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Rhizamoeba has been placed with Leptomyxa and Gephyramoeba in the Family Leptomyxaidae however reservations have been raised  (Page, 1983).  Recent SSUrDNA data (Amaral Zettler et al, 2000) suggest a kinship between Rhizamoeba and Paraflabellula, in fact the single Rhizamoeba analysed split Paraflabellula hoguae and P. reniformis.  This study also indicated a relationship to Leptomyxa reticulata, but not to Gephyramoeba.  A more recent study supports these relationships (Peglar et al, 2003).  Rhizamoeba together with Paraflabellula, Leptomyxa, Saccamoeba, Hartmannella and Echinamoeba have been grouped together in the LH lineage (Peglar et al, 2003) by SSUrDNA gene sequence analysis although these genera are very different in appearance!

Rhizamoeba in rapid locomotion is limax with a hyaline crescent, the rear is often a mass of adherent colosomes.  Can transform into a flabellate form no cytoplasmic crystals.  Similarity has been observed at the ultrastructural level between Rhizamoeba and Leptomyxa (Cann, 1984). Both mononuclear and polynuclear species described.  Species described from both salt and freshwater

Described species:-

R. australiensis
R. caerulea (Schaeffer 1926), 150-250mm. Named for its blue colour.
R. clavarioides  125-150mm. uninucleate
R. flabellata Multinucleate with a very large range of size 50-500mm. Double walled cysts 40mm in diameter but like the amoebae , very variable (Page, 1988). Mitochondria round or cylindrical with tubular cristae.  Golgi arranged as stacks (Cann, 1984).
R. saxonica
Available strains (SSUrDNA data in black):-

Rhizamoeba sp. strain EPA 20(ATCC 50743). 

Rhizamoeba saxonica ATCC50812 Sawyer, T.K., 
Rhizamoeba saxonica ATCC50742 AY121847

Amaral Zettler, L.A., Nerad, T.A., O'Kelly, C.J., Peglar, M.T., Gillevet, P.M., Silberman, J.D. & Sogin, M.L. (2000). "A molecular reassessment of the Leptomyxid amoebae." Protist 151, 275-282.

Cann, J.P. (1984). "The ultrastructure of Rhizamoeba flabellata (Goodey) comb. nov., and Leptomyxa reticulata Goodey (Acarpomyxea: Leptomyxida)." Arch.Protistenk. 128: 13-23.

Page, F.C. (1983). "Marine Gymnamoebae." Inst.Terr.Ecol. NERC Cambridge, England.

Peglar, M. T., Amaral Zettler, L. A., Anderson, O. R., Nerad, T. A., Gillevet, P. M., Mullen, T. E., Frasca Jr, S., Silverman, J. D., O'Kelly, C. J. & Sogin, M. L. (2003) Two new small-subunit ribosomal RNA gene lineages within the subclass Gymnamoebia., J.Eukaryot.Microbiol. 50, 224-232.


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