Biology of Finfish and Shellfish (2+1)

4.11.3. 1^st Stage

In the centre of the germinal disc there is an oval-rhombic bulging which is the rudiment of the visceral dome and the mantle. On each side, a bean-shaped prominence, the rudiment of the eye appears. Behind the eye, on each side, a long narrow ridge runs backward in a curve; about half way down. This ridge is a small prominence, the rudiment of the funnel cartilage, forms close to its outer side. The part of the ridge lying in front of this prominence becomes the muscle which runs from the funnel to the nuchal cartilage; the posterior part (which lies behind the rudiment of the visceral dome and mantle) forms the paired rudiment of the funnel itself. Between the two rudiments of the funnel, two other prominences rise symmetrically which are the rudiments of the gills. A pit in the centre of the rudiment of the visceral dome indicates the rudiment of a shell gland.