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. [1]

中生動物（學名：Mesozoa）是一類細小的海洋無脊椎寄生動物，目前仍不清楚牠们是由扁形動物退化而成，还是獨立發展而來。 過去中生動物曾被劃為一個 門 或 亞界 ，但 分子遺傳學 研究顯示中生動物實為 多系群 ，由互不相關的動物類群所組成。

中生动物门 (Mesozoa)所有种类的通称，为一类介于原生动物与 后生动物 之间的微小多细胞动物，似为两者之间「遗失的一环」。形小，长不足1毫米至数毫米。

mesozoan, any of approximately 50 species of small, ciliated, multicellular animals that parasitize other marine invertebrates belonging to the phyla Rhombozoa and Orthonectida. These wormlike organisms lack digestive, respiratory, nervous, and excretory systems; their bodies consist of two layers of as few as 20 to 30 cells each.

由轴细胞可以产生线虫形幼体，也称蠕虫形幼体（vermiform larvae），幼体形成后离开母体，进入感染期，特别是在年幼或未成熟的寄主体内，通过这种无性生殖方式以增加群体的数量与密度。 当寄主成熟之后，或寄主体内种群数量极大时，轴细胞变成了两性腺，它同时可以产生精子与卵子，并在体内受精，受精卵发育成滴毛形幼虫（infusoriform larvae），幼虫也具纤毛指向后端，前端有两个细胞不具纤毛。 幼虫随寄主排泄物排到海水中，以后的生活史不详，可能又重新进入 …

中生动物门(Mesozoa)是一类小型的内寄生动物，目前已报道过的只有100种左右。 它们结构很简单，身体呈蠕虫形，体长不超过9mm，具有复杂的生活史。 中生动物

2014年1月1日 · Members of this phylum represent the simplest of all multicellular animals, and are characterized by tiny, wormlike, parasitic organisms having a single layer of ciliated, epithelial cells that enclose one or more reproductive cells (Stunkard, 1954; McConnaughey, 1963).

Phylum Mesozoa The name Mesozoa (mes-o-zo´a) (Gr. mesos, in the middle, + zoon, animal) was coined by an early investigator (van Beneden, 1876) who believed that the group was a “missing link” between protozoa and metazoa. These minute, ciliated, wormlike animals represent an extremely simple level of organization.

2024年5月21日 · Mesozoa are tiny, simple, worm or blob-like parasites that were once thought of as intermediates between protozoa (motile single-celled organisms) and metazoa (multicellular animals). However, now they are generally thought of as degenerate metazoa, that is, metazoans that descended from more complex animals but were secondarily simplified.

Mesozoans are all tiny organisms that have a very simple structure: the body wall consists of a thin outer membrane that is dotted with large numbers of small cilia. When they beat, they provide a means of locomotion through the host animal's body fluids. The vast bulk of the mesozoan body consists of egg and sperm cells.