The body is two epithelial layers with a loose middle containing contractile fibre cells, and only around six to eight distinct cell types have been identified, fewer than in any other animal. There is no front or back, no left or right, and the outline changes continuously as the animal moves by ciliary gliding.
Feeding is external. The placozoan settles over a patch of algae or biofilm, lifts slightly to form a temporary pocket, secretes digestive enzymes from gland cells on its lower surface, and absorbs the products. When the food is gone it simply moves on. Reproduction is usually by fission or budding.
Despite the simplicity, the genome is not simple: it encodes many genes associated with nervous and developmental systems in more complex animals, including components of synaptic machinery, without the structures themselves. Where Placozoa sits in the animal tree, and whether its simplicity is ancestral or secondarily reduced, is genuinely unsettled.