The genes present in the construction of the embryo to develop into the mouth in the flatworms are similar to the genes present in the mouth formation in deuterostomes and protostomes. A sister clade to the Bilateral animals is the Acoelomorpha and these organisms have one mouth that directly passes into the gut without any anus. However, recent researches suggest that the formation of mouth in the protostome is less likely to happen in the way that we thought. Previously, it was thought that the protostomes have the blastopore that develops into the mouth and that the anus was generated later when the gut started to tunnel inside the embryo. On the other hand, the gut usually tunnels inside the embryo till it reaches the other pole, thereby forming a hole that develops into the mouth. The original dent in the deuterostomes develops into the anus. There is a hollow nerve cord in these organismsĮmbryological origin of mouth and anus from the blastopore: The blastopore develops into a part of the gut which forms the mouth Indeterminate cleavage is exhibited by the embryo There is a solid ventral cord in these organisms The blastopore develops into a part of the gut which forms the anus At the embryonic level, the difference between these two clades is given as follows:ĭeterminate cleavage is exhibited by the embryo In protostomes, the blastopore develops into the mouth, and in deuterostome, it develops into the anus. The primary difference between the protostomes and the deuterostomes is in the embryonic development of blastopore. In between these two layers, there is a mesoderm which develops into muscles and connective tissues. On the exterior portion, the ectoderm is formed that later develops into hair, skin, and the nervous system. This forms the inner layer known as endoderm that later develops into a digestive system. Cells inside the blastopore travel inward till they reach the opposite pole of the blastula. During the process of gastrulation, a notch like structure emerges from the blastula and is known as a blastopore. In triploblastic animals, around three germ layers are found.

At a point in the development, the gastrulation process begins which results in the germ layer formation. This is the precursor structure to form the blastula. When multiple cells are generated, the cell layer is known as the blastoderm and it encircles a yolk-filled cavity known as blastocoel. During this process, the cleavage lines emerge at an angle so that the blastomere assemble themselves in a spiral shape, rather than appearing as a parallel line on the poles. A spiral cleavage pattern is exhibited by the protostomes. The cleavage pattern is one of the basic developmental differences between the deuterostomes and the protostomes. This entire zygote containing two poles later divides entirely in the process known as cleavage to create a ball containing dense blastomere cells and this structure is known as a morula. This zygote structure is split on its axis to develop two poles which is the vegetal pole that is present at the bottom of the animal pole which is situated at the top. In the development of the embryo, an egg and sperm usually fuse to develop into a zygote.

Definition blastopore