Orientotlos iishibai Sakai, 1980

Ng, Peter K. L. & Chan, Tin-Yam, 2021, Rediscovery of Orientotlos iishibai Sakai, 1980 (Crustacea, Decapoda, Brachyura, Leucosiidae) in Taiwan, ZooKeys 1053, pp. 185-195 : 185

publication ID	https://dx.doi.org/10.3897/zookeys.1053.67326
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scientific name	Orientotlos iishibai Sakai, 1980
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Orientotlos iishibai Sakai, 1980 View in CoL

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4

Orientotlos iishibai Sakai, 1980: 74, text-fig. 1. - Ng et al. 2008: 92 (list).

Material examined.

Taiwan • 1 ♀ ovigerous (7.8 × 6.5 mm); station CP4210, off southwestern Taiwan coast; 22°18.94'N, 120°20.57'E; depth 116-159 m; 14 Nov. 2020; T.-Y. Chan leg.; hard bottom substrate; NTOU B00125 View Materials GoogleMaps .

Diagnosis.

As for genus.

Description.

Female. Carapace subhexagonal in outline, 1.2 × as wide as long; upper surface (between plates and bosses) paved with numerous, well-spaced boletiform and rounded tubercles of varying sizes (Figs 1 View Figure 1 , 2A-D View Figure 2 ). Front produced, upturned, margin weakly bilobed with shallow median concavity; frontal margin gently confluent with concave supraorbital margin; hepatic region plate-like, formed by coalesced granules; subhepatic region swollen, forming a distinct obtuse angle visible in dorsal view; hepatic plate separated from first anterolateral tooth by a wide, deep cleft; anterolateral margin with 3 large lobiform teeth increasing in size posteriorly, third tooth directed obliquely, surface paved with flattened granules, margins lined with low granules; posterolateral margin concave, with median triangular tooth, margin with rounded granules; posterior carapace margin with 2 large lozenge-shaped bosses, directed posteriorly, margin flattened, surface and margins lined with rounded and flattened granules (Figs 1 View Figure 1 , 2A-D View Figure 2 ). Suborbital region substantially compressed; subhepatic region swollen, surface with large, flattened tubercles, margins of subhepatic and pterygostomial regions covered with numerous boletiform tubercles (Fig. 3D, E View Figure 3 ); subhepatic and hepatic regions separated by distinct groove lined with granules, inner edge leading to just before tip of efferent branchial channel, outer edge joining cleft between hepatic lobe and first anterolateral tooth (Fig. 3A, B View Figure 3 ). Postfrontal median keel on gastric region prominent, high, extending posteriorly to cardiac region as raised row of rounded tubercles; postorbital region gently concave, without deep depression; median part of carapace dome-shaped, protogastric region with ovate boletiform plate, obliquely positioned, margin granulated; cardiac region swollen, with raised, vaguely T-shaped ridge formed of fused granules surrounded by rounded granules; epibranchial region with a small, subovate, transversely positioned boletiform plate, margin lined with small granules; mesobranchial region with large ovate boletiform plate, margin lined with granules; intestinal region strongly inflated, with a large subtriangular boletiform plate, directed posteriorly, margin with distinct granules (Figs 1 View Figure 1 , 2A, C, D View Figure 2 , 3A, C View Figure 3 ). Orbital margin not clearly marked, gradually merging with granules from frontal margin and hepatic region; cornea visible in dorsal view, peduncle short with small sharp granules (Fig. 2C, D View Figure 2 ). Antennule folded into an oblique fossa; basal segment finely granulate, occupying lower two-thirds of fossa (Fig. 3B View Figure 3 ). Basal antennal article large, subquadrate, fused with epistome, forming most of suborbital margin, covered with rounded tubercles; antennae small, slender, inserted in orbital hiatus (Fig. 3B View Figure 3 ). Anterior margin of efferent branchial channel produced, reaching to just before proepistome, slightly notched (Fig. 3B View Figure 3 ).

Third maxilliped with merus, ischium and exopod paved with numerous flattened, rounded tubercles of varying sizes, those on proximal parts generally larger; merus triangular, about half length of ischium; palp (carpus, propodus and dactylus) shorter than merus, inserted on inner surface; dactylus distinctly longer than propodus; ischium subrectangular, with no visible median sulcus; basis-ischium and coxa not expanded, covered with numerous large rounded tubercles and some boletiform tubercles; exopod stout, broad, reaching to about half length of merus, basal part with large rounded, boletiform tubercles (Fig. 3D, E View Figure 3 ).

