Cymonomus espinosus, 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 : 53-55

Cymonomus espinosus sp. nov.

http://zoobank.org/NomenclaturalActs/ FF2E3D31-7DC9-426D-B6D7-3F7F47461BFD

Figs 18 , 19

Holotype: NMV J55982 , ovigerous female (cl 3.9 mm, pcl 3.4 mm, cw 3.5 mm), off Two Rocks , Western Australia, Australia, 31°37.08–37.38' S 114°58.32 – 115°14.65'E, 364–404 m, beam trawl, SS10/2005/004, RV Southern Surveyor, coll. R. Wilson, 19 November 2005 . Paratypes: NMV J52178 , 2 ovigerous females (cl 4.1 mm, pcl 3.6 mm, cw 3.7 mm; cl 4.0 mm, pcl 3.6 mm, cw 3.7 mm), SE Victoria, Australia, 38°09.80'S 149°41.71'E, 260–265 m, epibenthic sled, SS01/00/199 , RV Southern Surveyor , 22 April 2000 ; NMV J58198 , 1 spent female (cl 4.4, pcl 3.8 mm, cw 4.2 mm), Huon 400 site, S of Tasmania, Australia, 43°59.50–59.70' S 147°32.77 –33.80'E, 370–410 m, epibenthic (Sherman) sled, SS02/2007/06 , RV Southern Surveyor , coll. T. O’Hara & T. Costa , 31 March 2007 .

Description. Carapace quadrate, almost square, lateral margins subparallel; regions weakly indicated, cervical groove weakly indicated; lower pterygostomian region swollen; anterior and anterolateral surfaces sparsely setose. Anterolateral spine prominent, conical, directed anteriorly; similar spine on lateral margin behind anterolateral spine, followed by several smaller, well-spaced spines or acute granules. Anterior carapace margin mesial to the anterolateral spines sloping posteriorly towards midline, with spinules, acute granules. Dorsal and surface very sparsely ornamented: gastric region with transverse field of spinules in approximately W-shaped pattern; cardiac, intestinal and branchial regions each with field of widely spaced granules. Fronto-orbital margin (excluding rostrum and lateral projections) advanced beyond anterolateral margins; about 0.6 anterior carapace width; outer orbital processes sharply triangular, elongate, divergent, directed anterolaterally, situated below plane of rostrum, dorsally and laterally strongly spinulate, apex acute, shorter than rostrum. Rostrum length exceeding three-fourths length of eyestalks; 0.12–0.16 pcl; slender, sharply triangular, sparsely spinular dorsally and laterally, slightly inclined ventrally.

Eyestalks divergent (23–30° to median axis), margins subparallel for most of length, ventrally flattened, fused to carapace below rostral base but demarcation distinct; reaching anteriorly slightly beyond end of antennular peduncle article 1; dorsal surface sparsely spinulate, lateral and mesial margins spinose, most pronounced and numerous mesially; cornea apparently vestigial, not pigmented.

Epistome with tubercle mesial to base of antennule, otherwise smooth; multidentate lobe mesial to base of antenna, anteriormost largest, prominent, followed by 2 or 3 smaller spines or blunt projections.

Antennular peduncle 0.72–0.83 pcl (female); article smooth or minutely granulate. Antennal article 1 granulate; articles 2–4 spinose or granulate; article 5 smooth.

Maxilliped 3 ischiobasis subquadrate, surface sparsely granulate, distolateral margin spinose; shallow longitudinal median groove; ischium and basis demarcated by faint groove. Merus slightly shorter than ischium; length 2.2 × width (excluding spines); tapering distally to rounded apex; surface and margins spinulate. Dactylus, propodus and carpus spinulate. Exopod sparsely granulate, spinulate, distally overreaching endopod merus.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus finely and sparsely granulate, with few small sines distally. Carpus sparsely granulate; distally and dorsally spinose. Propodus palm surfaces sparsely spinulate and granulate, longest spines along dorsal margin; ventral margin irregularly spinose, not extending onto pollex. Dactylus slightly longer than dorsal palm length; proximal half spinose; outer surface with faint longitudinal carina, occlusal surfaces of dactylus and pollex irregularly crenulate, with slight gape when fingers closed.

Pereopods 2 and 3, sparsely setose, flexor and extensor margins variously spinose, other surfaces sparsely granulate; longest spines on extensor margin of carpus; merus extensor margin with distal spines, otherwise unarmed, flexor margin spinose on proximal half; dactyli broadly curved, unarmed, with longitudinal rib. Pereopod 3 longest, merus 0.86 pcl (female);dactylus shorter than combined length of propodus and carpus.

