Rhizamoeba polyura n. g., n. sp., and Uroidal Structures as a Taxonomic Criterion for Amoebae

Rhizamoeba polyura n. g., n. sp., is a marine amoeba isolated on the northeastern coast of the United States and cultivated in clonal culture on agar media. Its limax locomotive form (mean length 76 µ) advances by steady cytoplasmic flow and often trails a uroid of ragged filaments. Stationary forms often have extensive uroidal holdfasts. The majority of individuals are uninucleate, but many are bi- or multinucleate. The nucleus, which may be elongated into spindle- or comet-like shapes, contains a central nucleolus to which the presumptive chromosomal material is closely and asymmetrically apposed. Mitosis is of the pattern common in amoebae, with disintegration of the nucleolus. In amoebae generally, two principal categories of filamentous uroids can be distinguished on the basis of their form and their apparent method of formation: the villous knob and the adhesion uroid. The villous knob, which may also adhere to the substratum at times, is found in quite diverse amoebae. The genus Rhizamoeba, defined on the criteria of locomotive form, method of locomotion, kind of uroid, and mitotic pattern, is separated from the genus Trichamoeba and other amoebae with a villous knob. It is classified in the family Hartmannellidae. Observations of amoeboid movement in R. polyura are not completely compatible with the application of motive force at either the posterior or the anterior end alone.