A 2017 study recovered Mesozoa as a monophyletic group that emerged in the Lophotrochozoa as sister of the Rouphozoa.

[1] Some workers previously classified Mesozoa as the sole phylum of the lonely subkingdom Agnotozoa.

[2] In the 19th century, the Mesozoa were a wastebasket taxon for multicellular organisms which lacked the invaginating gastrula which was thought to define the Metazoa.

[7] Rhombozoa, or dicyemid mesozoans, are found in the nephrid tracts of squid and octopuses.

The multinucleate syncytial stage lives within tissues and spaces of the gonad but can spread into arms.

It causes the destruction of starfish ovary and eggs to cause castration (the male gonads are usually unaffected).

The stages of the plasmodium develop into more plasmodia by simple fragmentation; at some point, they decide to go sexual.