SEA URCHIN GASTRULATION

SEA URCHIN GASTRULATION

6.            SEA URCHIN GASTRULATION

External type of fertilization is found in sea urchins. At the onset of gastrulation, primary mesenchyme cells undergo ingression. This inward migration of cell is due to change in their cell-adhesion properties. Archenteron (primitive gut) get the form by primary invagination of vegetal plate bearing blastopore. Due to the changes in the shape of cells in the vegetal plate primary invagination occur. Elongation of the archenteron across the blastocoels occurs due to secondary invagination, where it attaches near the animal pole of the embryo.

Involvement of formation of filopodia during secondary invagination, which gets extended by the secondary mesenchyme cells situated at the tip of the archenteron. Where archenteron meets with ectoderm leads to mouth formation. Blastoderm form anus of the mature animal. Mesenchyme cells will form mesoderm. Involvement of convergent extension also occurs during secondary invagination.  Secondary invagination is thought to involve filopodia extended by the secondary mesenchyme cells located at the tip of the archenteron. Secondary invagination also involves a convergent extension.


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