Definition of mesozoan
- a minute worm which is an internal parasite of marine invertebrates. It lacks any internal organs other than reproductive cells, and dissolved nutrients are absorbed directly from the host’s tissues.
- Phyla Orthonectida and Rhombozoa; formerly placed together in the phylum Mesozoa, which was thought to be intermediate between protozoans and metazoans
early 20th century: from modern Latin Mesozoa (from mesos 'intermediate' + zōion 'animal') + -an