Mesozoan.
/ˌmɛsə(ʊ)ˈzəʊə/, U.S. /ˌmɛzoʊˈzoʊə/; see also meso- comb. form. Zoology.
With plural agreement: a group of minute worms with no body cavity or organs other than reproductive cells, which are internal parasites of marine invertebrates and absorb dissolved nutrients directly from the host's tissues; (also mesozoa) worms of this group collectively.The Mesozoa were so named as being supposedly intermediate in structure between protozoans and metazoans. The group has traditionally been treated as a phylum, and latterly as two related phyla, Orthonectida and Rhombozoa.
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the world > animals > invertebrates > Mesozoa > [noun]
Mesozoa1877
1877 Q. Jrnl. Microsc. Sci. 17 144 The ‘Mesozoa’..may be characterized as multicellular organisms, composed of two kinds of cells, one layer of which..is a true ectoderm; whilst the second layer..constitutes the endoderm.
1877 T. H. Huxley Man. Anat. Invertebrated Animals 676 The representatives of a distinct division, the Mesozoa, intermediate between the Protozoa and the Metazoa.
1940 L. H. Hyman Invertebr. I. iv. 233 The Mesozoa in general have a solid two-layered construction, but their two layers do not correspond to the ectoderm and entoderm of Metazoa.
1964 T. C. Cheng Biol. Animal Parasites vii. 179/1 Most authorities on the Mesozoa now agree that infusorigens are hermaphrodites.
1972 Sci. Amer. Dec. 98/2 Observations on laboratory populations of Mesozoa make this distinction untenable.
1995 Sci. News 14 Jan. 19/1 There is no clear dividing line between protists, mesozoa, or metozoa other than an arbitrary one.
This entry has been updated (OED Third Edition, September 2001; most recently modified version published online March 2022).
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