Ultrastructural details of the plasmodial rhizopod Synamoeba arenaria Grell

During the last years, several plasmodial protists of the littoral zone hav e been discovered, cultivated, and characterized. Here, we present and disc uss results on the ultrastructure of Synamoeba arenaria Grell. Especially c haracteristic in S. arenaria ultrastructure is the microtubule-organizing c entre (MTOC). This plaque-like structure is positioned in proximity to the nucleus and comprises two electron-dense plaques separated by a transparent , partly granularly structured, cleft. During nuclear division MTOCs divide via typical V-shaped intermediary structures. The ultrastructure details o f the MTOC suggest a phylogenetic relationship between Synamoeba arenaria a nd Corallomyxa chattoni and Stereomyxa ramosa.