puparium = the hardened last larval skin which encloses the pupa in some insects, especially higher diptera; a pupa enclosed in a puparium.

Shingo Tamagawa, an animator closely associated with the studio Sunrise, was afraid he’d start hating his drawings, and even the act of drawing, if he continued to pursue the path he was on. “No matter how hard your work,” he explains in the new documentary Three Minutes, Three Years: Making Puparia, “animation is something that is consumable.” Disillusioned, he stopped drawing for over a year. In that time, ideas slowly started accumulating for a new short film. After three years of solo production, his three-minute indie film Puparia was completed. He released it in November on YouTube, where it has since been viewed more than a million times

Source (How The Hit Short Film ‘Puparia’ Was Born From Frustration With The Anime Industry, CartoonBrew, 02.03.2021)