What are Basal Metazoans?
The term “basal metazoans” refers to animals at the base of the metazoans’ (multicellular animal) evolutionary tree. The term isn’t very well-defined, and may refer to cnidarians (jellyfish and relatives), porifera (sponges), ctenophores (comb jellies), placozoans (the only animal phyla with a single species, Trichoplax adhaerens), and extinct species which may be more primitive than the common ancestor of all living metzoans (also called stem metazoa, mostly Ediacaran fauna). The most basal of all living metazoans may be Trichoplax adhaerens, a simple, very small (0.5 mm) balloon-like animal named for its propensity to stick to the sides of a glass aquarium. Trichoplax has the smallest genome out of any known animal, with only 50 megabases of DNA, and 6 chromosomes. The sequencing of the Trichoplax genome is currently underway. It is suspected that it may be related to cnidarians and ctenophores. Some recent molecular studies suggested that Trichoplax may have split from the rest of a
