Orientotlos 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

Genus Orientotlos Sakai, 1980

Type species.

Orientotlos iishibai Sakai, 1980, by original designation.

Diagnosis.

Carapace subhexagonal in outline; dorsal surfaces between plates and bosses with numerous, well-spaced boletiform and rounded tubercles; subhepatic region forming a distinct obtuse angle visible in dorsal view; hepatic plate distinct, separated from first anterolateral tooth by wide cleft; anterolateral margin with 3 large lobiform teeth; posterolateral margin concave, with median triangular tooth; posterior carapace margin with 2 large lozenge-shaped bosses; postfrontal median keel prominent, high, extending posteriorly to cardiac region as raised row of rounded tubercles; postorbital region without deep depression; large boletiform plates on protogastric, epibranchial and metabranchial regions; cardiac region with raised, vaguely T-shaped ridge formed of fused granules; intestinal region inflated, with a large subtriangular boletiform plate; antennule with basal segment occupying lower two-thirds of fossa; basal antennal article large, subquadrate, fused with epistome, forming most of suborbital margin; third maxilliped with merus, ischium and exopod paved with numerous flattened rounded tubercles, basal parts with boletiform tubercles, exopod stout, broad, reaching to about half length of merus; palm of cheliped short, stout, without ridges, lobes or teeth, fingers shorter than palm; ambulatory legs short, merus, carpus and propodus covered with slender and boletiform tubercles along upper and lower margins, dactylo-propodal lock present; anterior thoracic sternites (1-4) strongly compressed, surface of sternite 3 with numerous boletiform tubercles; female thoracic sternite 4 forming keel around distal part of sternopleonal cavity; vulvae relatively small, round, positioned distinctly apart; female pleon ovate, shield-like, covered with rounded tubercles, somites 1 and 2 free, somites 3-6 fused, telson narrowly triangular with distal part linguiform.

Remarks.

The concept of Oreophorus Rüppell, 1830 has changed substantially since 1980, with several revisions clarifying the identities of allied genera ( Tlos Adams & White, 1849, and Oreotlos Ihle, 1918) and the establishment of several new ones: Dolos Tan & Richer de Forges, 1993, Alox Tan & Ng, 1996, and Cateios Tan & Ng, 1996. Orientotlos can nevertheless be easily distinguished from these genera by the anterolateral margin of carapace not expanded posteriorly and sometimes reaching level of the posterior carapace margin, the anterolateral margin is distinctly lobiform or dentiform, dorsal carapace surface without regions distinctly raised to form bosses, with depressed areas never eroded and no obvious postocular depression or groove, cardiac region not large or strongly inflated, and the palm of cheliped is short ovate, with fingers short and relatively slender and cutting edges lined with low teeth (cf. Tan and Richer de Forges 1993; Tan and Ng 1996).

The carapace of Orientotlos only superficially resembles that of Atlantotlos (type and only species Atlantotlos rhombifer Doflein, 1904), described from off the Congo in West Africa, in general shape ( Doflein 1904: 51). The latter genus differs markedly from Orientotlos in possessing a smooth carapace, without inflated bosses, boletiform, or rounded tubercles, an entire posterior carapace margin, and less prominently armed pereopods (cf. Doflein 1904: pl. 15, figs 7, 8).

Orientotlos is actually most similar to Merocryptus A. Milne-Edwards, 1873 in having the anterolateral margin of the carapace with three large lobiform teeth (Figs 1 , 2A, C, D ) (versus margin with low lobes or spines but never clearly dentiform); a prominent lobe on posterolateral margin of carapace (Figs 1 , 2A, C, D ) (versus lobe absent or undiscernible in Merocryptus , although margin may be uneven or spiniform); median keel on gastric, cardiac and intestinal regions high and strongly inflated (Figs 1 , 2A, C, D ) (versus much lower in Merocryptus ); intestinal region formed by a pair of distinct, fused subtriangular bosses (Figs 1 , 2A, C, D ) (versus more coniform or evenly rounded in Merocryptus ); posterior carapace margin with two broad truncate, lozenge-shaped bosses (Figs 1 , 2C, D ) (versus entire or with dentiform projections in Merocryptus ); female cheliped palm and fingers proportionately shorter and stouter (Figs 1 , 2A, B , 3F ) (versus more elongate and slender in Merocryptus ); and vulvae widely spaced (Fig. 4E ) (versus proportionately larger and closer to the midline in Merocryptus ) (cf. A. Milne-Edwards 1873; Yokoya 1933; Serène 1955; Sakai 1976; Zarenkov 1994; Chen and Sun 2002; Galil 2019; Galil and Ng in press).

Figures

Figure 1. Orientotlos iishibai Sakai, 1980 A holotype female (7.0 by 5.5 mm) (repository unknown), Japan [after Sakai 1980: text-fig. 1] B color in life, female (7.8 x 6.5 mm) (NTOU B 00125), Taiwan.

Figure 2. Orientotlos iishibai Sakai, 1980, female (7.8 x 6.5 mm) (NTOU B 00125), Taiwan A overall dorsal view B overall ventral view C, D dorsal view of carapace from different angles.

Figure 3. Orientotlos iishibai Sakai, 1980, female (7.8 x 6.5 mm) (NTOU B 00125), Taiwan A frontal view of cephalothorax B frontal view showing antennules, antennae and orbits C lateral view of cephalothorax D pterygostomial region, buccal cavity, third maxillipeds and anterior part of sternopleonal cavity E left third maxilliped F outer view of left chela G right fourth ambulatory leg.

Figure 4. Orientotlos iishibai Sakai, 1980, female (7.8 x 6.5 mm) (NTOU B 00125), Taiwan A intestinal region, posterior carapace lobes and pleonal somites 2 - 6 B posterior carapace lobes, pleonal somites 2 - 6, and telson C pleonal somites 4 - 6 and telson D anterior thoracic sternites and sternopleonal cavity E sternopleonal cavity and vulvae.