A Morphologically Simple Species of Acrasis (Heterolobosea, Excavata), Acrasis helenhemmesae n. sp.

In the course of a large-scale global survey of mycetozoans, amoeboid organisms that form fruiting bodies, a new species of Acrasis was discovered from several subtropical locales in Hawaii, Australia, Bermuda, and South Africa. We isolated four strains from dead, still attached, plant material, and one strain from attached bark of a tree. Each isolate forms simple uniseriate multicellular fruiting bodies typically consisting of two bottle-shaped, basal stalk cells and a chain of < 20 spores. The isolate from Bermuda often forms dichotomous simple branches, each consisting of < 10 spores. Amoebae from these new isolates are limax with eruptive pseudopodial formation and display rapid locomotion-characters indicative of amoebae in the excavate taxon Heterolobosea. These isolates form simpler fruiting bodies than is typical of the well-known Acrasis rosea. Although in the original description, A. rosea is known to form uniseriate fruiting bodies similar to our isolates, A. rosea isolates typically form more complex fruiting structures along side simple ones, but never strictly simple ones. Nuclear-encoded 18S rRNA gene phylogenies demonstrate that our five isolates form a highly supported clade that is sister to A. rosea. Given the differences both in gene sequences and fruiting body morphology between our isolates and A. rosea, we propose the new species, Acrasis helenhemmesae n. sp.