ملف:Left-right asymmetry in the sea urchin - journal.pbio.1001404.g001.png

English: Left-right asymmetry in the sea urchin.

During cleavage, mesoderm (red cells at 60-cell stage) and small micromeres (purple cells at vegetal pole) become specified. At the end of gastrulation, progeny of these two cell types contribute to the coelomic pouches (red and purple outpockets seen at the tip of the archenteron). During larval stages, the adult rudiment grows from the left coelomic pouch. After metamorphosis, that rudiment grows to become the adult. Embryonic axes are shown relative to the 60-cell cleavage and gastrula stages. The aboral-oral axis is also known as the dorsal-ventral axis. The animal-vegetal axis is the only axis established prior to fertilization. Oral-aboral axis specification occurs early in cleavage, and left-right axis determination occurs at the late gastrula stage.

doi:10.1371/journal.pbio.1001404.g001