The structure that caused rotifers to be called wheel animals or wheel bearers is the corona.
Rotifers are also known as wheel animals or wheel bearers because of the corona structure around their mouth region.
Some rotifers are sessile and live inside tubes or gelatinous holdfasts that are attached to a substrate. Other rotifers migrate around a substrate through inch worming.
This is because when corona is seen in a sequential coordinated movement, it resembles the structure of a wheel, although it does not rotate in reality.
Therefore, we conclude that rotifers are called wheel animals or wheel bearers due to the presence of the corona structure.
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