Flabellamon turgidula (Alcock, 1909)

Brandis, Dirk, 2002, On the taxonomic status and biogeography of the Isolapotamidae Bott, 1970 (Decapoda, Brachyura), Journal of Natural History 36 (11), pp. 1291-1339 : 1310-1313

Flabellamon turgidula (Alcock, 1909)

(gure 10a–c)

Potamon (Potamon) turgidula Alcock, 1909: 245 ; Alcock, 1910: 42, pl. 2, gure 5.

Potamon kuehnelti Pretzmann, 1963: 363 .

Ranguna (Ranguna) turgidula: Bott, 1970b: 164 , pl. 38, gures 36, 37, pl. 51, gures 53, 54. Flabellamon pretzmanni Ng 1996: 1006 .

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Type specimens. One, one: SMF 1761, Burma, leg. W. Theobald (exch. with the Indian Museum) .

Material. One , two: MLS 1343, valley of Houngdareau (5 Haungtharaw River , at the south-west slope of the Dawna Hills , Upper Tenasserim, South Burma: 16ss36¾ 00 ² N 98ss01¾ 00 ² E) 1887, leg. Fea ; one: ZMB 8601, Meetan (5 Mitan Chaung (5river) 15ss59¾ 00 ² N 98ss24¾ 00 ² E at the south-west slope of the Dawna mountain range), leg. Fea (Holotypus of Potamon kuehnelti ); one, one: NMB 19a, Meetan, leg. Fea ; two: NMB 19b, Kokareet, Tenasserim (5 Dawna Hills) leg. Fea.

Diagnosis. Carapace smooth, lateral and frontal regions rugose; anterolateral margin well developed, serrated with equal-sized teeth, postorbital crests sharp, leading from distinct epibranchial teeth to postfrontal lobes, postfrontal lobes bulging, fused with gastric eld producing rhombi-like structure; chelae more or less equal, closing entire cutting edge; pleon slender, triangular, slightly concave. Terminal joint of rst gonopod with disk-like mesial bulging of overlapping zone, exible zone broad, with one median, elongated lobe.

Type locality. Tenasserim , Burma .

Distribution. West slope of Dawna hills.

Remarks. Until now there has been a great deal of confusion concerning the distribution and taxonomy of this species, which is attributable to several facts: all available material is very old (19th century to beginning of 20th century), discrepancies in the descriptions published by Alcock (1909, 1910) and the unspeci c type locality (‘Burma’). DiOEerent spellings of localities (e.g. Meetun–Meelan–Mitan) and unclear old records also contributed to this confusion. Alcock (1909) described the species on the base of 11 males and two females with the locality ‘Burma’ collected by W. Theobald. These specimens are catalogued under the number 6952/ 3 in the Zoological Survey of India. Alcock described P. turgidulum as a small species similar to P. tumidum . According to Alcock (1909, 1910) the following features are characteristic for P. turgidulum :

length of the carapace in adults being less than an inch;

the indistinct and super cial carapacial grooves;

the convex carapace;

the narrow front with a bilobed edge;

the second pair of legs being considerably longer than the chelipeds; epigastric crests separated from postorbital crests by an indistinct groove, forming ‘the convexity of a common curve with them’.

He gured one specimen in his revision of the Indian Potamidae (1910) . Bott (1970b) examined two specimens from the Senckenberg collections (SMF 1761) and from the Natural History Museum Basel (NMB 19a, b) for his revision and assigned both to P. turgidulum . Ng (1996) pointed out that the specimen gured by Alcock (1910) and which he believed belonged to the type series diOEered from that of Bott (1970b). He thus assigned specimens from the NRC ( Singapore) that were similar to those of Bott to a new species, F. pretzmanni Ng, 1996 .

In fact, it seems that Alcock’s type series consisted of at least two species. This can already be seen from discrepancies in the original description of 1909 when compared with the gure published in 1910. The detailed description in the 1910 volume further supports this conclusion: Alcock (1910) described the epigastric crests as separated from the postorbital crests by an indistinct groove, forming ‘the convexity of a common curve with them’. The gure of Alcock shows epigastric and postorbital crests which are distinctly concave and not all convex. I examined part of the type series, i.e. 2 (SMF 1761), which were examined by Bott (1970b), 1 (NHM 1909.5.1.8.) and 1 (USNM 42774), all exchanged or presented by the

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Zoological Survey of India (ZSM 6952/3). This material con rms the heterogeneity of the type series, because SMF 1761 agrees with Alcock’s description cited above, while the two females look like his 1910 gure. This means that the name Potamon turgidulum, Alcock, 1909 could be either applied to the species described by Ng (1996) under the name F. pretzmanni , the identity of which does not pose any problems, or the gured specimen, of which the identity is totally unclear, even at the level of family assignment. It could be a Potamid, an Isolapotamid or a Sinopotamid. As I have no access to the male specimen gured by Alcock (1910) and as the two female syntypes (NHM 1909.5.1.8. and USNM 42774) do not help in the solution of this problem the identity of this form remains dubious. I, therefore, prefer to use Alcock’s P. turgidulum in the sense of F. pretzmanni , which has the consequence of the synonymy of both. By this action it can be avoided that a dubious name would oat around and form a potential threat for any name of species of this area. When the male specimen in the Zoological Survey of India becomes available, it can then either be identi ed with another described species, or be given a new name. In any case this is in my opinion the best solution for the stability of nomenclature.

One small specimen from the Kokareet/Dawna mountains (NMB 19b) shows a mesial disc-like projection of the rst gonopod terminal joint, which is narrower than that of the larger male specimen of the same sample and that of the specimens from Mitan (NMB 19a) and the Haungtharaw river (MLS 1343). This narrowing of the projection of the single small specimen from the Dawna mountains (NMB 19b) already mentioned by Bott (1970b) and Ng (1996) is not enough of a diOEerence to establish a distinct species, mainly because the other specimen from the same sample shows the same large disc-like projection as all other examined specimens of this species. Most probably, the smaller specimen is subadult and the structural diOEerence of the rst gonopod is caused by growth and maturation eOEects. Additionally, larger series from the Dawna hills are lacking and a more detailed study of the morphologic variation of the rst gonopod is presently not possible. Thus, this diOEerence should not be used at present to split oOE another species until more abundant material from this region becomes available. Finally, the comparison of the rst gonopods of F. turgidula and P. kuehnelti shows that both are morphologically completely identical. Therefore, based on available material, F. turgidula is the only valid species, while P. kuehnelti and F. pretzmanni are here treated as junior synonyms of F. turgidula .

The zoogeography of this species is interesting. It is so far known only from the western and southern slopes of the Dawna hills, which means that it could be endemic in this region.