It is a member of Pluriformea inside the lineage of Holozoa, a clade containing animals and their closest protistan relatives.

It has a complex life cycle that includes unicellular amoeboid and flagellated phases, as well as multicellular aggregates, depending on the growth medium and nutritional state.

There is one smooth flagellum that emerges from the middle-lateral point of the cell, turns back, and directs backwards during swimming.

Floating cells move downwards to transform into amoeboflagellates by generating wide lobopodia and thin short filopodia, and slowing the flagellar beating.

They can also aggregate by joining only flagellated cells together, with their flagella directed outwards, resembling the rosette-like colonies of choanoflagellates.

This phenomenon of budding from syncytia has not been observed in any other eukaryotes, although the formation of multinucleated cells as a result of aggregation of multiple cells is known in other protist lineages (dictyostelids in Eumycetozoa, Copromyxa in Tubulinea,[4] acrasids in Excavata,[5] Sorogena in Alveolata,[6] Sorodiplophrys in Stramenopiles, Guttulinopsis in Rhizaria,[7] and Fonticula alba within the opisthokonts).

The formation of Syncytia also occurs in animals; the cytoplasm of glass sponges, teguments of flatworms, and the skeletal muscles and placenta of mammals are all syncytial structures.

It feeds on the cytoplasmic content of other eukaryotes of similar size, which is an unusual trait among unicellular holozoans.

However, bacteria alone are not sufficient nutrition for Syssomonas: without any eukaryotic prey, their cells die or form resting cysts.