Chelipeds subequal, closely covered with tubercles of varying sizes and shapes; merus trigonal in cross-section, surface covered with closely-packed low, rounded granules, posterior margin with 3 or 4 large conical tubercles, inner margin with low, broad tubercles and granules; carpus rounded, surface covered with closely-packed low, rounded granules, inner distal angle with low tooth; palm short, stout, upper and outer surfaces with low, conical tubercles, relatively densely packed, inner surface prominently swollen, covered with large, rounded granules; fingers short, shorter than palm, dorsal margin of dactylus with row of low, short granules, outer surface with low, flattened granules, cutting edge with small sharp denticles, pollex relatively broader, outer surface with small rounded granules, submarginal ones arranged in approximate rows, cutting edge with low denticles (Figs 1 View Figure 1 , 2A, B View Figure 2 , 3A, F View Figure 3 ).

Ambulatory legs short, decreasing in size posteriorly; merus, carpus and propodus covered with slender and boletiform tubercles along upper and lower margins, outer surface with large, rounded granules and tubercles; dactylo-propodal lock present; dactylus slender, glabrous, lined with granules, tip curved, corneous (Figs 2A, B View Figure 2 , 3G View Figure 3 ).

Anterior thoracic sternites (1-4) strongly compressed; sternites 1 and 2 completely fused to form small plate; sternites 3 and 4 appearing fused but vaguely demarcated by arrangement of granules, surface of sternite 3 with numerous boletiform tubercles, larger on lateral surfaces; surfaces of sternites 4-7 with flattened and low, rounded tubercles (Figs 2B View Figure 2 , 4A-D View Figure 4 ). Sternite 4 forming keel around distal part of sternopleonal cavity, occupying anterior third of overall cavity (Figs 3D View Figure 3 , 4D View Figure 4 ). Sternopleonal cavity subovate, deeply excavated, glabrous, reaching buccal cavity anteriorly; sutures between sternites 4/5, 5/6, 6/7, and 7/8 interrupted medially (Figs 3D View Figure 3 , 4D, E View Figure 4 ). Vulvae relatively small, round, positioned distinctly apart, with opening directed laterally (Fig. 4E View Figure 4 ).

Pleon ovate, shield-like, entirely covered with closely packed, rounded tubercles of varying sizes, larger ones partially coalescing; somite 1 very narrow, girdle-like, not visible when pleon closed, free; somite 2 narrow, semicircular, free; somites 3-6 completely fused, sutures not clearly visible in dorsal view, distinct in ventral view, margins lined with rounded granules; telson narrowly triangular, with proximal part broad, distal part linguiform, lateral margins deeply concave (Figs 2D View Figure 2 , 4A-C View Figure 4 ).

Remarks.

Sakai (1980: 74) described the genus and species on the basis of only one 7.0 by 5.5 mm female, and no depth information was indicated with the provenance data. The description is relatively short and only one figure was provided. The whereabouts of the holotype is not known. We have checked the various museums in Japan, Germany, Netherlands and the USA where Sakai is known to have deposited material, but we could not locate the holotype in any of these countries. Sakai (1980: 73) commented that the source of his material was from the collection of Eiji Iishiba, a member of the Japanese Carcinological Society, and it is likely that the material was returned to Iishiba after study. Where the holotype is today is not known.

At 7.8 by 6.5 mm, the present ovigerous female from Taiwan is larger than the type but closely resembles it, except that the hepatic lobe is more plate-like (Figs 1B View Figure 1 , 2A, C, D View Figure 2 ) (versus prominently granuliform); and the anterolateral lobes are more dentiform, the margins of each lobe less distinctly granuliform (Figs 1B View Figure 1 , 2A, C, D View Figure 2 ) (versus lobes more rounded and distinctly lined with rounded granules) (cf. Fig. 1A View Figure 1 ; Sakai 1980: text-fig. 1).

Not considering the generic characters, the carapace of Orientotlos iishibai superficially most closely resembles that of Alox ornatum (Ihle, 1918), which also has many rounded granules on its surface. However, in A. ornatum the granules are arranged very differently, being more closely packed and sometimes coalescing (cf. Tan and Ng 1996: pl. 5A; Galil and Ng 2007: fig. 1C; Galil and Ng 2020: fig. 1A).

No males of Orientotlos iishibai have been collected, so the important characters of the male pleon and gonopods are unknown.

Biology.

Station CP4210 is a hard bottom habitat and the trawl net was seriously damaged, though its cod end was intact. That same haul contained many sponges and crinoids and their associated fauna, including a new species of stenopodid shrimp of the genus Odontozona Holthuis, 1946, often associated with sponges (Chen and Chan, in press). The hard substrate may explain the rarity of Orientotlos iishibaii in collections, as this habitat is very hard to sample, especially in deeper waters (see Mendoza et al. 2010). In fact, the rare deep-water western Pacific leucosiid Galilia Ng & Richer de Forges, 2007 originates from a similar habitat (see Ng and Richer de Forges 2007; Komai and Tsuchida 2014; Shih et al. 2015).