Placozoa

Placozoa taxonomy

This is a very small group (only one or two species have been described) that have been linked to the Mesozoa and the Cnidaria in the past. Their phylogenetic position is not clear, but they seem to closer to the Porifera than to other Phyla.

Placozoa body pattern and physiology

They are all very small; usually only two or three millimetres across. They glide over the substratum on flagellated cells. Their dorsal surface also has gland cells which secrete enzymes to digest their prey.

Their body has just 2 layers; a thin dorsal epithelium of flagellated cells, and a thicker ventral epithelium also of flagellated cells, but also with glandular cells.