Tubulina represents the largest
and best resolved lineage of Lobosea at the moment. This clade
comprises the families Amoebidae and Hartmannellidae, together
with the leptomyxids and the genus Echinamoeba (Amaral
Zettler et al. 2000; Bolivar et al. 2001; Fahrni et al. 2003).
The families Amoebidae and Hartmannellidae include all amoebae
that are normally subcylindrical in cross-section and are
polypodial or monopodial in locomotion. The lineage
corresponding to the order Leptomyxida groups all amoebae
possessing adhesive uroidal structures and capable to alter
their locomotive form from a flattened, expanded to a
subcylindrical, monopodial one.
The synapomorphic character of
the Tubulina is the ability to adopt a monopodial locomotive
form, subcylindrical in cross-section and to show
monoaxial flow of the cytoplasm. In the case of the
polypodial amoebae (Amoebidae), this process takes place in each
pseudopodium; however, nearly all normally polypodial amoebae
are also capable to adopt a monopodial (monotactic or
orthotactic) locomotive form (Grebecki and Grebecka
1978). The Leptomyxida and, to some extent, Echinamoeba
can also alter their locomotive morphology (Smirnov et al.
2004). Normally most of them are flattened, expanded organisms,
however, under the light beam or certain other conditions, all
leptomyxids can temporarily become monopodial (Page and
Willumsen 1983; Smirnov 1999a).