On the Organization of the Naked Filose Amoeba,Nuclearia moebiusi Frenzel, 1897 (Sarcodina,Filosea) and Its Implications1

The ultrastructural organization of Nuclearia moebiusi is described. The organism has filose pseudopodia without supportive microtubules; it has mitochondria with flattened cristae, lacks extrusomes, microtubule-organizing centers, and cytoplasmic microtubules. During cell division, microtubules appear only within the nucleus, and reorganization of the nuclear envelope occurs late in the nuclear division cycle. Ultrastructural studies reveal that Nuclearia spp. have a pattern of cellular organization distinct from that of other amoebae. Comparison of ultrastructural features suggests that this organism is only distantly related to other rhizopod amoebae (including other filose amoebae) and to the heliozoa.