Stygamoeba regulata n. s p. (Rhizopoda) — A Marine Amoeba with an Unusual Combination of Light-Microscopical and Ultrastructural Features

Abstract

Summary Light-microscopical examination of Stygamoeba regulata n. sp. showed that this marine amoeba moved steadily, frequently producing an advancing anterior lobopodium as a result of gentle streaming of the cytoplasm. Moreover, S. regulata had no flagellate stage in the cell cycle. At the ultrastructural level, the cells had distinctive dictyosomes. These characters are consistent with inclusion in the class Lobosea. However, electron microscopical examination also showed that S. regulata had flattened mitochondrial cristae, which is a feature common to the class Heterolobosea. Because of these inconsistencies, it is proposed to remove the genus Stygamoeba Sawyer , 1875 from the class Lobosea, order Leptomyxida, family Stereomyxidae and to consider it as a genus insertae sedis within the phylum Rhizopoda. Ultrastructural information on the type species, Stygamoeba polymorpha Sawyer , 1975 is required before definitive conclusions can be drawn concerning the homogeneity and systematic position of this genus.