Orthotheres turboe Sakai 1969

Orthotheres turboe Sakai, 1969

(Figs. 1–3)

Orthotheres turboe Sakai, 1969: 275, pl. 2 figs. 1, 2; text fig. 19a; Sakai, 1976: 574, text figs. 314a–c; Miyake, 1983: 242 (list); Miyake, 1998: 242 (list); Ng et al., 2008: 250 (list).

Material examined. Holotype: ovigerous female (12.7 × 9.1mm) (USNM 125889), in stomach of Turbo argyrotomus Linnaeus, 1758 (Turbinidae), Yoron Island, Amami Islands, Ryukyu Islands, Japan, coll. K. Sakai & H. Yamada, late 1960s. Paratype: 1 male (4.8 × 4.5 mm) (USNM 126231), same data as holotype.

Diagnosis. Female: Carapace transversely ovate, wider than long, width to length ratio 1.39; dorsal surface smooth, glabrous, distinctly convex; front projecting slightly anteriorly beyond orbits, entire, margin distinctly sinuous with prominent median concavity (Figs. 1B; 2A). Eyes small, just visible in dorsal view; mobile, completely filling orbit (Fig. 2A). MXP3 outer surface with scattered short setae; dactylus elongate, inserted distinctly before base of propodus; propodus about 2 times length of dactylus, cylindrical, as long as subovate carpus; carpus inserted on inner surface of ischiomerus, just below distal margin; ischiomerus long, articles completely fused, anteromesial angle of merus angular to weakly angularfrom lateral view; exopod relatively stout, ca. 1/2 length of ischiomerus, flagellum 2–segmented (Fig. 2B, C). Anterior thoracic sternum wide sternites 1, 2 completely fused (Fig. 2E). Chela long; mesioventral margin distinctly setose; outer surfaces of palm, fingers (except for distal and marginal parts) almost smooth; ventral parts of inner surface with numerous setae which do not obscure surface; fingers ca. half length of palm; dactylus occlusal margin with large subproximal tooth, with 3 or 4 denticles behind it; pollex occlusal margin with 1 subproximal tooth, with 2 or 3 denticles behind it (Fig. 3C). Ambulatory legs short, left and right sides symmetrical; P2–P4 merus relatively long; P5 propodus elongate; no natatory setae present; relative lengths of meri P2<P3=P4>P5; dactylus short with prominently hooked tip, ventral margin lined with short setae; P3 and P4 dactylus relatively shorter, broader, dorsal margin carinate, ventral surface forming gently but prominently concave surface (Fig. 3A, B, D–H). Abdomen wide, extending to buccal region, covering bases of ambulatory legs; telson deeply recessed into distal margin of somite 6 with gently sinuous distal margin (Fig. 2D).

Male: Carapace circular, slightly wider than long, width to length ratio 1.07; dorsal surface smooth, gently convex; front distinctly projecting anteriorly, margin prominently sinuous (Figs. 1A, 2F). Eyes distinctly visible in dorsal view (Figs. 1A; 2F). MXP3 as in female (Fig. 2G). Anterior thoracic sternum relatively wide sternites 1, 2 fused, with shallow concave suture (towards buccal cavity) separating from sternite 3; sternites 3, 4 fused, with very shallow groove separating them; sternoabdominal cavity reaching to just before suture between sternites 3/4. Chela relatively stout, shorter than in female; occlusal margin of fingers with distinct subproximal tooth and 3 or 4 denticles behind it (Fig. 2I). Ambulatory legs short, left and right sides symmetrical; P5 propodus short; no natatory setae present; relative lengths of meri P2=P3=P4>P5; dactylus short with prominently hooked tip, ventral margin lined with short setae; P3 and P4 dactylus with ventral surface gently concave (Fig. 3 J–M). Abdomen relatively wider; telson semicircular (Fig. 2H). G1 relatively stout, distal third gently curved outwards, tip with distinct dorsal opening (Fig. 2 I–K). G2 short, with subspatuliform tip; exopod stout, almost as long as endopod (Fig. 2L).

Remarks. Sakai (1969: 277) stated that a female (presumably the holotype) was 13.0 by 8.5 mm while a male specimen was 5.1 by 5.0 mm. The present holotype female measures 12.7 × 9.1 mm and the paratype male is 4.8 × 4.5 mm. The holotype female and paratype specimens examined agree with those he figured (Sakai, 1969: pl. 2 figs. 1, 2). The MXP3 of the species, as figured by Sakai (1969) is misleading. It was clearly drawn in situ from the inner surface, with the structure still attached to the specimen and probably also at an angle, making it appear longer; and the propodus and dactylus very short (Sakai, 1969: fig. 19a). The MXP3 is actually less elongate, and the propodus and dactylus much longer (Fig. 2B).

For comparisons with O. haliotidis and O. baoyu n. sp., see remarks for the latter species.