PRELIMINARYDESCRIPTIONSOF ONE NEW GENUS AND
THREE NEW SPECIES OF HYMENOSOMATID
CRABS FROM
SOUTHEAST ASIA (CRUSTACEA: DECAPODA: BRACHYURA)

ABSTRACT. - Preliminary descriptions are provided for one new genus and three new speciesof Southeast Asian hymenosomatids -Limnopilos naiyanetri, new genus and species (Thailand);Elamena glohosa, new species, and Elamena mendosa, new species (both from Singapore).
Limnopilos is the second freshwater hymenosomatid known from Southeast Asia, and the firstfrom Thailand.

Lucas (1980) in his revision of the Australian Hymenosomatidae, commented that thehymenosomatid fauna of Southeast Asia is poorly studied and indicated that many more taxa
probably still await discovery. Compared to the 29 species known from Australia, only sevenspecies have been reported from Southeast Asia - Elamena sindensis Alcock, 1896 (Singapore,fide Yang, 1979), Halicarcinus coralicola (Rathbun, 1909) (Singapore, Thailand, fide Rathbun,1909; Naiyanetr, 1980), Trigonoplax unguiformis (de Haan, 1839) (Singapore, fide Lanchester,1900); Elamenopsis exigua (Kemp, 1917) (Thailand, fide Kemp, 1917), Elamenopsis palawanensis Serene, 1971 (Palawan, fide Serene, 1971; Lucas, 1980), Elamenopsis mangalis Ng,1988 (Singapore, fide Ng, 1988), and Cancrocaeca xenomorpha Ng, 1991 (Sulawesi, fide Ng,1991).
A study of the Hymenosomatidae in the collection of the Zoological Reference Collection(ZRC), Department of Zoology, National University of Singapore, shows that the hymenosomatid fauna of Southeast Asia is more diverse than previously believed. Two of the old records
from Singapore proved to be incorrect: the material reported as Elamena sindensis is actually
Elamenopsis mangalis; whereas Trigonoplax unguiformes is an undescribed speciesof Elamena,
here named E. mendosa, new species. The second known Southeast Asian freshwater hymenosomatid is described from Thailand - Limnopilos naiyanetri, new genus and species. A newspecies of Elamena, E. glohosa, with the most swollen carapace known thus far for any
hymenosomatid, is also described from sublittoral waters in Singapore.

Christina T. N. Chuang, Peter K. L. Ng - Department of Zoology, National University ofSingapore, Kent Ridge, Singapore 0511, Republic of Singapore.

As the names of some of these new taxa are needed for other reports and studies currently
under preparation, preliminary diagnoses are provided for the new genus and three new species
to faciliate the usage of the names. The detailed taxonomic account of the nine known species
from Southeast Asia, including redescriptions of poorly known taxa (e.g. Halicarcinus
coralicola and Elamenopsis palawanensis), new records etc., will be published at a later date.
Measurements, in milimetres, are of. the carapace width and length respectively. The
terminology used here follows that by Melrose (1975) and Lucas (1980). Specimens aredeposited in the ZRC; Reference Collection of the Chulalongkorn University (CNHM),Bangkok, Thailand; and the Rijksmuseum van Natuurlijke Historie (RMNH), Leiden,Netherlands.

