Nannostelium ampullaceum gen. et sp. nov., a tiny new member of the protosteloid amoeba of the Cavosteliida (Variosea, Amoebozoa)

Protosteloid amoebae are slime molds characterized by simple sporocarp comprised only of a stalk and typically single spore. Recent molecular phylogenetic studies showed that protosteloid amoebae are scattered among the Amoebozoa, but most of them belongs to the Variosea. The Cavosteliida is one of the largest protosteloid group of the Variosea. We have established novel protosteloid amoeba strain YIP-63 from the fruiting body of jelly fugus Auricularia sp. The strain YIP-63 is unique to have a tiny sporocarp and amoeba comparing to the other protosteloid species, and trophic amoebae forming both round and branched shape. The molecular phylogenetic analyses based on 18S rRNA gene suggest that YIP-63 represents a novel lineage in the Cavosteliida. Therefore, we propose the new genus and new species for the strain YIP-63 as Nannostelium ampullaceum gen. et sp. nov. We provide morphological and molecular data on this novel protosteloid amoeba.