Oreotlos latus (Borradaile, 1903), a new record for Taiwan, with the first description of a male and...

OREOTLOS LATUS (BORRADAILE, 1903), A NEW RECORD FOR TAIWAN,WITH THE FIRST DESCRIPTION OF A MALE AND A REVISED KEY TO

THE GENUS (BRACHYURA, LEUCOSIIDAE)

BY

NGAN KEE NG1,4), PAN-WEN HSUEH2,5) and PETER K. L. NG3,6)1) Department of Biological Science, National University of Singapore, Kent Ridge,

Singapore 119260, Republic of Singapore2) Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan 402, R.O.C.

3) Tropical Marine Science Institute, 14 Kent Ridge Road, Singapore 119223,Republic of Singapore

ABSTRACT

The poorly known leucosiid crab, Oreotlos latus (Borradaile, 1903) is reported for the first timefrom Taiwan. Only three female specimens, including the holotype, were previously known, i.e.,from the Maldives, Eniwetok, and Japan. The present specimen is the first male known and itscharacters are described and figured. A revised key to Oreotlos Ihle, 1918, is also provided.

RÉSUMÉ

Le crabe Leucosiidae peu connu, Oreotlos latus (Borradaile, 1903) est signalé pour la premièrefois de Taiwan. Seuls, trois spécimens femelles, dont l’holotype, étaient auparavant connus, desMaldives, de l’atoll d’Enewetak et du Japon. Le présent spécimen est le premier mâle connu etses caractères sont décrits et figurés. Une clé révisée des espèces du genre Oreotlos Ihle, 1918, estégalement donnée.

INTRODUCTION

Recently, an extraordinary leucosiid crab, Oreotlos latus (Borradaile, 1903), wascollected from an intertidal coral reef habitat in southern Taiwan. The species wasoriginally described from one female from the Maldives by Boradaile (1903) andwas subsequently reported from the Andaman Islands (Sankarakunthy, 1962), the

4) e-mail: [email protected]) Corresponding author; e-mail: [email protected]) e-mail: [email protected]

© Koninklijke Brill NV, Leiden, 2009 Crustaceana 82 (6): 679-688Also available online: www.brill.nl/cr DOI:10.1163/156854009X404798

680 N. K. NG, P.-W. HSUEH & P. K. L. NG

Malay Archipelago and the Philippines (Ihle, 1918), Japan (Takeda, 1977; Miyake,1983; Nagai & Nomura, 1988), and Hawaii (Rathbun, 1906; Edmondson, 1925).However, all these records were referred to other species (see Tan & Ng, 1995). Thespecimen reported in the present study is only the fourth known for the species, andthe first male ever collected.

The present study describes the male characters of O. latus for the first time,and formally reports it from Taiwan. Some aspects of the taxonomy of thespecies and genus are discussed and a revised key to the species of Oreotlos ispresented. The specimen is deposited in the Zoological Reference Collection ofthe Raffles Museum of Biodiversity Research, National University of Singapore.The terminology used follows Tan & Ng (1995) and the abbreviations G1 andG2 are used for the male first and second pleopods, respectively. Measurementsprovided, in millimeters, are of the carapace width and length, respectively.

TAXONOMY

Family LEUCOSIIDAE Samouelle, 1819

Oreotlos Ihle, 1918

Oreotlos latus (Borradaile, 1903)(figs. 1-3)

Tlos latus Borradaile, 1903: 437, fig. 15.Oreophorus (Oreotlos) latus — Miyake, 1983: 201.Oreophorus (Oreophorus) latus — Nagai & Nomura, 1988: 121.Oreotlos latus — Tan & Ng, 1995: 155, fig. 23, pls. 14E, F, 15A; Ng et al., 2008: 92.

Material examined. — Male (5.1 × 4.4 mm) (ZRC), Wunlitung (21◦59.44′N, 121◦42.16′E),Pintung County, Taiwan, among coral rubble, lower intertidal zone, coll. P.-W. Hsueh, 13 March2008.

