Cymonomus tesseris, 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 : 62-64

Cymonomus tesseris sp. nov.

http://zoobank.org/NomenclaturalActs/ 7A75D24A-1B1B-4A64-8767-D165D60370E2

Figs 26 , 27

Cymonomus sp. MoV 5001.— Poore et al., 2008: 36 (part, NMV J60743 only).

Holotype: NMV J60743 , male (cl 6.6 mm, pcl 5.7 mm, cw 5.9 mm), Perth Canyon , Western Australia, Australia, 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 of holotype. Carapace quadrate, almost square, lateral margins slightly divergent posteriorly; regions indistinct; cervical groove indistinct; lower pterygostomian region swollen; anterior and anterolateral surfaces with few setae, almost glabrous. Anterolateral spine short, blunt, fusiform, inclined laterally. Dorsal and lateral surfaces entirely covered with minute rounded granules, with granules becoming slightly larger and more elongate anterolaterally, bluntly conical to subglobose. Fronto-orbital margin (excluding rostrum and outer-orbital processes) advanced beyond anterolateral margins; 0.6 anterior carapace width; outer orbital processes stout, elongate, directed anteriorly, situated below plane of rostrum, laterally bluntly spinulate, apex acute, 2/3 rostral length. Rostrum half-length of eyestalks; 0.16 pcl; slender, tapering to acute apex, minutely granulate dorsally and laterally.

Eyestalks divergent (25° from median axis), margins subparallel for most of length, slender, flattened, granulate, granules elongate on mesial margins, fused to carapace below rostral base but demarcation distinct, reaching anteriorly almost to end of antennular peduncle article 1; cornea apparently vestigial, not pigmented.

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

Antennular peduncle 0.92 pcl (male); articles 1 and 2 minutely granulate; article 3 smooth. Antennal articles minutely spinulate.

Maxilliped 3 ischiobasis subquadrate, granulate; longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus as long as ischium, length 2.3 × width, tapering distally to rounded apex; surface and margins with short, blunt 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 granulate. Carpus granulate, dorsal margin with prominent conical spines flanked by shorter blunt spines. Propodus palm surfaces entirely granulate, dorsal and ventral margins with granules and elongate tubercles, extending onto proximal half of pollex. Dactylus longer than dorsal palm length; dorsal margin with short, blunt, slender spines and granules; with faint longitudinal carina on outer surface, occlusal surfaces of dactylus and pollex crenulated, with slight gape when fingers closed.

Pereopods 2 and 3 sparsely setose; all articles except for dactylus granulate; propodus, carpus and merus with coarsely granulate extensor margins; dactylus broadly curved, smooth, with longitudinal rib. Pereopod 3 longest, merus 1.16 pcl (male); dactylus as long as combined length of propodus and carpus.

Pereopods 4 and 5 granulate, unarmed, almost glabrous; shorter than pereopod 3 merus (male); 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 midlength of carapace.

Thoracic sternite 3 pentagonal, 1.7 × wider than long; proximal lateral margins subparallel; 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; distolateral margin straight; apex obtuse, bluntly rounded; width twice length (male).

Gonopod 1 distal article cannulate, forming copulatory tube, with moderately long distal setae. Gonopod 2 with articles fused; distomesial margin slightly hollowed, apex acute.

Etymology. From the Greek, tessera, four, alluding to the new species being the fourth member of the C. soela group from the study area; used as a noun in apposition.

Remarks. Cymonomus tesseris sp. nov. is one of four members of the C. soela group occurring in New Zealand and Australia, of which it is closest to C. soela from southern and eastern Australia. The new species, known only from the Western Australian holotype male, differs from C. soela in its proportionally shorter walking legs and antennules. The male pereopod 3 merus proportions of C. tesseris , at 1.16 pcl, are similar to those of female C. soela (1.00–1.19 pcl) ( Figs 24A , 26A ), and considerably shorter than in male C. soela (1.29–1.47 pcl). Similarly, the proportional length of the male antennules of C. tesseris (0.92 pcl) is within the range of female C. soela (0.78–0.90) and shorter than in male C. soela (1.00–1.10 pcl). Although females of C. tesseris are yet to be collected, they can be expected to have proportionally shorter walking legs and antennules than males, and as such would not approach either sex of C. soela in these features. Cymonomus tesseris was collected together with the similar species, C. dianae sp. nov., but is readily distinguished by the same features that distinguish the latter from C. soela : smaller anterolateral carapace spines ( Fig. 26A ), proportionally thicker eyestalks ( Fig. 26D ), near glabrous versus distinctly setose anterolateral margins of the carapace ( Fig. 26A ), and the distinctly granulate versus near smooth cheliped palms ( Fig. 26A ). Additionally, the pereopod 3 merus is proportionally shorter in C. tesseris than in C. dianae (1.16 pcl vs 1.37–1.47 pcl in males).

Distribution. Presently known only from Perth Canyon, Western Australia ( Fig. 27 ); 848–1050 m.

Figures

Figure 24. Cymonomus soela Ahyong & Brown, 2003. (A–G) female holotype, cl 7.4 mm, pcl 6.3 mm, cw 7.1 mm, off St. Patricks Head, Tasmania, AM P62846. (J–M) male, cl 6.8 mm, pcl 5.7 mm, cw 6.0 mm, Great Australian Bight, South Australia, AM P102902. (A) dorsal habitus; (B) abdomen; (C) right epistomial spine mesial to base of antenna; (D) left maxilliped 3; (E) thoracic sternite 3; (F) left eye, distal portion; (G–H) right P4–5 dactylus; (I) frontal margin; (J) anterior carapace; (K) posterior telson; (L) right G1, abdominal view; (M) right G2, abdominal view. Scale: A–B = 2.0 mm; C, G, H = 0.5 mm; D–F, I, K–M = 1.0 mm. (A, B, D, F–I modified after Ahyong & Brown 2003: figs 3, 4).

Figure 26. Cymonomus tesseris sp. nov., male holotype, cl 6.6 mm, pcl 5.7 mm, cw 5.9 mm, Perth Canyon, Western Australia, NMV J60743. (A) dorsal habitus; (B) posterior abdomen; (C) right epistomial spine mesial to base of antenna; (D) fronto-orbital region; (E) right anterolateral carapace spine; (F) right maxilliped 3; (G) thoracic sternite 3; (H) right G1, abdominal view; (I) right G2, abdominal view. Scale: A–B = 2.0 mm; C = 0.5 mm; D–I = 1.0 mm.

Figure 27. Cymonomus tesseris sp. nov., distribution.