egg sac
Quick Summary
An egg sac is a protective casing for eggs, found in various animals. In zoology, it can refer to an egg case, or specifically to the paired egg masses seen on certain crustaceans like copepods.1
For sharks and rays, egg sacs are horny shells that enclose large, yolk-rich eggs. These shells can have tendrils or spikes for anchoring and vary in shape. Some species are oviparous (egg-laying), while others are ovoviviparous, where the egg hatches inside the mother.2
Spiders also produce egg sacs, typically made of silk, which can contain anywhere from a few to a thousand eggs. Female spiders may guard these sacs or carry them, and some species die after laying their last egg sac.3
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