Microscopic evidence for inclusion of Parvamoeba Rogerson, 1993 into the order Himatismenida (Amoebozoa)

I have re-investigated the light-microscopic features of Parvamoeba rugata Rogerson, 1993, type strain CCAP 1556/1. The major characters of amoebae correspond to the initial description of this species. However, one peculiarity demonstrated by the cells during adhesion to the substratum, seems to have been partly underestimated previously. At the same time it is crucial for the explanation of this species' position in the molecular phylogenetic trees and the recent system of Amoebozoa. This feature is the formation of a thin sheet of hyaloplasm on the ventral side of the cell that is used for adhesion to the substratum and locomotion, shared between Parvamoeba and members of the order Himatismenida. This explains the position of Parvamoeba as a sister clade to Cochliopodiidae in the molecular phylogenetic trees and justifies the recent inclusion of this genus into the order Himatismenida. In addition I sequenced the small-subunit ribosomal RNA of P. rugata and demonstrated that it was 99.5-99.7% similar to that of P. monoura Cole et al., 2010. This raises a question of the possible identity of these two species, however, several persistent morphological differences do not permit the unification of them, at least until more genes demonstrate identical sequences between these species.