A second species that is sometimes mentioned, Treptoplax reptans, has never been found again after its first and only report and is not an accepted species rather than most likely a fragmentated Trichoplax. With only one species in the phylum the latter knows only three taxonomic ranks: Phylum (Placozoa), genus (Trichoplax), and species (T. adhaerens).

Genetic analyses have suggested that Placozoa harbor at least seven major species clades which may represent different orders with multiple families inside.

The estimated total number of placozoan species is at least 80 species, but the absence of documented morphological and ecological differences and the lack of life-cycle information still hinder the assignment of new species and higher taxonomic units.

The placozoan species database will be updated immediately whenever a relevant manuscript becomes accepted. Please send relevant information to Bernd Schierwater.