Biology of Finfish and Shellfish (2+1)

4.11.5. 3^rd Stage

The whole embryo has become more arched dorsally, and more marked off from the yolk. On the latter, the blastoderm, which consists of two layers, an external ectoderm and an internal yolk membrane, has spread out further towards the ventral (vegetative) pole of the egg. At the posterior edge of the rudiment of the visceral dome, the mantle fold has grown out forward in such a way as to form a small mantle cavity, which already partly covers the rudiments of the gills: In the space between the rudiments of the funnel and the gills, the proctodaeum has formed by invagination, and its aperture, the anus could be seen. The rudiment of the fifth pair of arms appears.