Cymonomus delli Griffin & Brown, 1976

Figs 14, 15, 30C

Cymonomus delli Griffin & Brown, 1976: 251–252, figs 4, 5 [type locality: off Sydney, Australia].— Tavares, 1993a: 141; 1993b: 258.— Poore, 2004: 318, fig. 93c.— MacIntosh et al., 2018: 15.

Cymonomoides delli.— Ahyong & Brown, 2003: 1372.— Ng et al., 2008: 32.

Cymonomus andamanicus.— Poore et al., 2008: 36.— McEnnulty et al., 2011: app. 1. [Not C. andamanicus Alcock, 1905].

Cymonomus sp. 1.— Currie & Sorokin, 2011: app. 1.

Holotype: AM P19379, female (cl 8.6 mm, pcl 7.9 mm, cw 8.3 mm), off Sydney, New South Wales, Australia, 33°51–45' S 151°51 –55'E, 675 m, trawl, FRV Kapala, 19 October 1972.

Other material examined. South Australia: SAM C7657, 1 ovigerous female (cl 8.5 mm, pcl 7.6 mm, cw 8.3 mm), Great Australian Bight, 33°27.096'S 130°41.190'E, 500 m, trawl, SS010 _ T02 BPZ-500, RV Southern Surveyor, coll. D. Currie, 15 August 2010; AM P102703, 2 males (cl 5.9 mm, pcl 5.3 mm, cw 5.3 mm to cl 6.2 mm, pcl 5.5 mm, cw 5.4 mm), 3 ovigerous females (cl 7.8 mm, pcl 7.2 mm, cw 7.8 mm to cl 8.2 mm, pcl 7.5 mm, cw 7.9 mm), 2 females (cl 7.6 mm, pcl 6.6 mm, cw 7.1 mm to cl 7.9 mm, pcl 7.0 mm, cw 7.7 mm; both with rhizocephalan parasite), 33° 29.286 – 29.544 ' S 131°04.44 –03.72'E, 373.6–391.6 m, beam trawl, IN2015_C02_186_135 & 136, RV Investigator, 7 December 2015; AM P103089, 1 male (cl 6.4 mm, pcl 5.7 mm, cw 5.7 mm), 2 ovigerous females (cl 7.3 mm, pcl 6.5 mm, cw 7.1 mm to cl 8.0 mm, pcl 7.2 mm, cw 7.9 mm), 35° 02.568 – 02.268 ' S 134° 04.740 –03.960 'E, 366.8–409.4 m, beam trawl, IN2015_C02_126_127, RV Investigator, 4 December 2015; SAM C12920, 1 ovigerous female (cl 8.2 mm, pcl 7.2 mm, cw 8.0 mm), 33° 22.866 –22.998 ' S 130°15.360 –15.06'E, 420.7–430.6 m, beam trawl, IN2015_C02_389_142, RV Investigator, 15 December 2015.

Western Australia: NMV J53919, 1 ovigerous female (cl 9.0 mm, pcl 8.2 mm, cw 8.9 mm), Jurien Bay, 29°50.52– 51.02' S 114°21.72 –22.02'E, 408–427 m, SS10/2005 080, RV Southern Surveyor, coll. G. Poore, 1 May 2006.

Description. Carapace quadrate, almost square, lateral margins subparallel; regions weakly indicated; lower pterygostomian region swollen; surfaces sparsely setose; carapace slightly more inflated in females than males. Anterolateral spine short, conical; with 1 or 2 small anteriorly directed spines on lateral margin behind anterolateral spine. Dorsal and lateral surfaces entirely covered with minute granules, granules becoming larger and more elongate anterolaterally. Fronto-orbital margin (excluding rostrum and lateral projections) advanced slightly beyond anterolateral margins; 0.5–0.6 anterior carapace width; outer orbital processes pointed, directed anteriorly, triangular in lateral view, situated below plane of rostrum, laterally with acute granules, small spines, reaching midlength of rostrum. Rostrum small, about half-length of eyestalks; 0.08–0.14 pcl; triangular, apex acute, margins concave, minutely granulate laterally and dorsally.

Eyestalks strongly divergent (about 30° to median axis), flattened, stout, width at midlength exceeding one-third length, fused to carapace below rostral base but demarcated from frontal margin; reaching anteriorly beyond midlength of antennular peduncle article 1; dorsal surface minutely granulate, lateral and mesial margins weakly spinulate; cornea apparently vestigial, not pigmented.

Epistome surface granulate, small tubercle at base of rostrum and tubercle mesial to base of antennule; small spine mesial to base of antenna.

