Pedroplax megalops Takeda 1989, new combination
Creators: name: Ng, Peter K. L.
name: Komai, Tomoyuki
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Goneplacidae
Pedroplax
Pedroplax megalops

description: Pedroplax megalops (Takeda, 1989) new combination
(Figs. 1–3)
Psopheticus megalops Takeda, 1989: 172, figs. 16, 17; Castro 2007: 738, 739. Psopheticus megalops —Ng et al. 2008: 80.
Material examined. Holotype: male (5.6× 4.8 mm) (NSMT-Cr 9754), Oshima Passage, 25–40 m depth, coll. Kagoshima University, 29 June 1970. Paratype: female (5.1× 4.4 mm) (NSMT-Cr 5297), east of Tanegashima, ca. 59 m depth, coll. M. Takeda & M. Imajima, 18 June 1975. Others: 1 male (5.2× 4.4 mm) (CBM-ZC5936), south of Amuro Island, Kerama Group, Ryukyu Islands, 2610.00’N, 12718.90’E, 52 m, dredge, station 7, coll. T. Komai, TRV Toyoshio-maru, 1998-4 cruise, 19 May 1998; 2 ovigerous females (4.2× 3.7 mm, 4.4×4.0 mm) (CBM-ZC 7623), north of Yakabi Island, Kerama Group, Ryukyu Islands, 55–101 m, 2615.34’N, 12715.98’E, dredge, station E-6, coll. T. Komai, RV Tansei-maru, KT02-3 cruise, 19 April 2002; 1 ovigerous female (3.9× 3.5 mm) (ZRC 2011.0203), off Nagannu Island, Okinawa Islands, 2614.64’N, 12731.01’E, 51 m, dredge, coll. TRV Toyoshiomaru, 2005 cruise, 22 May 2005.
Description of male. Carapace quadrate, longer than broad, 1.1–1.2 times broader than long (Figs. 1, 3 A). Dorsal surface glabrous, almost smooth but with numerous minute low granules; granules relatively more prominent along frontal, anterolateral margins; H-shaped gastro-cardiac groove deep (Figs. 1, 3 A). Front entire, median part gently concave, short sulcus separating it from low lateral lobe (Figs. 1, 2 A, 3A). Orbit short, ovate; eyes relatively large, mobile, cornea large, protruding beyond outer margin of orbit, ocular peduncle very short, distal part with numerous small granules (Figs. 1, 2 A, 3A). Supraorbital margin entire, no trace of external orbital angle or tooth (Figs. 1, 2 A, 3A). Suborbital margin sinuous, entire, resembling rim around eye, with low inner sublobiform tooth (Fig. 2 A, C). Anterolateral margin very short, gently concave, lateral tooth prominent but not sharp, sublobiform, gently curving obliquely anteriorly, upwards (Figs. 1, 2 A, 3A). Posterolateral margins gently converging towards posterior carapace margin; region just behind anterior part of posterolateral margin gently swollen, with low rounded crest posteriorly (Figs. 1, 2 B, 3A). Posterior carapace margin gently concave (Figs. 1, 2 B, 3A). Hepatic, ptergostomial, subhepatic regions appear smooth but covered with numerous minute low granules (Fig. 2 A). Antennule relatively large, fossa asymmetrical with outer margin longer than inner, distal segments folding transversely (Fig. 2 A). Basal antennal segment mobile, rectangular; flagellum relatively short, as long as width of orbit, lodged inside orbit (Fig. 2 A). Epistome relatively broad, anterior part triangular; posterior margin sinuous with 3 low median lobes, separated from lateral parts by deep concavity (Fig. 2 A). Endostomial ridges well developed. Third maxillipeds subquadrate, forming small basal gape medially when closed, gets wider anteriorly; merus about as long as wide, anterolateral angle rounded, not auriculiform; ischium subrectangular, very shallow, barely discernible sulcus. Exopod slender, reaching anterior margin of merus, with prominent tooth on inner subdistal margin; flagellum long (Figs. 2 C, 3B).
