Blastoderm

Definition

A single-layered sheet of embryonic epithelial cells that forms the wall of the blastula, enclosing the fluid-filled blastocoel. In many arthropods, including most insects, the blastoderm develops through superficial cleavage: nuclei divide repeatedly within a common yolky cytoplasm before cellularization produces the definitive epithelial layer. Gastrulation subsequently folds the blastoderm to generate the three primary germ layers—ectoderm, mesoderm, and endoderm—establishing the body plan.

Etymology

From Greek blastos (sprout, germ) + derma (skin, layer)

Example

In Drosophila melanogaster, the syncytial blastoderm stage contains approximately 6,000 nuclei arranged in a monolayer beneath the egg surface; following cellularization, this becomes the cellular blastoderm that undergoes gastrulation to form the segmented body axis.

Synonyms

• cicatricula

Related Terms

• blastula
• blastocoel
• gastrulation
• germ layer
• syncytium
• cellularization
• superficial cleavage

Usage Notes

In insect embryology, specialists distinguish the syncytial blastoderm (nuclei sharing common cytoplasm) from the cellular blastoderm (individual cells with complete membranes). The term is sometimes used more broadly in vertebrate embryology, but the superficial cleavage pattern makes it particularly characteristic of arthropod and especially insect development. Not to be confused with blastodermic vesicle or blastodisc terminology used in amniote eggs.