Pereopods 4 and 5 finely and sparsely granulate, few spines; longer than pereopod 3 merus (female); propodus distoextensor margin unarmed; dactylus markedly shorter than propodus, falcate, with corneous apex and 2 or 3 (usually 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 2.0–2.1 × length; proximal lateral margins slightly divergent posteriorly to subparallel; surface sparsely granulate. Margins of sternites 4 and 5 granulate.

Abdomen granulate and minutely spinose, most prominent on somites 2 and 3, very sparsely ornamented on somites 4 and 5. Pleotelson subtriangular, without trace of demarcation between somite 6 and telson; sparsely granulate; apex bluntly obtuse; width 2.0–2.3 × length.

Egg diameter 1.08 mm; up to 13 eggs carried.

Etymology. Derived from the Latin adjective, espinosus , alluding to the minimal spination or ornamentation on the carapace.

Remarks. Cymonomus espinosus is distinctive in the genus for its minimal carapace granulation and spination, having groups of widely spaced granules or spinules, but otherwise being smooth ( Fig. 18A ). Except for C. mariveneae Ahyong & Ng, 2009 , from the Philippines, the carapace in all other species of the genus is granulate or spinose over the entire surface. Cymonomus mariveneae , however, is readily distinguished from C. espinosus by its possession of globular stalked tubercles ( Ahyong & Ng, 2007: fig. 6A), rather than simple granules or spinules on the carapace margins and pereopods ( Fig. 18A ).

Cymonomus espinosus belongs to the C. bathamae group (see account of C. bathamae ) of which it closely resembles C. bathamae Dell, 1971 , C. brevis sp. nov., and C. confinis sp. nov., sharing the combination of fixed, distinctly divergent eyestalks and having the anterior carapace margin mesial to the anterolateral spines sloping posteriorly inwards. Aside from the minimal carapace spination, C. espinosus differs from C. brevis sp. nov., C. confinis sp. nov. and C. bathamae Dell, 1971 , in its markedly less spinose pereopods 2 and 3 extensor margins, especially on the propodus, being weakly serrate rather than having a row of distinct spines (Fig, 18A); C. espinosus differs from C. confinis in the longer maxilliped 3 exopod, which distinctly overreaches the merus ( Fig. 18E ) (versus three-fourths the merus length in C. confinis ; Fig. 12E ), and the minimal ornamentation of the cheliped palm ( Fig. 18A ) (strongly spinose in C. confinis ; Fig. 12A ).

The examined specimens are mature females, the smallest (holotype, pcl 3.4 mm) being ovigerous. The paratypes of C. espinosus , both from southeastern Australia, have more pronounced eye and anterior carapace spines ( Fig. 18G, J ) than the holotype from southwestern Australia ( Fig. 18A, D ). These differences might reflect the wide geographic separation, but might also be allometric effects given smaller size of the holotype. Unfortunately , the walking legs are intact only in the holotype. The pleotelson width is usually twice the length (Fig, 18B, K) but proportionally wider in one specimen from off Victoria (width 2.3 × length, ovigerous female, pcl 3.6 mm, NMV J52178 ; Fig. 18H ). Variation is also evident in the armature of the multidentate mesial lobe at the base of the antennular articulation: one distinct anterior spine is always present, followed by two (paratypes) or three projections (holotype), variously developed spines or low denticles ( Fig. 18C, I, M ) .

Distribution. Southern Australia from Victoria, Tasmania and Western Australia ( Fig. 19 ); 260– 410 m.

Figures

Figure 12. Cymonomus confinis sp. nov., male holotype, cl 3.2 mm, pcl 2.7 mm, cw 2.9 mm, Great Australian Bight, South Australia, NMV J52177. (A) dorsal habitus; (B) abdomen; (C) right epistomial spine mesial to base of antenna; (D) fronto-orbital region; (E) right maxilliped 3; (F) thoracic sternite 3; (G) left G1, abdominal view; (H) left G2, abdominal view. Scale:A–B = 1.0; C–H = 0.5 mm.

Figure 18. Cymonomus espinosus sp. nov. (A–F) female holotype, off Two Rocks, Western Australia, cl 3.9 mm, pcl 3.4 mm, cw 3.5 mm, NMV J55982; (G–I) female paratype, cl 4.1 mm, pcl 3.6 mm, cw 3.7 mm, SE Victoria, NMV J52178; (J–M) female paratype, cl 4.4 mm, pcl 3.8 mm, cw 4.2 mm, Tasmania, NMV J58198. (A) dorsal habitus; (B) posterior abdomen; (C, I, M) left epistomial lobe mesial to base of antenna; (D, G, J) anterior carapace; (E) left maxilliped 3; (F, L) thoracic sternite 3; (G) fronto-orbital region; (H, K) pleotelson. Scale:A, B, G = 2.0 mm; C, I, M = 0.5 mm; D–F, G, H, J–L = 1.0 mm.

Figure 19. Cymonomus espinosus sp. nov., distribution.