Orbicantha sacrebleu, Ng & Forges & Lee, 2023

Ng, Peter K. L., Forges, Bertrand Richer De & Lee, Bee Yan, 2023, New and rare deep-sea majoid crabs (Crustacea: Brachyura) from Papua New Guinea, Zootaxa 5318 (1), pp. 1-44 : 25-30

publication ID	https://doi.org/ 10.11646/zootaxa.5318.1.1
publication LSID	lsid:zoobank.org:pub:DB9D6B30-5A8C-486A-BF67-0965E4C026DA
DOI	https://doi.org/10.5281/zenodo.8158149
persistent identifier	https://treatment.plazi.org/id/9B094F56-FA50-FFE7-FF20-C25BFEF6FA94
treatment provided by	Plazi
scientific name	Orbicantha sacrebleu
status	n. gen., n. sp.

Treatment

Orbicantha sacrebleu View in CoL n. gen., n. sp.

( Figs. 1G, H View FIGURE 1 , 19–22 View FIGURE 19 View FIGURE 20 View FIGURE 21 View FIGURE 22 )

Type material. Holotype: female (cl 8.0 mm, pcl 7.2 mm, cw 7.9 mm, pcw 7.1 mm) (MNHN-IU-2014-8158), stn CP 4489, New Ireland, Papua New Guinea, 02°24’S 149°59’E, 175 m, coll. N.O. Alis, BIOPAPUA cruise, S. Samadi & L. Corbari, 6 September 2014 GoogleMaps . Other material examined. 2 females (cl 6.8 mm, pcl 6.2 mm, cw 7.2 mm, pcw 6.4 mm; cl 7.1 mm, pcl 6.7 mm, cw 7.5 mm, pcw 6.4 mm) ( ZRC 2022.0083 View Materials ), station AT17, west Malo Island , Vanuatu, 15°39.9'S 167°0.20'E, 267–270 m, coll. N.O. Alis, SANTO 2006 expedition, 21 September 2006 GoogleMaps .

Diagnosis. As for genus.

Description. Small species, pcl less than 8 mm; carapace semicircular, slightly wider than long; gastrohepatic and frontal regions not elongated, lateral constriction with branchial regions weak ( Figs. 19A, B View FIGURE 19 , 22A, B View FIGURE 22 ). Dorsal surface not swollen, gently convex with regions clearly visible, gastro-cardiac-branchial grooves deep; mesogastric region with 1 median spine with rounded tip; protogastric region with 2 small spines arranged obliquely; metagastric region with 1 median spine with rounded tip cardiac region with 2 short spines positioned side by side; intestinal region with 1 large median tubercle and 1 short spine lateral to it on each side; hepatic region gently convex, not prominently swollen with 2 or 3 spines with round tips; branchial region with oblique median row of 3 spines (some round-tipped); lateral branchial margin with 6–8 large and many small spines (larger ones round-tipped); posterior carapace margin with 2 slightly large spines compared to rest of spines; rest of dorsal carapace surface with numerous distinct rounded granules and scattered setae; H-shaped gastro-cardiac groove visible ( Figs. 19A–E View FIGURE 19 , 22A–C View FIGURE 22 ). Pterygostomial region protruding anteriorly, forming angular shelf-like structure in lateral view, upper margin lined with prominent granules, appears finely crenulated, pressing into narrow suborbital region ( Fig. 19D, E View FIGURE 19 ); sub-branchial and subhepatic regions granulated. Pseudorostrum short, as long as supraorbital eave, base wide with 2 distal spines, outer one shorter, longer inner spine with rounded tip; interantennular spine distinct, tip bifurcated, clearly visible in dorsal view; postorbital spine gently curved with rounded tip, slightly larger than intercalated spine with rounded tip; antorbital spine ca. half length of intercalated spine, margin of supraorbital eave with 4 short spines, no obvious preorbital spine ( Figs. 19B, C, F View FIGURE 19 , 20B View FIGURE 20 , 22B View FIGURE 22 ). Basal antennal article elongate, outer margin lined with short spines, median part with longitudinal row of sharp granules, with 2 distal spines on ventral edge, 1 dorsal spine on dorsal edge; third article short, subquadrate, ca. one-third length of basal article ( Fig. 19F View FIGURE 19 ). Eyes with short, stout peduncle; cornea prominent with 3 or 4 tubercles on dorsal surface, those adjacent to peduncle stronger ( Fig. 19C, F View FIGURE 19 ). Epistome is distinctly quadrate, posterior margin with median part triangular, lateral part prominently concave ( Fig. 19F View FIGURE 19 ); buccal cavity wide ( Fig. 20B View FIGURE 20 ).

