Cladocera (Crustacea: Branchiopoda) of South East Asia: history of exploration, taxon richness and notes on zoogeography

The history of Cladocera studies in South-East Asia is reviewed, beginning from the early start of explorations in the end of the 19th century by J. Richard and T. Stingelin. In the first half of the 20th century, extensive research was carried out by V. Brehm, who investigated material collected by the Wallacea-Expedition and the Deutschen Limnologischen Sunda-Expedition. Later, in the 1970-1980s, C. H. Fernando and collaborators, besides a few other researchers, provided a new series of regional studies of the cladoceran faunas together with the systematic revisions of some taxa from tropical Asia. Then and up to present, investigations of the Cladocera have concentrated in Thailand and many species have been revised and described as new to science. In total, 298 taxa of species rank have been recorded in SE Asia but only comparatively few of them (67 taxa; 22.5%) can be regarded good species, of which the valid status has been confirmed by recent studies, while others are synonyms (68; 22.8%) or taxa of uncertain taxonomic status, including those which definitely represent complexes of species (163; 54.7%). Most total taxa of species level and good species are known from Thailand (155 and 54, respectively), followed by Malaysia (plus Singapore), Indonesia, Philippines, Vietnam, and Cambodia in this respect (70119 total taxa and 23-33 good species respectively). Laos, Burma (Myanmar) and Brunei remain practically unexplored. Only good species were used for the zoogeographic analysis. Of them, about a quarter is known only in SE Asia but more species are distributed in tropical/subtropical/temperate Asia and Australia, others in tropics/subtropics of the eastern hemisphere (17.9%) or even wider. Tropical species, constituting the primary part of the cladoceran fauna of SE Asia, can penetrate the neighboring subtropical and southern temperate zones to a different degree. Only a small fraction of species (7 or 10.5%) here are of more or less northern origin, they are distributed predominantly in the subtropical/southern temperate or in the northern boreal latitudes. Few species are suggested to penetrate SE Asia from the north using the Mekong river and its tributaries. Generally, the cladocerans of SE Asia are poorly known and only continuous extensive taxonomic studies would improve this situation.