Chelipeds homochelous, asymmetrical; surfaces almost glabrous, smooth (Fig. 1, 3 C, D). Merus short, with low rounded tooth on subproximal dorsal margin, margins gently granular (Figs. 1, 3 C). Carpus with large, obtuse lobiform tooth on inner angle (Figs. 1, 3 C, D). Chela stout, fingers laterally flattened, longer than palm, cutting edges with uneven cutting teeth (Fig. 3 D).
Ambulatory legs slender, articles smooth, with scattered plumose, simple setae; second leg longest (Fig. 1). Meri slender, dorsal margins gently serrated, without trace of distal or subdistal angle (Figs. 1 B, C, 3E). Propodi laterally flattened with median sulcus, that of fourth leg ovate, subfoliaceous (Figs. 1 B, C, 3E). Dactyli slender, covered with very short setae but not obscuring surface, gradually tapering to distal part, gently curved distally; that of fourth leg laterally flattened, subspatuliform, broadest medially (Fig. 1 B, C).
Surface of thoracic sternites covered with low, small granules, appearing almost smooth. Sternites 1, 2 completely fused, forming prominent triangular plate, separated from sternite 3 by shallow but distinct suture (Figs. 2 C, D). Sternites 3, 4 completely fused except for lateral sutures; sutures between sternites 4–8 medially interrupted; longitudinal groove present between sternites 6–8. Press button of abdominal locking mechanism present as prominent, rounded tubercle on anterior half of sternite 5 (Figs. 2 D). Penis coxal, opening to base of G1 through narrow channel formed by episternite 7, sternite 8 (Fig. 2 E).
Sterno-abdominal cavity relatively broad; male abdomen reaching to level between posterior edges of coxae of chelipeds (Fig. 2 C, D). Abdomen relatively broad, broadly T-shaped, all somites, telson free. Somite 1 longitudinally narrow, reaching to bases of coxae of last ambulatory legs; somite 2 almost twice height of somite 1, not reaching base of legs, large part of sternite 8 exposed; somite 3 transversely trapezoidal, almost reaching coxae of last ambulatory legs except for narrow part of sternite 8 (Figs. 2 B, 3G); somites 4, 5 trapezoidal; somite 6 rectangular, lateral margins almost parallel (Fig. 2 C, 3F); telson triangular with strongly convex lateral margins, rounded tip (Figs. 2 C, 3F).
G1 relatively stout, gently curved outwards, distal quarter tapering to sharp tip, with 2 stout subdistal spines on outer margin (Fig. 3 H, I). G2 slender about 1.3 times length of G1, median part dilated with numerous short spines on outer margin, distal part elongated, tip bifurcated with 4 or 5 subdistal spines (Fig. 3 J, K).
Female characters. The female chelae are similar to that of the males in form but weaker and relatively more slender. The abdomen is rounded, covering the entire thoracic sternum with all the somites free. The telson is broadly triangular with lateral margins gently sinuous but not contiguous with the margins of somite 6. There is no visible abdominal locking press-button structure. The vulvae are prominent, occupying most of anterior half of sternite 6, without visible sternal vulvar cover (Fig. 2 F).
Remarks. There are a surprisingly small number of eggs for the three ovigerous females examined. The two larger females (4.2× 3.7 mm and 4.4×4.0 mm, CBM-ZC7623) had 15 and 24 eggs respectively, while the smaller female (3.9× 3.5 mm, ZRC 2011.0203) had 25 eggs. The relatively large size (ca. 0.5–0.6 mm in diameter), especially in relation to the small size of the female, and small number of eggs suggest the larvae may be partially or perhaps even fully abbreviated (e.g., see Tan et al. 1986).
Pedroplax megalops is so far known only from southern Japan. It has been dredged from depths of 25 to 101 m.
description: Published as part of Ng, Peter K. L. & Komai, Tomoyuki, 2011, A new genus for Psopheticus megalops Takeda, 1989 (Crustacea: Brachyura: Goneplacidae), pp. 61-67 in Zootaxa 2934 on pages 62-63, DOI: 10.5281/zenodo.203270