Pronotonyx laevis ( Miers, 1884 )

Ahyong, Shane T. & Ng, Peter K. L., 2023, On the identity of Pronotonyx laevis (Miers, 1884) (Crustacea: Brachyura: Pilumnidae), Zootaxa 5293 (2), pp. 392-400 : 394-398

publication ID	https://doi.org/ 10.11646/zootaxa.5293.2.12
publication LSID	lsid:zoobank.org:pub:C42E6A04-811B-4E8C-98CE-0E131FDEF330
DOI	https://doi.org/10.5281/zenodo.7959933
persistent identifier	https://treatment.plazi.org/id/03A2995B-FFDC-FFF1-24F7-FC14FE3C1301
treatment provided by	Plazi
scientific name	Pronotonyx laevis ( Miers, 1884 )
status

Treatment

Pronotonyx laevis ( Miers, 1884) View in CoL

( Figs. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Ceratoplax View in CoL ? laevis Miers, 1884: 244 View in CoL , pl. 25 fig. C.— Tesch 1918: 203.

Pronotonyx laevis View in CoL .— Ward 1936: 2, pl. 1 figs. 4–6.— Ng 1987: 79, 98.— Davie 2002: 426 (list).—Ng et al. 2008: 144 (list).

Type material. HOLOTYPE: NHM 1882.7, female (cl 5.0 mm, cw 6.5 mm), Arafura Sea, 32–36 fathoms, dredged, HMS Alert.

Other material examined. AM P93048 , 3 males (cl 9.8 mm, cw 13.1 mm to cl 10.3 mm, cw 13.5 mm), 3 females (cl 8.1 mm, cw 11.3 mm to cl 9.5 mm, cw 13.2 mm), Lindeman Island , Queensland, Australia, coll. M. Ward , 1933; ZRC 2023.0030 View Materials , 1 male (cl 9.8 mm, cw 13.1 mm), 1 female (cl 8.1 mm, cw 11.3 mm), Lindeman Island , Queensland, Australia, coll. M. Ward , 1933; NHM 1937.7.15.18–19, 2 females (cl 5.5 mm, cw 7.3 mm; cl 3.8 mm, cw 5.0 mm), Lindeman Island , Queensland, Australia, coll. M. Ward , 1933.

Diagnosis. As for genus.

Description. Males. Carapace subquadrate, 1.32–1.39 × wider than long; dorsal surface gently convex in anterior half, regions not defined, surface very smooth, polished, without granules or rugosities, frontal and anterolateral margins almost glabrous, with scattered. coarse setae, never fully obscuring margins or surface ( Fig. 2A, B View FIGURE 2 ). Frontal margin slightly produced, deflexed downwards, with 2 very low lobes, barely separated by very shallow concavity; lateral lobe not visible; with scattered coarse setae just posterior to margin ( Fig. 2A, B View FIGURE 2 ). Anterolateral margin gently convex; external orbital tooth very low, almost undiscernible, not demarcated from remainder of smooth to weakly granulated margin, entire or at most with 3 very low barely discernible lobes ( Fig. 2A, B View FIGURE 2 ). Posterolateral margin almost straight or slightly concave, distinctly converging to almost straight posterior carapace margin ( Fig. 2A, B View FIGURE 2 ). Suborbital, subhepatic, pterygostomial and sub-branchial regions smooth ( Fig. 2D, E View FIGURE 2 ). Orbit transverse, large; supraorbital margin almost straight, entire; suborbital margin gently sinuous, entire, without tooth on inner angle; eyes large with short peduncle and large cornea ( Fig. 2B, D, E View FIGURE 2 ).

Antennular fossa rectangular, antennule folding transversely ( Fig. 2D, E View FIGURE 2 ).Antenna with basal article subquadrate, immobile with epistome but sutures visible, articles 3 and 4 distinctly shorter than basal article, flagellum short, just entering orbit ( Fig. 2D, E View FIGURE 2 ). Epistome longitudinally wide; buccal margin wide, sinuous medially obtuse with median fissure, separated from convex lateral lobes by short fissure ( Fig. 2D, E View FIGURE 2 , 4F View FIGURE 4 ). Endostome with low oblique ridge on each half.

