Etymologically from the Greek protos = primitive, first; sotoma = mouth, are nothing more than beings whose blastopore occurs after the completion of embryonic development, performing the role of the mouth.
“But what is the blastospore?”, You must be wondering. In embryology it is an extremity that acts as a means of communication in the embryonic phase, putting the digestive cavity in contact with the external one. The blastospore forms in the embryonic period of the gastrula, the stage when cell differentiation begins. Later, another extremity may appear, also during embryonic formation.
Depending on the group to which the animal belongs, this orifice may first perform the mouth function – as is the case with protostomiums – or initially act as the body’s anus – in the case of deuterostomies.
Also during the embryonic formation process, the protostomial animals develop an opening that has the function of anus, located at the height of the opposite end of the arch.
Contrary to the process that occurs in the most evolved beings, these classified as deuterostomies, the blastopore, initially with the function of the mouth, in the protostomium group can be found in organisms such as worms, mollusks and arthropods.
After these stages, the embryonic development of protostomic animals moves to the phase of organogenesis, which is characterized by the process of distinguishing organs from the embryonic leaflets generated in gastrulation and whose initial stage is called neurulation.
After the neurulation phase is completed, the embryonic leaflets remain in a differentiation process, giving rise to the specialized tissues of the adult.
Main characteristics of protostomes
- Cleavage – has a spiral shape
- Blastóporo – originates the mouth first
- Celoma formation – schizocelia
- Mesoderm – this derives from the mesentoblast