In: Biology
Compare human and sea urchin development prior to and after the gastrula stage.
Human gametes and sea urchin gametes are of same size and both of their development is quite similar through the gastrula stage. Both of them are deuterostomes with radial cleavage. At a distant site of gastrulation originates mouth.
The gastrulation of sea urchin begins from the flattened epithelium at vegetal pole of the embryos called vegetal plate. It invaginates following PMC to form stout cylinder called archenteron. Secondary mesenchymal cells present at tip of archenteron begins to elongate across blastocoel and touches the ectoderm. Then PMCs secrete spicules. The ectoderm then flattens forming prism stage. Then gut, endoderm, skeleton differentiate to make pluteus larva.
Formation of primitive streak is the first stage of gastrulation in human. The strike is the more like of body which separates into right and left side. This imparts bilateral symmetry. The three corresponding layers invaginate starting from endoderm, mesoderm and ectoderm. Below primitive streak mesoderm forms notochord from a thin rod of cells.