Cymonomus brevis, 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 : 42-44

Cymonomus brevis sp. nov.

http://zoobank. org/NomenclaturalActs/ 7BCA2CEE-DEE6-4C00-AC5F-82982D41957D

Figs 8 , 9

Holotype: NIWA 76191 , spent female (cl 3.2 mm, pcl 2.7 mm, cw 3.1 mm), Bay of Plenty, New Zealand, 35°47.80'S 175°13.00'E, 151 m, NZOI stn I4, 2 May 1975.

Description of holotype. Carapace quadrate, almost square, lateral margins weakly divergent posteriorly; regions weakly indicated, cervical groove weakly indicated; lower pterygostomian region swollen; anterior and anterolateral surfaces with few long, fine setae, other surfaces sparsely setose. Anterolateral spine prominent, inclined laterally; similar spine on lateral margin behind anterolateral spine. Anterior carapace margin mesial to the anterolateral spines sloping posteriorly towards midline, with minute spinules, acute granules. Dorsal and lateral surfaces sparsely covered with rounded or conical granules. 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 minutely spinulate, apex acute, shorter than rostrum. Rostrum length about three-fourths length of eyestalks; 0.23 pcl; slender, sharply triangular, sparsely granulate dorsally.

Eyestalks strongly divergent (35° to median axis), margins subparallel for most of length, ventrally flattened, fused to carapace below rostral base but demarcation distinct; not reaching anteriorly to end of antennular peduncle article 1; dorsal surface acutely granulate, lateral and mesial margins spinulate; cornea apparently vestigial, not pigmented.

Epistome with acute granule mesial to base of antennule, otherwise smooth; with slender spine mesial to base of antenna.

Antennular peduncle 0.71 pcl (female); articles 1 and 2 minutely granulate; article 3 smooth. Antennal articles granulate or spinose.

Maxilliped 3 ischiobasis subquadrate, surface and margins sparsely granulate, with few acute granules or short spines; shallow longitudinal sublateral groove; ischium and basis demarcated by faint groove. Merus slightly shorter than ischium; length twice width (excluding spines); tapering distally to rounded apex; surface and margins spinulate. Dactylus, propodus and carpus spinulate. Exopod sparsely granulate, distally overreaching endopod merus.

Chelipeds (pereopod 1) equal in size and ornamentation, sparsely setose. Merus finely granulate, with few slender spines, longest distoventrally. Carpus granulate and with long, slender spines. Propodus palm surfaces with long, slender spines, longest along dorsal and ventral margins, extending onto pollex. Dactylus longer than dorsal palm length; proximal three-fourths spinose; outer surface with faint longitudinal carina, occlusal surfaces of dactylus and pollex crenulate, without gape when fingers closed.

Pereopods 2 and 3, sparsely setose, flexor and extensor margins spinose, other surfaces granulate, minutely spinose; longest spines on extensor margins of propodus and carpus; merus extensor and flexor margins with short spines dactylus broadly curved, sparsely and minutely spinose proximally, otherwise smooth, without distinct longitudinal rib. Pereopod 3 longest, merus 0.97 pcl (female); dactylus slightly shorter than combined length of propodus and carpus.

Pereopods 4 and 5 finely granulate, minutely 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; propodus setose. Pereopod 5 merus, when folded against carapace, reaching anterior 1/4 of carapace.

Thoracic sternite 3 pentagonal, width twice length; lateral margins 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 without trace of demarcation between somite 6 and telson; rounded, sparsely granulate or minutely spinose; margins straight to slightly convex; apex rounded; width 2.0 × length (female).

Etymology. Named brevis, Latin adjective for short, alluding to the single instead of bifid or trifid epistomial spine mesial to the base of the antenna and reduced carapace granulation relative to its morphologically and geographically nearest relative, C. bathamae .

Remarks. Cymonomus brevis sp. nov., a member of the C. bathamae group, is most closely related to C. bathamae . The new species differs from C. bathamae in having more sparsely distributed carapace granules ( Fig. 8A ), a single instead of bifid or trifid epistomial spine mesial to the base of the antenna ( Fig. 8C ), a more slender rostrum ( Fig. 8D ) (length exceeding, versus distinctly less than, twice basal width), proportionally longer pereopod 3 ( Fig. 8A ) (as long as pcl versus 0.87–0.93 pcl) and a proportionally broader telson ( Fig. 8B ). Cymonomus brevis sp. nov. might also mature at a smaller size than C. bathamae . The holotype of C. brevis sp. nov. has an abdomen of fully mature form and appears to be “spent”, whereas the smallest female C. bathamae (pcl 3.3 mm), despite being larger than the holotype of C. brevis (pcl 2.8 mm), has a proportionally narrower, “pre-spawning” abdomen (also cf Dell, 1971: fig. 4). The smallest known ovigerous female of C. bathamae measures 3.7 mm pcl (NIWA 68021).

Distribution. Known only from the Bay of Plenty, New Zealand ( Fig. 9 ); 151 m.

Figures

Figure 8. Cymonomus brevis sp.nov., female holotype, cl 3.9 mm, pcl 2.8 mm, cw 3.3 mm, Bay of Plenty, New Zealand, NIWA 76191. (A) dorsal habitus; (B) posterior abdomen; (C) right epistomial spine mesial to base of antenna; (D) fronto-orbital region; (E) right maxilliped 3; (F) thoracic sternite 3. Scale: A–B = 1.0 mm; C = 0.25 mm; C–F = 0.5 mm.

Figure 9. Cymonomus brevis sp. nov., distribution.