Research Article |
Corresponding author: Tin-Yam Chan ( tychan@mail.ntou.edu.tw ) Academic editor: Sameer Pati
© 2021 Peter K. L. Ng, Tin-Yam Chan.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Ng PKL, Chan T-Y (2021) Rediscovery of Orientotlos iishibai Sakai, 1980 (Crustacea, Decapoda, Brachyura, Leucosiidae) in Taiwan. ZooKeys 1053: 185-195. https://doi.org/10.3897/zookeys.1053.67326
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The leucosiid crab Orientotlos iishibai Sakai, 1980 was described from one female collected off western Japan and had never been reported since. The species is now recorded from southwestern Taiwan for the first time, and is redescribed and figured at length. Although Sakai argued that Orientotlos Sakai, 1980, is closely related to Oreophorus Rüppell, 1830 and Atlantotlos Doflein, 1904, the genus is actually morphologically most similar to Merocryptus A. Milne-Edwards, 1873. The two genera, however, still differ markedly in a number of key carapace and cheliped characters.
East Asia, Leucosioidea, new record, redescription, rubble crab, taxonomy
The terminology used follows
Orientotlos iishibai Sakai, 1980, by original designation.
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.
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.
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 (
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
Orientotlos iishibai
Sakai, 1980: 74, text-fig. 1. –
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;
As for genus.
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
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.
Orientotlos iishibai Sakai, 1980, female (7.8 × 6.5 mm) (
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
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
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
Orientotlos iishibai Sakai, 1980, female (7.8 × 6.5 mm) (
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
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
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.
No males of Orientotlos iishibai have been collected, so the important characters of the male pleon and gonopods are unknown.
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
Sincerely thanks are extended to Tohru Naruse and an anonymous reviewer for providing constructive comments. This work was supported by research grants from the Ministry of Science and Technology, Taiwan and the Center of Excellence for the Oceans (National Taiwan Ocean University), which is financially supported from the Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan.