmed; dactylus broadly curved, smooth, with weak longitudinal rib. Pereopod 3 longest, merus 1.29–1.37 pcl (male), 1.03–1.05 pcl (female); dactylus slightly shorter than combined length of propodus and carpus.
Pereopods 4 and 5 finely granulate, some minute spines, glabrous; longer than pereopod 3 merus in both sexes; propodus distoextensor margin unarmed; dactylus markedly shorter than propodus, falcate, with corneous apex and 4 obliquely inclined, corneous spines on flexor margin. Pereopod 5 merus, when folded against carapace, reaching anterior one-fifth of carapace.
Thoracic sternite 3 pentagonal, width about twice length; lateral margins divergent posteriorly; surface sparsely granulate. Margins of sternites 4 and 5 weakly granulate.
Abdomen surface finely granulate or minutely spinulate. Pleotelson without trace of demarcation between somite 6 and telson distally obtuse, bluntly rounded, length about half width 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 1.14 mm.
Etymology. From the Latin adjective alius, another, alluding to the similarity of the new species to C. aequilonius.
Remarks. Cymonomus alius sp. nov. is morphologically and geographically nearest to its New Zealand congener, C. aequilonius. Males of C. aequilonius are presently unknown, but females of the two species differ by the proportional lengths of the walking legs and antennular peduncle: pereopod 3 merus in females 1.03–1.05 pcl in C. alius (Fig. 4A), 1.33 pcl in C. aequilonius (Fig. 2A); antennular peduncle 0.58–0.74 pcl in C. alius, 0.83 in C. aequilonius. As such, the proportional lengths of the walking legs of male C. alius resemble those of female C. aequilonius. Apart from sexual dimorphism, the type specimens of C. alius are largely uniform. All have two epistomial spines mesial to the base of the antenna (Fig. 4C), although the posteriormost spine in one male (NIWA 31642) is blunt on one side, broken on the other.
Although based on few records, the known distributions of C. aequilonius and C. alius, respectively, with one species occurring north and the other south of East Cape (c. 37°40'S) (Figs 3, 5), parallel those of another apparent species pair, C. brevis and C. bathamae (Figs 7, 9). The northsouth distributions of these species pairs correspond to the Aupourian and Cookian provinces, respectively, demarcated by the subtropical convergence in the vicinity of the Chatham Rise (Morton, 2004). The holotype of C. alius was collected together with the goneplacid crab, Pycnoplax victoriensis (Rathbun, 1923) (Ahyong 2008).
Distribution. Southeastern New Zealand, from Tims Bank to the Chatham Rise (Fig. 5); 512– 804 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 38-40, DOI: 10.3853/j.2201-4349.71.2019.1682, http://zenodo.org/record/3838013