Description. — Carapace ca. 1.9 times as broad as long. Margins of cara-pace with rim, granulated. Regions not clearly defined; dorsal surface coveredwith small, flat granules, barely visible to the naked eye; with shallow, irregularlyshaped grooves and circular depressions; prominent granule on dorsal surface pos-terior to hepatic angle. Margin of hepatic region beaded, protruding slightly toform obtuse angle; margin of subhepatic region protruded to form obtuse angle,with larger granules at tip; deep, oblique, granulated groove present on ventral sur-face posterior to subhepatic angle. Frontal margin granulated, produced forward,bilobed, entire, lateral edges effectively confluent with supraorbital margin; supra-orbital margins entire, strongly deflected downwards, forming prominent crimp atjunction between frontal and supraorbital margins. Triangular depression presenton postorbital region. Median longitudinal ridge on carapace distinct, very wide.

OREOTLOS LATUS (BORRADAILE) IN TAIWAN 681

Branchial regions swollen, with short, transverse row of larger granules betweenthem; shallow, irregularly shaped groove present on either side of cardiac and in-testinal regions; branchiostegal region finely granulated, with no distinct granu-lated region. Anterolateral margin faintly trilobed, lobes separated by very broad,shallow clefts; external orbital (first) lobe most distinct, broad; second lobe verybroad, third lobe very low, just discernible. Posterolateral margin not sharply de-marcated from anterolateral margin, appearing almost straight, distinctly converg-ing towards true posterior carapace margin but demarcated from it by a small notch.Posterior carapace margin entire, sinuous (figs. 1A, 2A). Orbits small, entire, eyesnot completely filling orbit, cornea well developed. Pterygostomial, suborbital, andbranchial regions granulated. Basal segment of antennule occupies about half offossa, folding obliquely when closed; margin of fossa lined with granules.

Third maxillipeds covered with fine granules as on carapace; merus narrowlytriangular with pointed apex, middle of anterolateral margin with group of granulesforming a slight angle. Ischium about 2 times as long as merus along innermargin, distinctly longer than broad, proximal third of inner edge lined by largegranules, no sulcus present. No gape formed between inner margins of meriand ischia of third maxillipeds when closed. Carpus of palp much wider thanrest of structure (propodus and dactylus). Exopod covered with granules, obtuse,with blunt inner subdistal angle covered with several long, soft, simple setae, noflagellum discernible (fig. 2B).

Chelae small, equal. Outer surfaces of meri and carpi covered with small roundgranules (figs. 1A, 3A–E), all margins with large, rounded granules. Outer surfaceof cheliped with low granules towards proximal end (fig. 3D); inner surface ofcheliped covered with small rounded granules reaching base (fig. 3E); inner dorsalsurface of palm with 3 large granules near proximal end. Fingers distinctly 1.5times as long as palm; distal half of cutting edges of both fingers with small,denticulate teeth, ending in small, recurved, sharp tips; no gape discernible whenfingers closed.

Ambulatory legs with first pair the longest (fig. 1A). Anterior margin of merusof third and fourth pairs of ambulatory legs (figs. 2D, E) lined with small granuleson proximal part, posterior margin with large granules near proximal part; anteriorregion of carpus covered with rounded granules; anterior and posterior marginsof propodus with large, sharp granules; dactylus long, narrow, covered with smallsharp granules, dactylus ending in sharp corneous tip.

Male abdomen narrowly triangular, covered with small granules and depres-sions as on carapace (fig. 3G); lateral margins sparsely setose. Somite 1 weaklyarched, with weak transverse ridge, usually covered by the posterior carapace.Somite 2 relatively broad, proximal margin with 1 median lobe and 2 smallerlateral lobes, median lobe with large, rounded granules. Somites 3-5 completely


Fig. 1. Oreotlos latus (Borradaile, 1903). Male (5.1 × 4.4 mm) (ZRC). A, dorsal view; B, frontalview; C, ventral view.


