Hydrobiologia 446/447: 233–246, 2001. L. Sanoamuang, H. Segers, R.J. Shiel & R.D. Gulati (eds), Rotifera IX. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 233 Zoogeography of the Southeast Asian Rotifera Hendrik Segers Laboratory of Animal Ecology, Zoogeography and Nature Conservation, Dept. of Biology, Ghent University, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium E-mail: Hendrik.Segers@rug.ac.be Key words: Rotifera, zoogeography, diversity, Southeast Asia Abstract The distribution and taxonomic composition of Rotifera in Southeast Asia is reviewed. For some countries, records are poor: Brunei, Cambodia and Laos are almost terra incognita for rotifers (<10 taxa recorded), while the Thai rotifer fauna is the best documented (ca. 310 taxa on record). However, analysis of the available data is impeded by fuzzy taxonomy and the questionable reliability of many records. Most studies focus on the pelagic or littoral of freshwater habitats. Other habitats are largely ignored. Similarly, few studies deal comprehensively with illoricate Monogononta, sessile Flosculariacea and Collothecacea and, especially, Bdelloidea. The genera Lecane, Bra- chionus and Trichocerca are the best represented, with littoral taxa predominant. Fisheries-related studies dealing with highly productive pelagic environments tend to over report the contribution of Brachionus. Most taxa are thermophilic character, exemplified by the dominance of tropic-centred Lecane and Brachionus. Some cold-water taxa have been recorded, but the relative climatological homogeneity of the region and low number of studies on high-altitude environments prevent the discrimination of clear latitudinal or altitudinal variation in the distribu- tion of rotifers within Southeast Asia. The majority of Southeast Asian rotifers are widely distributed, including true cosmopolites and thermophilic taxa. There are several local or Oriental endemic Rotifera, mostly Lecane. The American Brachionus havanaensis and Keratella americana appear to have been introduced to the region. The taxonomy of some Rotifera described from the region is commented upon; Brachionus murphyi Sudzuki is recognised as senior synonym of B. niwati Sanoamuang et al. (syn. nov.). Some cases of geographical and/or ecological vicariant species-pairs are suggested. The Southeast Asian rotifer fauna contains a sizeable fraction of taxa occurring in the tropical regions of the Old World, most of which also occur in tropical Australia or the Austro-Malayan region. A tropical Australasian faunal component is present, but consists of few taxa only. Hence, affinities between the rotifer fauna of the Ethiopian, Oriental and tropical Australian and Austro-Malayan regions are supported, rather than an affinity between the Indo-Asian or Indo-Malaysian and tropical Australian fauna. Introduction To date, little is known of the zoogeography of South- east Asian Rotifera. There are quite a few publications reporting rotifers, but the accumulated data still con- stitute only a fragmentary record. The first reports included sketchy reports on collections from the Phil- ippines (Semper, 1875: description of Trochosphaera aequatorialis), and Java (Indonesia: Weber, 1907; Van Oye, 1922a–c, 1924; Slonimski, 1925). An interesting early contribution is by Heinis (1928), who repor- ted on the recovery of the moss-dwelling microfauna from Krakatau after the massive volcanic explosion of 1883. The publication of Hauer’s (1937, 1938) “Die Rotatorien von Sumatra, Java und Bali” constituted a milestone in the development of the scientific record of Southeast Asian Rotifera. The biogeography of Southeast Asia is of special interest because of the particularly complex geological and biological history of the region. Mainland South- east Asia joined with Eurasia in the Triassic, but the movements and collisions of its lithospheric plates, and the northwardly movement of the Australian con- tinent, result in ongoing processes of mountain form- ation. The southern islands of Southeast Asia have a diverse geological origin, which can be illustrated by