Mesozoa is a small and enigmatic phylum of animals that includes a relatively small number of species. As of my last knowledge update in September 2021, Mesozoa is divided into two classes:
- Rhombozoa (Class Rhombozoa):
- Rhombozoans are microscopic parasitic organisms that are primarily found in the kidneys and reproductive organs of marine invertebrates, such as mollusks and flatworms.
- They have a simple body plan with a few cells and are often considered one of the simplest multicellular organisms.
- The class Rhombozoa includes the genera Dicyema and Dicyemennea.
- Orthonectida (Class Orthonectida):
- Orthonectids are also microscopic parasites that inhabit the body cavities and tissues of marine invertebrates.
- They have a more complex body plan compared to rhombozoans, consisting of layers of cells.
- Orthonectids can be found in various marine hosts, including annelid worms and echinoderms.