Fig. 2. Oreotlos latus (Borradaile, 1903). Male (5.1 × 4.4 mm) (ZRC). A, carapace; B, thirdmaxilliped; C, frontal view of face; D, last ambulatory leg; E, third ambulatory leg. Scale = 1.0 mm.


Fig. 3. Oreotlos latus (Borradaile, 1903). Male (5.1 × 4.4 mm) (ZRC). A, outer view of cheliped;B, outer view of chela carpus; C, outer view of chela merus; D, inner view of cheliped; E, top viewof carpus and cheliped; F, sternum; G, abdomen; H, different views of G1; I, different views of G2.

Scale = 1.0 mm.


fused, lateral margins with 2 shallow depressions indicating end of each somite;somite 3 with proximal margin somewhat trilobed, a small tubercle present slightlybelow each lateral lobe, with a small rounded tubercle medially; a large roundedmedian tubercle is present on depressed part of somites 4 and 5; somite 5 withdistal margin sinuous, lateral regions slightly convex. Somite 6 subquadrate, lat-eral margins converging, weakly convex, proximal margin slightly concave, con-vex medially, distal margin concave. Telson narrowly triangular, proximal marginweakly convex, lateral margins weakly convex, distal margin pointed.

Thoracic sternum with all margins granulated (fig. 3F). Sternite 1 triangularin shape, small. Sternites 2 and 3 separated by partial suture. Sternites 4 and 5without clear suture except for notches present on lateral margins. Sutures betweensternites 5 and 6, sternites 6 and 7, and sternites 7 and 8 distinct medially. Sternite7 broadest, sternite 8 smallest, Abdominal cavity relatively broad, extendinganteriorly slightly beyond anterior margin of sternite 3.

Penis located at base of thoracic sternite 8 (fig. 3F). G1 slender, almost straight;distal part tapering, weakly curving outwards, reaching to anterior margin of fifthsternite (fig. 3G). G2 short, small, slender, apex elongate (fig. 3H).

Remarks. — The species has a somewhat confused taxonomic history until Tan& Ng (1995) revised it. They referred previous records of “O. latus” from theMalay Archipelago and Philippines by Ihle (1918), and from Japan by Takeda(1977), to O. heuretos Tan & Ng, 1995; from Hawaii by Rathbun (1906) andEdmondson (1925) to O. lagarodes Tan & Ng, 1995; and from the Andaman andNicobar Islands by Sankarakunthy (1962) to Alox latusoides (Sakai, 1937).

Of the 12 species of Oreotlos recognized at present (Tan & Ng, 1995; Ng et al.,2008), O. latus most closely resembles O. lagarodes Tan & Ng, 1995 superficiallyin its external appearance. However, O. latus can easily be distinguished by thepresence of wrinkle-like grooves on the carapace (versus pits), a more producedfront, and possessing relatively stouter chelipeds. The present male of O. latusadds new differences between the two species: the male abdomen of O. latus ismore quadrate than that of O. lagarodes, with the fused somites 3-5 rectangular inshape (vs. triangular) and somite 6 and the telson proportionately broader (fig. 3Gherein vs. Tan & Ng, 1995, fig. 22C); the G1 is more slender and proportionatelymuch longer (fig. 3H herein vs. Tan & Ng, 1995, fig. 22D); and the G2 is relativelyshorter (fig. 3H herein vs. Tan & Ng, 1995, fig. 22E).

The type locality of O. latus is in the Maldives Islands in the Indian Ocean,but it is also known from Eniwetok in the Marshall Islands, and Okinawa inJapan (Tan & Ng, 1995). The discovery of this species in Taiwan is, therefore,not surprising. Richard Barnes (pers. comm.) recently showed the third author anexcellent photograph of a living specimen clearly referable to O. latus obtained


from the Maldives. Unfortunately, it was not collected and it was not possible toascertain its sex. Its colour in life was creamy white.

More significantly, the present specimen of O. latus is a male, all previousmaterial having been represented by females. A prominent tubercle is presentmedially on the fused male abdominal somites 3-5, a character that Tan & Ng(1995) have commented to be diagnostic for Oreotlos, separating it from alliedgenera.

