(In a rotifer) a ring of cilia that is used in feeding and (in most kinds) swimming.
- The corona is retractile, with two trochal discs which are highly reduced, in Philodinavus to a small, bilobated, ciliated area; in Abrotrocha to a pair of lobes on either side of the prominent rostrum.
- In living animals, such as in Macrotrachela quadricornifera, the trochal discs with their beating cilia resemble rotating wheels, which is why these animals are called ‘rotifers’ or ‘wheel animalcules’.
- There are many variations to the corona pattern and in bdelloids it is composed of two ciliary rings: the anterior named trochus (divided into right and left each known as trochal disks) and the posterior called cingulum.
Mid 19th century: trochal from Greek trokhos 'wheel' + -al.
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Syllabification: tro·chal disk
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