Meanings
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1
noun
the terminal dorsal plate or last exposed abdominal segment of certain insects
The beetle's pointed pygidium extended beyond the ends of its wing cases.
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2
noun
the fused posterior shield of a trilobite or the comparable tail region of some other arthropods
The fossil's pygidium remained attached even though most thoracic segments were missing.
Thesaurus
Etymology
Coined in New Latin from Greek pyge ("rump, buttocks") + the diminutive suffix -idium. Zoologists use it for the terminal body plate or fused tail shield of several arthropod groups.