The key provided in Tan & Ng (1995: 141) for Oreotlos missed O. lagarodes.A revised key is presented below, which not only includes O. lagarodes but alsoallows us to update some of the characters used.

KEY TO THE SPECIES OF OREOTLOS

1a. Lateral expansions of carapace plate-like, edge relatively thin; concave on dorsal surface, withno distinct depressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1b. Lateral expansions of carapace thick, flat, edge thick; distinct depressions may be present ondorsal surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2a. Branchial regions convex, smooth; posterolateral margins upturned, forming 2 triangular ridgesthat are flattened dorsally to form plateau-like structure, ridges connected by central transverseridge; region posterior to plateau-like structure prominently concave with sloping sides . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. havelocki (Laurie, 1906)

2b. Branchial regions swollen; posterolateral margins not upturned, no plateau-like triangularstructure evident; region posterior to branchial regions not concave, sides slightly sloping . . . 3

3a. Carapace heart-shaped, about 1.4 times as broad as long; branchial regions relatively flat, finelygranulated; margins of hepatic and subhepatic regions only slightly convex; grooves on eitherside of intestinal region shallow, indistinct . . . . . . . . . . . . O. etor Tan & Richer de Forges, 1993

3b. Carapace transversely ovate, about 1.6 times as broad as long; branchial regions raised,coarsely granulated; margins of hepatic and subhepatic regions produced to form angles, withsubhepatic angle very prominent, pointed; grooves on either side of intestinal region deep,distinct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .O. potanus Tan & Richer de Forges, 1993

4a. Carapace broadly ovoid/rectangular; anterolateral margins nearly parallel to posterolateralmargins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4b. Carapace pentagonal; anterolateral margins and/or posterolateral margins positioned obliquelyto each other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5a. Lateral expansions of carapace with 3 moderately deep depressions on either side, whichincrease in size (from posterior-most depression onward); branchial regions appear very flatwhen viewed frontally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. pala Tan & Ng, 1995

5b. Lateral expansions of carapace with small, shallow, irregular depressions or pits, and/orwrinkle-like grooves; branchial regions appear moderately flat when viewed frontally. . . . . . .6

6a. Front relatively more produced anteriorly; carapace more rounded, less angular in shape; dorsalsurface of carapace pitted; chelipeds relatively stouter, ratio of fingers to palm 1.5; G1 veryslender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. latus (Borradaile, 1903)

6b. Front relatively more produced anteriorly; carapace more rounded, less angular in shape; dorsalsurface of carapace pitted; chelipeds relatively stouter, ratio of fingers to palm 1.6; G1 relativelystout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. lagarodes Tan & Ng, 1995

7a. Dorsal surface of carapace finely granular with a few scattered, larger granules . . . . . . . . . . . . . 8


7b. Dorsal surface of carapace coarsely granular with scattered clumps of large granules . . . . . . . 9

8a. Front with deep median cleft; carapace 1.3 times as broad as long; lateral margins of carapacedivided into 3 broad lobes on each side by 2 clefts; cutting edges of fingers of cheliped withlong narrow teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .O. bertrandi Tan & Ng, 1995

8b. Front without deep median cleft; carapace 1.5-1.6 times as broad as long; lateral margins ofcarapace entire; cutting edges of fingers of cheliped with broad triangular teeth . . . . . . . . . . . 10

9a. Front strongly produced beyond eyes; branchial regions with distinct, inverted “Y”-shapedgranular ridge; prominent clump of granules present immediately after hepatic angle . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. encymus Tan & Ng, 1993

9b. Front slightly produced beyond eyes; branchial regions with irregularly shaped clumps ofgranules; large prominent granule present immediately after hepatic angle . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O. angulatus (Rathbun, 1906)

10a. Front entire, squarish; carapace margins lined with small sharp granules, giving it angularappearance; fingers of cheliped relatively narrow . . . . . . . . . . . . . . . . . . O. speciosus Chen, 1989

