annulation

zoology

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June 18, 2026

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The term "annulation" in zoology refers to a ringlike anatomical structure. This can also describe an annulated state or structure, known as annulism.12

In some older classifications, "Annulata" was a major division of invertebrates characterized by bilateral symmetry and true metamerism, including annelids and arthropods. Similarly, "Annulosa" was a subkingdom comprising animals with articulate bodies, such as annelid worms and arthropods.34

Segmentation, or metamerism, is the condition of being constructed from a series of repeating body segments called metameres. This is evident in phyla like Annelida and Arthropoda. While some organisms may have external ringlike formations that resemble segmentation, these are superficial and not true segmentation.5

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segmentation
…groups, external ringlike formations, called annulations, occur in the covering tissues, sometimes so marked as to suggest segmentations; these formations prove to be only superficial, however, and are not indicative of true segmentation.
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…groups, external ringlike formations, called annulations, occur in the covering tissues, sometimes so marked as to suggest segmentations; these formations prove to be only superficial, however, and are not indicative of true segmentation.
Read More