Maxilliped 3 relatively short; merus quadrate, anteroexternal angle auriculiform; ischium subrectangular with shallow oblique median sulcus; exopod relatively broad, tip almost reaching distal edge of merus, with long flagellum ( Fig. 2C View FIGURE 2 ).

Chelipeds stout, size asymmetrical, similar in structure Basis-ischium almost smooth on ventral margin; merus short, with blunt dorsal tooth in adults. Carpus dorsal surface smooth; inner distal margin with low, acute, tooth; distal margins with fringe of short and long setae ( Fig. 2A, F View FIGURE 2 ). Chela outer surface smooth, glabrous, dorsal margins distinctly setose; palm high; pollex almost as long as or subequal to palm, with distinct keel on ventral margin of palm; dactylus oriented obliquely, when flexed, inclined at angle not exceeding 45° to the vertical; occlusal margins of fingers with low, wide teeth, gape absent to slight ( Fig. 2F View FIGURE 2 ).

Ambulatory legs (P2–5) relatively long, slender, smooth; margins covered with short pubescence; P3 longest (merus 0.71–0.74 × cl), P5 shortest. Merus without cristae on dorsal margin, entire. Carpus and propodus smooth. P2–P4 dactylus falciform, gently curved along most of length, tip hooked, almost glabrous. P5 dactylus shorter, slightly upcurved ( Fig. 2A View FIGURE 2 ).

Thoracic sternum relatively wide, smooth. Sternites 1 and 2 completely fused to form triangular structure with weakly concave lateral margins. Sternites 2 and 3 separated by distinct suture. Sternites 3 and 4 fused but oblique lateral depression demarcating sternites visible. Sternites 1–4 width 1.7 × length in males ( Fig. 4G View FIGURE 4 ). Sternopleonal cavity reaching level of midlength of cheliped coxae ( Fig. 2H, G View FIGURE 2 ). Sternite 8 exposed when pleon closed, visible as subtriangular plate ( Fig. 2I View FIGURE 2 ). Penis long, at condyle of P5 coxa, positioned in short, partially exposed coxosternal groove.

Male pleon triangular, T-shaped, all somites and telson free ( Figs. 2G–I View FIGURE 2 , 4H View FIGURE 4 ). Somite 1 widest, reaching to P5 coxae. Somite 2 much narrower than somites 1 and 3. Somite 3 wide, almost reaching condyles of P5 coxae. Somites 4–6 transversely narrow; somites 4 and 5 trapezoidal with gently concave margins; somite 6 rectangular. Telson linguiform, longer than wide ( Figs. 2G, H View FIGURE 2 , 4H View FIGURE 4 ).

G1 strongly sinuous, distal part strongly curved, hooked, elongate ( Fig. 4I View FIGURE 4 ). G2 short, sigmoid, tip spatuliform ( Fig. 4J View FIGURE 4 ).

Females. Chelipeds symmetrical, proportionally smaller ( Figs. 1A, B View FIGURE 1 , 3A–C, E View FIGURE 3 ) and ambulatory legs slightly shorter (P3 merus 0.67–0.70 × cl) than in males, otherwise similar to males in all non-sexual characters. Female pleon longitudinally subovate, not covering entirety of thoracic sternum; telson broadly linguiform, as long as wide; somite 1 narrow, very wide, reaching to P5 coxae ( Fig. 3G View FIGURE 3 ). Vulvae on anterior half of sternite 6, obliquely positioned, subovate, without operculum ( Fig. 3H View FIGURE 3 ).

Remarks. The series of Pronotonyx laevis examined has permitted documentation of adults of both sexes. We note two misinterpretations in previous accounts (Miers 1886; Ward 1936) in that a blunt dorsal tooth is present on the dorsal margin of the cheliped merus in adults (weakly developed in the juvenile female holotype), and the male pleonal somite 1 reaches (rather than almost reaches) the P5 coxae. Ward (1936: 4) listed two males and three females from Lindeman Island in his study. There are altogether 10 specimens (AM P93048, ZRC 2023.0030, NHM 1937.7.15.18–19) all from the same locality, collected by Ward; it is unclear which of these specimens were those Ward recorded in his 1936 paper.

The holotype female was dredged from depths of 58.5–65.8 m in the Arafura Sea. Ward (1936: 3) stated that the “species occurs in deep water in the vicinity of Lindeman Island where I have dredged it on mud”; nothing else is known about its ecology.