MORPHOLOGICAL COMPARISON OF KERATELLA AMERICANA CARLIN, 1943 AND KERATELLA COMMON SPECIES IN TROPICAL CHINA

Keratella americana Carlin, 1943 mainly distributes in the America, and it had also been found in other continents. When we investigated zooplankton in South China in 2015, the species was found in Xingyun Lake, Fuxian Lake, Baise Reservoir and Feilaixia Reservoir. Its mitochondrial cytochrome oxidase subunitⅠ(COⅠ) gene was sequenced and showed a similarity of 98% with the sequences from GenBank, and this confirmed the species as K. ame-ricana. In the present study, a description was given of K. americana. Its trophi were compared with these of three common species:Keratella cochlearis (Gosse, 1851), Keratella tropica (Apstein, 1907) and Keratella tecta (Gosse, 1851), using a scanning electron microscope. K. americana is characterized by the following features:width of lorica narrower than its length; intermediate spines shorter than lateral spines; last facet in dorsal plate polygonal, open. The trophi of the four species differ in the shape of the fulcrum:The fulcrum of K. americana is stronger than the other three species. K. cochlearis has a T-shaped fulcrum and that of K. tropica is fan-shaped. The fulcrum of K. tecta is straight. The fulcrum therefore appears to significantly differ in shape and can be used for taxonomy and identification of diffe-rent Keratella.