English name: Sea urchin Scientific name: Psammechinus sp. Familia: Echinidae Classis: Echinoidea Phylum: Echinodermata Regnum: Animalia
After the morula stage the blastomeres arrange so a mono-cellular coat around a central vacity (the blastocoel) is formed. This stage is called the blastula stage (blastula = vesicle-like). The embryo secretes a hatching enzyme that causes proteolytic degradation of the fertilization membrane. The epithelium of the cells at the vegetal pole thickens. The vegetal plate arises. To next stage. One stage back.