Diagnosis. - Rostrum of carapace absent, Milne Edwards openings with more than two thirds
fused grooves and margin. Distal portion of chela with dense setae on upper and lower margins.
All male and female abdominal segments free.
Etymology. - The genus name Limnopilos is an arbitary combination of letters with a vague
reference to the fact that the animals of this genus inhabit fresh water and are hairy. The genderof Limnopilos is masculine.
Remarks. - The absence of a rostrum is an unusual feature in hymenosomatids, and allies
Limnopilos with the monotypic genera Hymenicoides Kemp, 1917, and Halicarcinides Lucas,
1980. Other than in having no rostrum however, Limnopilos naiyanetri differs from Hymenicoides carteri Kemp, 1917, in that its telson is not trilobate and the male first pleopods aresimpler in structure. Limnopilos differs from Halicarcinides nuytsi (Hale, 1927) in that the eyes
are not concealed by the anterior part ofthe carapace (from dorsal view), carapace shape, shorter
epistome and different male first pleopod structure. Limnopilos also resembles the genus
Elamenopsis A. Milne Edwards, 1873, sensu Lucas, 1980, in having well defined carapace
grooves and narrow third maxillipeds, but differs very significantly in not having a rostrum, thehighly setose body and the male and female abdominal segments are all free (not with somesegments fused). A new genus thus has to be established for naiyanetri new species.

Limnopilos naiyanetri, new species(Fig. 1)
Material examined. - Holotype - 1 male, 6.0 by 5.9 mm (ZRC), Mae Nam Nakhon Chaisi,
Amphoe Nakhom Chaisi, Changwat Province, Nakhom Pathom, leg. Naunsri, 1988.
Paratypes - 24 males, 13 females (ZRC), 5 males, 5 females (CNHM), 10 males, 2 females(RMNH), same data as holotype.

Diagnosis. - Carapace flat with distinct contiguous gastro-cardiac grooves and margin;
rostrum absent. Chela with dense setae on upper and lower margins of distal portion; propodus
with row of setae on inner edge 1.6 times longer than those on upper margin; distal part ofimmovable finger with four teeth, ending in a facet; dactylus with a tooth on medial proximalportion; carpus with two marginal teeth; merus with a tooth on medial lower edge. All male andfemale abdominal segments free.
Etymology. - The species is named in honour of Professor Phaibul Naiyanetr of theDepartment of Biology, Chulalongkom University, Bangkok, Thailand, who has made many
outstanding contributions to Thai carcinology, helped the second author on so many occasions
over the years and kindly referred the present specimens to the authors for study.
Remarks. - This very unusual species is characterised by its pilose carapace and chelipeds,
and this respect, resembles Amarinus pilosus (A. Milne Edwards, 1873) from New Caledonia(see also Holthuis, 1968). It differs however significantly in the absence of a rostrum, andstructures of the male abdomen and male first pleopod.

Fig. I. Limnopilos naiyanetri, new genus, new species. a, dorsal surface of carapace; b, left cheliped; c,left third maxilliped; d, right second walking leg.

Elamena globosa, new species(Fig.2a-d)Material examined. - Holotype - 1 male, 2.2 by 2.65 mm (ZRC), Pulau Ayer Chaw an island,
southern Singapore, leg. Reef Ecology Team, 1986.
Diagnosis. - Carapace approximately circular, lateral carapace margin without spines; dorsal
surface highly convex, appears inflated, with faint grooves; rostrum triangular, not concealing
antennae, antennules and most of the eyes; medial ridge running from tip of rostrum to base ofcarapace. Male first pleopod with a distinct double twist. Third and fourth male abdominal
segments fused, without distinct sutures, other segments free.

Remarks. - Elamena globosa, new species, is the most globose species ofhymenosomatid yetknown, and this feature will easily serve to distinguish it from all others. The male first pleopod
has a very distinctive double twist, a feature shared by few other hymenosomatids, e.g.
Cancrocaeca xenomorpha Ng, 1991 (see Ng, 1991).

Elamena mendosa, new species(Fig.2e-g)
Material examined. - Holotype - 1 male, 2.2 by 2.65 mm (ZRC), Sisters Islands, southern
Singapore, leg. 1985.

