Demanietta Bott, 1966

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 : 1304-1308

Demanietta Bott, 1966

(gures 4a, 7, 8)

Potamiscus (Demanietta) Bott, 1966: 487 .

Ranguna (Demanietta) : Bott, 1970b: 173.

Demanietta: Naiyanetr, 1992a: 113 ; Ng and Naiyanetr, 1993: 33.

Thaiphusa Ng and Naiyanetr, 1993: 31 ; Yeo et al., 1999: 531.

Type species. Potamon (Potamon) manii Rathbun, 1904 [by original designation]. Diagnosis. Terminal joint of rst gonopod shorter than subterminal joint;

S-shaped, overlapping margin reaching mesial side, margin of outer overlapping

Taxonomy and biogeography of the family Isolapotamidae 1305

zone mesially projecting and sticking out, exible zone of rst gonopod present and elongated; distal part of subterminal joint neck-like, narrow; terminal part of second gonopod dorsoventrally attened; terminal tube extremely narrow, contact zone situated on mesial edge.

Remarks. Demanietta belongs clearly to the Isolapotamida e based on the morphology of the second gonopod. The cross-section of the terminal tube of the second gonopod agrees fully with that of Isolapotamon because it shows the narrow tube lumen and the characteristic contact zone of the lateral edges, as well as the fusion of the tube margin with the outer cuticle. Demanietta can easily be characterized by the morphology of the rst gonopod, especially of the terminal joint and the structure of the exible zone and the neck-like distal elongation of the subterminal joint. Demanietta was originally established by Bott (1966) as a subgenus of Potamiscus Alcock, 1909 . Bott (1970b) later transferred Potamiscus (Demanietta) to the genus Ranguna Bott, 1966 . Ranguna was regarded by other authors (Türkay and Naiyanetr, 1986; Holthuis, 1990; Ng, 1990) as a junior synonym of Potamiscus and the status of Demanietta became unclear. Naiyanetr (1992a) recognized Demanietta at the genus level, and Ng and Naiyanetr (1993) rede ned the genus on the basis of carapace characters, assigning its species to two genera, Demanietta sensu Ng and Naiyanetr, 1993 , with the type species D. manii , and Thaiphusa Ng and Naiyanetr, 1993 with the type species T. sirikit . According to Yeo et al. (1999) Demanietta and Thaiphusa can be distinguished by the following characters:

the rst gonopod terminal segment fold of Demanietta is relatively higher than in Thaiphusa ;

the carapace is relatively at with well-de ned regions, versus an in ated, rounded carapace with poorly de ned regions;

serrated and cristate anterolateral margins, versus low and rounded anterolateral margins;

rugose and sharp epigastric cristae and postorbital cristae clearly separated from each other, versus rounded epigastric cristae and postorbital cristae almost con uent with each other;

a broad to acutely triangular epibranchial tooth versus a low and rounded tooth;

rugose and striated branchial and metabranchial regions versus regions smooth;

a third maxilliped exopod agellum length subequal to, or greater than merus width, versus half to two-thirds as long as merus width.

Further, Demanietta tend to be aquatic, while species of Thaiphusa tend to be more terrestrial.

In my opinion the latter fact is the most important one. The described diOEerences in carapace and maxillipeds represent distinct ecological adaptations and are not necessarily indicators for taxonomical relations. Additionally, this kind of carapace structure occurs independently in diOEerent taxa, for example in the genus Thaipotamon , or in species of the family Gecarcinucidae . Thus, this carapace structure cannot be used as an exclusive taxonomic character for a special group.

The excellent gures of Yeo et al. (1999) show that some species of Demanietta have high similarities with T. sirikit . The best example is D. kharikhan Yeo et al., 1999 , which has a convex and smooth dorsal carapace, non-serrated lateral margins and low epibranchial teeth. This means that within the genus Demanietta several

Taxonomy and biogeography of the family Isolapotamidae 1307 species show all transitions in the carapace structures between strongly sculptured species such as D. manii and non-sculptured species such as D. sirikit . Additionally, Brandis (2000) argued for Potamiscus Alcock, 1909 , that the length of the third maxilliped agellum seems to be correlated with habitat. The more terrestrial the crabs are, the shorter the agellum. In this sense, these characters indicate diOEerent feeding modes and thus have to be considered as ecological adaptations, and can appear independently in non-related taxa and therefore are not meaningful for taxonomic classi cations of higher ranks.

Finally, D. manii and Thaiphusa sirikit share the same general rst gonopod morphology representing a special interaction mode between male rst gonopod and female gonopore. According to the results for the genus Potamon (Brandis et al., 1999) the copulation mode in Demanietta is characterized by a projection of the terminal joint of the rst gonopod, formed by the outer overlapping margin and the neck-like elongated exible zone. The only variations of gonopod 1 between D. manii and T. sirikit are the height of the projection and the shape of the exible zone, but this can be easily explained as a speci c character. In other groups of freshwater crabs examined the shape of the terminal joint of gonopod 1 represents a generic character exclusively typical for a special group of freshwater crabs. Therefore, Thaiphusa is here regarded as a junior synonym of Demanietta .