An anthostome is an animal of the phylum Anthostoma (lit. "flower mouths"), and is one of two phyla (body plans) of animals on TIRA 292b. Beginning as sessile aquatic animals, clades of Anthostoma have evolved to become mobile, eventually becoming the first terrestrial clade of animals, as well as the first clade of flying animals.
The first of the Anthostoma was Archeanthostoma. In addition to being one of two animal phyla on the planet, however, Anthostoma forms a clade with Archeanthostoma and Gastrozoa.
Anthostomes first emerged around 4008ma, beginning as sessile, radially symmetrical organisms. While these forms of Anthostoma exist into the present day, the Tentaclostoma branch developed motility and bilateral symmetry. This later led to the Lophostoma branch, the earliest clade of terrestrial animals on the planet.
Describing Anthostoma in broad strokes is difficult, as the evolutionary process has resulted in clades with highly divergent anatomies. The
- A single orifice, from which food is ingested, waste is excreted, and sex cells are excreted
- Largely soft-bodied, with little, if any internal support structure: in species with support structures, it is almost always a shell