Diagnosis. - Carapace approximately triangular; dorsal surface slightly convex, with nodistinct grooves; rostrum triangular, slightly upturned, with rounded apex, without keel on theventral surface, concealing antennae, antennules and most of the eyes. Male and female fifth
segment and telson fused, sutures not visible, all other male and female abdominal segments
free.
Etymology. - The species name is derived from the Latin "mendosus" which means faulty,
wrong or mistaken; alluding to the long mistaken identity of the crab.
Remarks. - Lanchester (1900) identified a female specimen from Singapore as Trigonoplax
unguiformes (de Haan, 1839). This record has since been cited by subsequent workers like Tesch(1918), Sakai (1976) and Lucas (1980). Specimens obtained from Singapore waters show thatwhile these resemble T. unguiformes s. str. superficially, the shape of the carapace, rostrum andMilne Edwards openings showed obvious and constant differences. These differences necesssitate the establishment of a new taxon for the Singapore specimens. The Milne Edwards openingsof E. mendosa are also fused for only less than one third of their length, the main character citedby Lucas (1980) for separating Trigonoplax from Elamena (the openings are fused for morethan half its length in Trigonoplax).

Fig. 2. a-d, Elamena globosa new species. a, dorsal surface of carapace; b, lateral view of carapace; c, left
third maxilliped; d, right third walking leg. e-g, Elamena mendosa new species. e, dorsal view of carapace;f, left third maxilliped; g, right walking leg.

Acknowledgements. - The authors are most grateful to Professor Phaibul Naiyanetr (Chulalongkom University, Bangkok) for passing us the Thai freshwater hymenosomatids for study.
Prof. L. B. Holthuis kindly read through and reviewed the manuscript; his comments andrecommendations being much appreciated. One of the specimens (Elamena globosa) wasobtained by the "ASEAN-Australia Marine Science Project: Living Coastal Resources" team.
Thanks are also due to our friends in the Reef Ecology Laboratory, National University ofSingapore, for their kind assistance. The specimens in the ZRC were examined through thecourtesy of Mrs. C. M. Yang. Prof. Holthuis also sent us some material in the RMNH. Dr. ChouLoke Ming provided equipment, laboratory space and help to the first author on severaloccasions for which she is grateful. This study has been partially supported by a National
University of Singapore Research Grant RP 900360 to the second author.

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Kemp, S., 1917. Notes on Crustacea Decapoda in the Indian Museum. X. Hymenosomatidae.
Mus., 13: 243-279.

Rec./nd.

Lanchester, W. F., 1900. On a collection of crustacea made at Singapore and Malacca.-Part I. CrustaceaBrachyura. Proc. Zool. Soc. Lond., 1900: 719-770, Pis. 44-47.
Lucas, J. S., 1980. Spider crabs of the family Hymenosomatidae (Crustacea; Brachyura) with particularreference to Australian species: systematics and biology. Rec. Australian Mus., Sydney, 33(4): 148-247.
Melrose, M. J., 1975. The Marine fauna of New Zealand: Family Hymenosomatidae
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Biology, Fac. Sci., Chulalongkom Univ. Bangkok, 73 pp. (mimeographed).

(Crustacea,Department ofNg, P. K. L., 1988. Elamenopsis mangalis sp. nov., a new species of mangrove-dwelling hymenosomatid
crab from Singapore (Crustacea, Decapoda, Brachyura). Crustaceana, Leiden, 55(3): 274-278.
Ng, P. K. L., 1991. Cancrocaeca xenomOlpha, new genus and species, a blind troglobitic freshwater
hymenosomatid (Crustacea: Decapoda: Brachyura) from Sulawesi, Indonesia. Raffles Bull. Zool., Singapore,39(1): 59-63.

Sakai, T., 1976. Crabs of Japan and the Adjacent Seas. In three volumes; English Text, pp. xxix + 773pp.,
Japanese Text, pp. 1-461, Plates Volume, pp. 1-16, Pis. 1-251. Kodansha Ltd., Tokyo.
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Tesch, T. T., 1918. The Decapoda Brachyura of the Siboga Expedition. I. Hymenosomidae, Retrop1umidae, Ocypodidae, Grapsidae and Gecarcinidae. Siboga Exped., 39c(82): 1-148, 6 Pis.
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