10b. Front bilobed, rounded; carapace margins lined with rounded granules, giving it more roundedappearance; fingers of cheliped relatively stout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

11a. Carpus of third maxilliped palp equal in size and width to propodus and dactylus; surface offemale abdomen without distinct grooves on either side of median line; G1 2.1 times as longas G2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .O. pax Tan & Ng, 1995

11b. Carpus of third maxilliped palp about twice size and width of propodus and dactylus; surfaceof female abdomen with distinct grooves on either side of median line; G1 2.4 times as long asG2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .O. heuretos Tan & Ng, 1995

ACKNOWLEDGMENTS

This study is supported by a grant (NSC95-2621-B-005-011-MY3) from theNational Science Council, Taiwan, R.O.C. to PWH. Tranh Anh Duc kindlyphotographed the specimen. We thank Richard Barnes for sharing with us hisphotograph of O. latus.

REFERENCES

BORRADAILE, L. A., 1903. Marine crustaceans, VI. The sand crabs (Oxystomata). In: J. S. GARD-NER (ed.), Fauna and geography of Maldives and Laccadives Archipelagos, being the accountof the work carried on and of the collections made by an expedition during the years 1899-1900: 1-754, pls. XXII-LVIII.

EDMONDSON, C. H., 1925. Crustacea. Marine zoology of the tropical central Pacific. Bull. BerniceP. Bishop Mus., 27: 3-62, pls. 1-4.

IHLE, J. E. W., 1918. Die Decapoda Brachyura der Siboga-Expedition, 3. Oxystoma: Calappidae,Leucosidae, Rannidae. Siboga Exped. Monogr., 39b2: 159-322.

MIYAKE, S., 1983. Brachyura (crabs). Japanese crustacean decapods and stomatopods in color, 2:1-277, pls. 1-64, unnumbered figs. (Hiokusha, Osaka).

NAGAI, S. & K. NOMURA, 1988. The guide book of Okinawan marine organisms, 7, Crustacea(Brachyura): 1-250. (Shinshei Tosho, Okinawa).

NG, P. K. L., D. GUINOT & P. J. F. DAVIE, 2008. Systema Brachyurorum: Part I. An annotatedchecklist of extant brachyuran crabs of the world. Raffles Bull. Zool., (Suppl.) 17: 1-286.


RATHBUN, M. J., 1906. The Brachyura and Macrura of the Hawaii Islands. U.S. Fish. Comm. Bull.,3: 827-930, pls. 1-24.

SAKAI, T., 1937. Studies on the crabs of Japan, II. Oxystomata. Sci. Rep. Tokyo Bun. Daig., (B)(Supplement) 2-3: 67-192, pls. 10-19.

SAMOUELLE, G., 1819. The entomologist’s useful compendium, or an introduction to the knowl-edge of British insects: 1-469, pls. 1-12. (Thomas, London).

SANKARAKUNTHY, C., 1962. On Decapoda Brachyua from the Andaman and Nicobar Islands. 3.Families: Calappidae, Leucosiidae, Parthenopidae, Majidae, and Geocarcinidae. Journ. mar.biol. Ass. India, 4(1): 151-164.

TAKEDA, M., 1977. Crabs of the Ogasawara Islands, V. A collection made by dredging. Mem. natn.Sci. Mus., Tokyo, 10: 113-140, pls. 12-17.

TAN, C. G. S. & P. K. L. NG, 1995. A revision of the Indo-Pacific genus Oreophorus Rüppell,1830 (Crustacea: Decapoda: Brachyura: Leucosiidae). In: B. RICHER DE FORGES (ed.), Lesfonds meubles des lagons de Nouvelle-Calédonie (sédimentologie, benthos): 101-189. (Étudeset Thèses, 2, ORSTOM, Paris).

First received 24 May 2008.Final version accepted 5 August 2008.

Oreotlos latus (Borradaile, 1903), a new record for Taiwan, with the first description of a male and...

Documents

Transcript of Oreotlos latus (Borradaile, 1903), a new record for Taiwan, with the first description of a male and...