Which developmental process involves egg, young, and adult stages?

The developmental process that involves egg, young, and adult stages can be accurately characterized by no metamorphosis, also known as ametabolism. In this process, organisms develop through a series of life stages without undergoing significant morphological changes. The young, often resembling smaller versions of the adult, grow and mature into adults without distinct larval or pupal stages.

In contrast, complete metamorphosis involves four distinct life stages: egg, larva, pupa, and adult. Incomplete metamorphosis includes a nymph stage that somewhat resembles the adult but lacks fully developed wings and reproductive structures at earlier stages. Gradual metamorphosis, typically associated with incomplete metamorphosis, also implies multiple developmental changes that are significant enough to differentiate the life stages. Thus, the description given aligns specifically with the ametabolic process where the organism develops directly from egg to adult form without transitional larval stages.