Orthotheres baoyu Ng & Ho 2016, n. sp.
Creators: name: Ng, Peter K. L.
name: Ho, Ping-Ho
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Pinnotheridae
Orthotheres
Orthotheres baoyu

description: Orthotheres baoyu n. sp.
(Figs. 7–9)
Material examined. Holotype: ovigerous female (12.7 × 9.4 mm) (NTOU CP 20020627a), from 8.5 cm long abalone (Haliotis asinina Linnaeus, 1758; Haliotidae), Tungsha islands, Taiwan, coll. M.-H. Chen, 27 June 2002. Paratype: 1 poorly preserved female (8.6 × 7.1 mm) (NTOUCP 20020627b), same data as holotype.
Diagnosis. Female: Carapace transversely ovate, wider than long, width to length ratio 1.35; dorsal surface smooth, glabrous, gently convex; front projecting slightly anteriorly beyond orbits, entire, margin gently sinuous with shallow median concavity (Figs. 7A, B; 8A). Eyes small, just visible in dorsal view; mobile, completely filling orbit (Figs. 7B; 8A). MXP3 outer surface with numerous short plumose 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, below distal margin; ischiomerus very long, articles completely fused, anteromesial angle of merus rounded from lateral view, subangular from submesial view; exopod relatively stout, ca. 1/2 length of ischiomerus, flagellum 2–segmented (Fig. 8 D–F). Anterior thoracic sternum wide sternites 1, 2 completely fused. Chela relatively 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 no denticles behind it; pollex occlusal margin with 1 subproximal tooth, with no denticles behind it (Fig. 8C). 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. 9). Abdomen wide, extending to buccal region, covering bases of ambulatory legs; telson deeply recessed into distal margin of somite 6 with distinctly sinuous distal margin (Fig. 8B). Male: not known.
Etymology. The species name is derived from the Chinese name for abalone, “bao-yu”. The name is used as a noun in apposition.
Remarks. The three species differ in various characters. For well-preserved female specimens, the dorsal carapace surface of O. haliotidis (Fig. 4C) and O. turboe (Fig. 1C) is distinctly more convex compared to that of O. baoyu n. sp. (Fig. 7B). Although the carapace width to length ratios do not reflect it, the carapace of O. turboe appears to be the widest because posterolateral parts are more prominently expanded laterally (Figs. 1B; 2A); in O. haliotidis and O. baoyu, the posterolateral areas are only gently convex (Figs. 4B; 5A; 7A; 8A). The frontal margin of O. turboe is diagnostic in that it is distinctly sinuous, with the median part prominently concave (Figs. 1B; 2A). In O. haliotidis and O. baoyu, the frontal margin is only slightly sinuous with the median part gently concave (Figs. 4B; 5A; 8A). The MXP3 are distinct for O. baoyu; it has the most prominently elongated ischiomerus, with the anteromesial part rounded when it is lying flat (Fig. 8D). In O. turboe and O. haliotidis, the ischiomerus is relatively shorter (Figs. 2D, G; 5B, D) with the anteromesial part somewhat weakly angular to angular in O. turboe (Fig. 2D, G) and distinctly angular in O. haliotidis (Fig. 5B, D; Geiger & Martin, 1999: figs. 3A, 4). In O. baoyu, only when the ischiomerus is tilted at a 30° angle does the anterointernal part appear angular (Fig. 8E), but is distinctly rounded when it is observed flat down (Fig. 8D). The female chela of O. baoyu is distinct in that it is proportionately the longest, and the occlusal margin behind the large subproximal tooth on each finger is entire (Fig. 8C). In O. turboe and O. haliotidis, the female chelae are distinctly shorter and the occlusal margin behind the large subproximal tooth on each finger is lined with several denticles (Figs. 3C; 6M). The proportions of the ambulatory legs differ. In O. turboe and O. baoyu, the merus of P2–P4 is proportionately longer (Figs. 3A, D, F; 9 A–G) than in O. haliotidis (Fig. 6F, G, I). For the P5, the propodus of O. turboe and O. baoyu (Figs. 3B, H; 9H, I) is distinctly longer than that of O. haliotidis (Fig. 6H, K). The female abdomen is relatively widest in O. turboe (Fig. 2B) compared to those of O. haliotidis (Fig. 5G, H) and O. baoyu (Figs. 8C; 9B). In males, the carapaces do not differ substantially. However, the frontal margin of the male O. turboe (Figs. 1A; 2F) is like that of the female, being distinctly more sinuous than that of O. haliotidis (Fig. 4A). There are no major differences in the structure of the MXP3 between the sexes of the two species (O. turboe and O. haliotidis) in which males and females are known (e.g., Fig. 2B, G). The male chelae of O. turboe and O. haliotidis are also very similar in shape and proportions (Figs. 3I; 6L). For the ambulatory legs, the P5 propodus of O. turboe (Fig. 3M) is proportionately shorter than that of O. haliotidis (Fig. 6D). The male abdomens of the two species also differ, with that of O. turboe (Fig. 2H) being transversely broader than that of O. haliotidis (Fig. 5F). The G1s of O. turboe and O. haliotidis are very similar, but the distal third of O. turboe (Fig. 2I, J) is more gently curved than that of O. haliotidis, which is more distinctly bent (Fig. 5I, K).
In any case, their hosts are different: O. turboe has been found only with the top shell Turbo (cf. Sakai, 1969: 277) while O. baoyu and O. haliotidis are from the same species of abalone.
description: Published as part of Ng, Peter K. L. & Ho, Ping-Ho, 2016, Orthotheres baoyu, a new species of pea crab (Crustacea: Brachyura: Pinnotheridae) associated with abalones from Tungsha Island, Taiwan; with notes on the genus, pp. 229-241 in Raffles Bulletin of Zoology 64 on pages 236-240, DOI: 10.5281/zenodo.4502042