Expansion of the ‘Reticulosphere’: Diversity of Novel Branching and Network-forming Amoebae Helps to Define Variosea (Amoebozoa)

Amoebae able to form cytoplasmic networks or displaying a multiply branching morphology remain very poorly studied. We sequenced the small-subunit ribosomal RNA gene of 15 new amoeboid isolates, 14 of which are branching or network-forming amoebae (BNFA). Phylogenetic analyses showed that these isolates all group within the poorly-known and weakly-defined class Variosea (Amoebozoa). They are resolved into six lineages corresponding to distinct new morphotypes; we describe them as new genera Angulamoeba (type species Angulamoeba microcystivorans n. gen., n. sp.; and A. fungorum n. sp.), Arboramoeba (type species Arboramoeba reticulata n. gen., n. sp.), Darbyshirella (type species Darbyshirella terrestris n. gen., n. sp.), Dictyamoeba (type species Dictyamoeba vorax n. gen., n. sp.), Heliamoeba (type species Heliamoeba mirabilis n. gen., n. sp.), and Ischnamoeba (type species Ischnamoeba montana n. gen., n. sp.). We also isolated and sequenced four additional variosean strains, one belonging to Flamella, one related to Telaepolella tubasferens, and two members of the cavosteliid protosteloid lineage. We identified a further 104 putative variosean environmental clone sequences in GenBank, comprising up to 14 lineages that may prove to represent additional novel morphotypes. We show that BNFA are phylogenetically widespread in Variosea and morphologically very variable, both within and between lineages.