BioEssays regularly runs a feature called "My Favorite Animal"; this month's choice is barely an animal at all, the placophoran Trichoplax adhaerens. I've written about Trichoplax before. It's a strange creature, a small flat blob that creeps amoeba-like over the substrate, that replicates by simply splitting in two, and that seems to have no distinguishing features at all—no head, no sense organs, no nervous system, no gut, just a collection of cells that hang together and slurp up algal slime. They are, however, multicellular, and their bodies contain at least four functionally distinct cell types, and the molecular evidence suggests affinities to other animal groups (they have a ProtoHox/ParaHox gene, for instance)…so they are definitely metazoans. They are just the simplest, barest kind of metazoan we can find now.
Continue reading Mysterious Trichoplax (on Pharyngula)