[1] It belongs to the subfamily Astomonematinae within the family Siphonolaimidae, along with another genus Parastomonema; both these genera have reduced digestive systems and paired ovaries.

[1] Astomonema and the related genus Parastomonema are distinguished from other members of the family Siphonolaimidae by their lack of a mouth, highly reduced pharynx, and modified midgut that contains prokaryotic symbionts.

[6] Their relatives are sulfur-oxidizing chemoautotrophs that use energy from oxidation of sulfur compounds in the environment (e.g. sulfide) to fuel the production of biomass by carbon fixation.

The symbionts of Astomonema are likely to also be sulfur-oxidizers because they have at least one of the key genes, aprA, encoding the alpha subunit of adenylyl-sulfate reductase, involved in the metabolic pathway of sulfur oxidation.

[6] This is an example of chemosynthetic symbiosis, where symbiotic prokaryotes use chemical energy to produce biomass and feed their host animals, which often have highly-reduced digestive systems.