1. Plural of gastraea; a hypothetical ancestral form of multicellular animals consisting of a simple two-layered sac with an outer and inner cell layer.
Usage: biology; historical; developmental biology

Examples

• The gastraea theory proposed that all multicellular animals descended from a common gastraea-like ancestor.
• Early embryologists studied gastraeas to understand the origins of body layers in animals.
• The concept of gastraeas was influential in 19th-century evolutionary developmental biology.