The term "egg case" refers to a protective covering that contains eggs. However, there are many different words you can use as synonyms for this term, depending on the type of animal the eggs come from. For example, the egg case of a shark is called a "mermaid's purse," while a spider's egg case is referred to as an "ootheca." The egg sac of a moth is called a "cocoon," while a dragonfly's egg case is known as an "exuvia." Other synonyms for egg case include "capsule," "pod," "nursery," and "pouch." So, no matter what type of egg you are talking about, there are many different ways to describe its protective covering.