villamontana.blogg.se - Protostome blastopore becomes

Protostomy is a condition in which the blastopore was retained as the bilaterian mouth, the anus developing as a secondary opening.

Amphistomy is a condition in which the tubular gut evolved from the sack-shaped gut through lateral blastopore closure, leaving mouth and anus.

The tubular gut of the bilateral animals evolved from the sack-shaped gut of the common ancestor.

The latest common ancestor of the eumetazoans (ctenophores and placozoans are not discussed here) was a gastrula-like organism, with a sac-shaped gut with a blastopore.

It is concluded that the tubular gut with mouth and anus most probably evolved through amphistomy. fate of the actual blastoporal opening fate of the tissues surrounding the blastoporal opening, studied both through cell-lineage and gene expression morphology and embryology of the central nervous systems and morphology of larval ciliary bands according to the trochaea theory. A recent review has discussed the most informative characters related to the blastopore fates, viz. Three theories for the evolution of the tubular gut prevail: (1) Protostomy in which the blastopore should become the mouth and the anus develop secondarily, (2) Deuterostomy in which the blastopore should become the anus and the mouth develop secondarily and (3) Amphistomy in which the blastopore should become divided into mouth and anus through fusion of the lateral blastopore lips.

Cell-lineage studies show that gastrulation through epiboly and invagination follow similar patterns with the cells of the blastopore rim bordering the cells which give rise to endo-mesoderm. The bilaterian tubular gut with mouth and anus is generally believed to have evolved from the sack-shaped gut of a gastrula-like organism.