Outer surface of third maxilliped covered with sharp and rounded granules, those on inner margins sharper, larger; internal border of basis-ischium denticulate, with 1 large outwardly directed sharp tubercle; ischium subrectangular, shallow median suboblique sulcus just visible; outer margin denticulate, lined with dense stiff setae; merus subtriangular, proximal margin lined with strong sharp tubercles, anteroexternal angle expanded, auriculiform, margin with spines; exopod slender, tip reaching beyond distal edge of merus, with median row of tubercles, with long flagellum ( Fig. 20A View FIGURE 20 ).

Chelipeds slender, relatively short; symmetrical ( Fig. 19A View FIGURE 19 , 22A View FIGURE 22 ). Coxa quadrate, with strong curved short spine on ventral distal corner. Basis-ischium short, covered with sharp granules, with 2 larger sharp tubercles on dorsal margin; merus lined with sharp tubercles and granules on outer and ventral margins, inner margins with lower, blunter tubercles; carpus subcylindrical, covered with low sharp tubercles and granules ( Figs. 20D View FIGURE 20 , 21A View FIGURE 21 ). Chelae slender, not inflated; outer surface of palm with numerous granules and low tubercles, margins with 3–6 long gently curved spines; fingers longer than palm, almost straight, cutting margins with low teeth ( Fig. 20C, D View FIGURE 20 ).

Ambulatory legs relatively long, slender; P2 longest ( Figs. 19A View FIGURE 19 , 22A View FIGURE 22 ). P2 and P3 merus lined with prominent long and short spines with scattered long setae, those on ventral margin longer; carpus with short spines on margin, those on ventral margin longer; propodus and dactylus with short spines and stiff setae on dorsal margins, ventral margin with long stiff setae that resemble spines and setae, appearing comb-like; outer surfaces of merus, carpus and propodus with small round granules ( Figs. 19A View FIGURE 19 , 20E, F View FIGURE 20 , 22A View FIGURE 22 ). P4 and P5 prominently reduced in size, more slender compared to P2 and P3; merus with low spines and setae on ventral margin, dorsal margin with scattered setae but unarmed; P4 carpus with sharp granules on ventral margin, dorsal margin unarmed; P5 carpus unarmed; margins of propodus and dactylus without long spines or long stiff setae; ventral margin of propodus with sharp granules and denser soft setae; dactylus with denser soft setae on dorsal margin; outer surfaces of merus with scattered low granules, carpus and propodus smooth ( Figs. 19A View FIGURE 19 , 20G, H View FIGURE 20 , 22A View FIGURE 22 ).

Thoracic sternum wide; sternites 1 and 2 fused to form triangular plate with convex lateral margins; sternites 2 and 3 separated by clear suture; sternites 3 and 4 completely fused medially with only lateral constriction demarcating sternites; sternite 4 with prominent broad V-shaped ridge medially that demarcates sternopleonal cavity, proximal half with prominent sharp granules on median part, lateral parts smooth; sternites 4/5, 5/6, 6/7 and 7/8 medially interrupted; vulvae on anterior part of sternite 6, subovate, with narrow rim ( Fig. 21A, B View FIGURE 21 ).

Pleon subcircular in shape, domed; covering most of thoracic sternum; somites 1–5 free but barely mobile; somite 6 and telson functionally fused but suture visible on outer surface, not visible on inside surface; surface of pleon covered in small sharp granules; somite 1 broad, rectangular, posterior margin with several larger spines; somite 2 subtrapezoidal, median part and lateral angles with longer spines; somites 3–5 trapezoidal; somite 6 as long as semicircular telson ( Fig. 21A, C, D View FIGURE 21 ).

Colour. The carapace, chelipeds and P2 and P3 are reddish-orange to orange with the spines white, with the P4 and P5 being white to dirty grey ( Fig. 1G, H View FIGURE 1 ).

Etymology. “Sacrebleu” is an ancient French exclamation of surprise and is used here to reflect our very unexpected discovery of the present new genus. The name is used as a Latin noun in apposition.

Remarks. Little is known about the ecology of Orbicantha sacrebleu n. sp. except that it was collected from relatively shallow water (175 m) for a pleistacanthine. The holotype is clearly an adult female, with the female pleon fully ovate and the pleopods setose, and the vulvae well developed. The unusual features of the type species are therefore adult characters. We have examined numerous juvenile specimens of Pleistacantha and Pleisticanthoides , and while they tend to be less elongate and somewhat less pyriform, they invariably have relatively large eyes and their pleon, gonopods and/or pleopods are absent or poorly developed. None possess the characters that define the present new genus.