The Mesozoa are minuscule, worm-like parasites of marine invertebrates. Generally, these tiny, elusive creatures consist of a somatoderm (outer layer) of ciliated cells surrounding one or more reproductive cells.
A 2017 study recovered Mesozoa as a monophyletic group that emerged in the Lophotrochozoa as sister of the Rouphozoa.
Agnotozoa is a subkingdom of simple animals that is sometimes used. It is one of the three "traditional" animal subkingdoms, along with Parazoa and Eumetazoa. On some classifications, it is nearly synonymous with Mesozoa.
Agnotozoa was first used as one of the branches of the subkingdom Metazoa. It was then considered to contain only one group, Mesozoa.
View the full Wikipedia page for Agnotozoa