Primitive groove in chick embryos is equivalent to amphibian:
Primitive groove is a midline depression along primitive streak where epiblast undergoes epithelial-mesenchymal transition regulated by SNAI2, downregulates E-cadherin, ingresses to replace hypoblast and become mesoderm and definitive endoderm. Functionally it serves as portal for internalization, comparable to amphibian blastopore through which bottle cells apically constrict and involuting marginal zone mesoderm enters to form archenteron. Both represent blastoporal openings for gastrulation; chick groove is linear due to massive yolk constraint while frog blastopore is circular, but molecul
Ref: Wolpert, Principles of Development, 5th ed., Chapter 5: Primitive groove homologous to amphibian blastopore.