The phylogeography of Simulium siamense complex was inferred from mitochondrial DNA sequences. A 586-bp fragment of the cytochrome oxidase I was sequenced for 92 individuals from 13 populations throughout Thailand, representing five cytoforms (A, B, C, F and G). The cytoforms are not genetically different at the molecular level except for cytoform B, which is genetically distinct from the others. This might indicate that cytoform B is a distinct species. Further morphological and molecular work using other genes is needed to clarify this. Our results also argue for the need of integrated approach, both cytological and molecular studies to understanding biodiversity of black flies. The star-like shape of the mtDNA genealogy is consistent with the sudden population expansion of the mismatch distribution analysis and large negative values of Fu's Fs and Tajima's D-tests, indicating a population demographic expansion. The expansion time is estimated to be in the late Pleistocene (about 120 000 years ago). Therefore, the overall low level of genetic structure could be due to sharing a recent history. The ancestral haplotype was found in the mountainous area in northeastern Thailand, suggesting that this area could have been the refugium of the species complex during the Pleistocene glaciations. Our results are consistent with previous findings about population expansion in response to the Pleistocene climatic change, thus revealing the importance of this historical event in shaping the genetic structure and diversity of Southeast Asian mainland species.

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The status of species currently assigned to the Southeast Asian Elephant Pupinid snail genus Pollicaria Gould, 1856 is reassessed. Shell, radular and reproductive morphology are investigated and analysed with reference to karyotype patterns previously reported and to distribution patterns among the species. Six previously described species are recognised: Pollicaria gravida (Benson, 1856), Pollicaria myersii (Haines, 1855), Pollicaria mouhoti (Pfeiffer, 1862), Pollicaria elephas (Morgan, 1885), Pollicaria crossei (Dautzenberg & d’Hamonville, 1887) and Pollicaria rochebruni (Mabille, 1887). A new subspecies, Pollicaria mouhoti monochroma ssp. n.,is proposed and a dichotomous key to species is provided.

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Morphological and chromosomal characteristics of a number of unionid freshwater mussels were studied from northeastern Thailand. Karyotypes of eight species from seven genera (Chamberlainia, Ensidens, Hyriopsis, Physunio, Pseudodon, Scabies and Trapezoideus) were examined. Six species possess 2n = 38 karyotypes, whereas Scabies crispata and an unidentified Scabies sp. lack three small chromosome pairs, giving a diploid number of 32. Moreover, the karyotypes of the unidentified Scabies differ from Scabies crispata as it exhibits a telocentric chromosome pair (6m + 7sm + 2st + 1t). Most of the conchological characters also differ between the two species – adult size, colour pattern, muscle scars, pseudocardinal and lateral teeth. The name Scabies songkramensis sp. n. is proposed for the unidentified species, and its description is included in this paper. Interestingly, seven species contain mostly bi-armed chromosomes, but only the mud-dweller in stagnant water, Ensidens ingallsianus, contains predominantly five telocentric pairs. In addition, the marker chromosome characteristics of an unbalanced long arm, twisted centromere, a wider angle 180° arrangement, a twisted arm and telomeric end union reported in this study are described for the first time for unionid mussels.