Antennular peduncle 0.90–0.92 pcl (male), 0.68–0.75 pcl (female); articles minutely granulate. Antennal articles 1–4 irregularly granulate or minutely spinular; article 5 minutely granulate.

Maxilliped 3 ischiobasis subquadrate, granulate and minutely spinular distally; longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus shorter than ischium; length twice width, tapering distally to rounded apex; surface and margins spinulate. Dactylus unarmed. Propodus and carpus sparsely spinulate. Exopod surface granulate; apex reaching to or slightly beyond carpo-meral articulation but not reaching beyond end of endopod merus.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus finely granulate, scattered small spines. Carpus finely granulate, dorsal margin with few short spines. Propodus palm surfaces with fine granules and few scattered acute granules, dorsal and ventral margins irregularly spinulate. Dactylus longer than dorsal palm length; proximal dorsal two-thirds with spines and granules; with faint longitudinal carina on outer surface, occlusal surfaces of dactylus and pollex crenulate, without gape when fingers closed.

Pereopods 2 and 3 sparsely setose; all articles finely granulate; propodus, carpus and merus with serrated granules and scattered spinules on extensor margins; dactylus broadly curved, few granules or small spines proximally, with longitudinal rib, though slightly less distinct proximally; setose. Pereopod 3 longest; merus 1.04–1.08 pcl (male), 0.87–0.96 pcl (female); dactylus about as long as combined length of propodus and carpus.

Pereopods 4 and 5 minutely granulate, sparsely 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 one-third of carapace.

Thoracic sternite 3 pentagonal, 1.7–1.8 × wider than long; lateral margins divergent posteriorly, surface granulate. Margins of sternites 4 and 5 granulate.

Abdomen with margins and surface finely granulate or minutely spinulate. Pleotelson without somite 6 and telson clearly demarcated by well-defined transverse groove in both sexes; telson broadly rounded, smaller in males than in females but shape and proportions similar in both sexes, width about twice length.

Gonopod 1 with 3 articles; distal article cannulate, forming copulatory tube, with long distal setae. Gonopod 2 with articles fused, distomesial margin slightly hollowed, apex acute.

Egg diameter 0.93–1.40 mm.

Remarks. Cymonomus delli Griffin & Brown, 1976, long known only from the female holotype collected off Sydney, southeastern Australia, is now known from Tasmania, South Australia and southwest Western Australia as result of several CSIRO expeditions off southern Australia (MacIntosh et al., 2018). Most records of C delli are from the upper slope near the shelf-break (c. 400 m) although it has been recorded to 675 m. Like its congeners, sexual dimorphism in C. delli is evident in the proportionally longer walking legs and antennules of males. All examined specimens appear to be mature, and the smallest recorded female is ovigerous at pcl 6.5 mm. Two specimens of C. delli (AM P 102703) from the Great Australian Bight are infected by rhizocephalan parasites.

Distinctions between species of the C. delli group are primarily morphometric. In C. delli, the fronto-orbital width (as a proportion of the distance between anterolateral carapace spines) is comparatively narrow (0.49–0.58; mean 0.54) relative to other species in the C. delli group (0.58 or greater, usually> 0.60). Within the group, C. delli is closest to C. cognatus from East Asia and C. andamanicus from the Andaman Sea, sharing similar walking leg morphometrics. From C. cognatus, C. delli differs in having proportionally shorter antennules (0.89–0.92 pcl in males and 0.69–0.78 pcl in females versus 0.98–1.00 pcl in males and 0.80–0.88 pcl in females), and a distally wider maxilliped 3 ischiomerus. The portion of the maxilliped 3 ischiomerus distal to the palp articulation is as long as wide in C. delli but longer than wide in C. cognatus.

Cymonomus delli is difficult to distinguish from C. andamanicus, which, unfortunately, is known only from the description and figures of the male holotype (Alcock, 1905; Alcock et al., 1907: pl. 79 figs 2, 2a, b). Cymonomus delli appears to differ from C. andamanicus in the proportionally narrower fronto-orbital width (˂0.60 versus 0.66) and subparallel versus posteriorly divergent lateral carapace margins (cf Alcock et al., 1907: pl. 79 fig. 2a). Accordingly, the previous record of C. andamanicus Alcock, 1905, from southern Western Australia (Poore et al., 2008) corresponds to C. delli. Nevertheless, the currently recognized distinctions between C. andamanicus and C. delli rely on the accuracy of Alcock’s account and figures, and it is conceivable that the two nominal species could be conspecific. A redescription of C. andamanicus is required.

Distribution. Southern Australia, from New South Wales (off Sydney), the Great Australian Bight and Jurien Bay, Western Australia (Fig. 15); 367–675 m, usually about 400 m.