抄録
Chaetonotids (Gastrotricha) are small 60-400μm in length, inhabit both the freshwater and marine environments. Their bodies are tenpin- or bottle- like shaped; flattened ventrally and arched dorsally. The sensory organs, brain, and pharynx are located in the anterior head. Posteriorly, a "furca" bears the adhesive organ. The locomotory cilia are restricted to the ventral surface, forming a pair of ciliary bands. The body wall is usually composed of the external cuticle of a flexible proteinous layer. In some gastrotrichs, the basal layer is locally thickened and specialized to form scales, spines, and hooks. The cuticular scales vary in arrangement and shape, depending on the species. The most common species are freshwater chaetonotid species that inhabit ponds, swamp, streams, and lakes. In these species male is entirely absent, thus the most chaetotonids reproduce by parthenogenesis. About 700 species of chaetonotids have been reported so far around the world. In Japan, 34 species were recorded from lakes, ponds, and swamps. Recently, 44 species have been found in the rice paddies. In this paper the natural history and diversity of chaetonotids are reviewed.
