Using the example of the structural features of flat, round and annelid worms, list the signs

Using the example of the structural features of flat, round and annelid worms, list the signs of the complication of the organization of animals?

Representatives of the types Flatworms, roundworms and annelids are a good example of the complexity of the structure of animals in the course of evolution. Although representatives of these three types have a number of similarities, there are many differences between them associated with complication.

Body cavity and internal structure
Flatworms are devoid of body cavities (the parenchyma is located between the organs); round – have a primary body cavity. It has no walls of its own. In annelids, there is a secondary cavity, which, firstly, has its own walls, and secondly, it is divided into segments (if the integrity of the body is violated, the cavity fluid will flow out only from one segment, and not from the entire cavity). Digestive system: in flatworms, it ends blindly (there is no anus, so excrement is thrown out through the mouth). In roundworms, the anus also appears. It is also found in annelids. Therefore, representatives of the last two types do not have to throw excrement through the mouth.

The circulatory system in representatives of the first two types is not represented (the movement of nutrients occurs through the parenchyma in the former and through the primary body cavity in the latter). But annelids have it. Moreover, they have a closed circulatory system. True, they have no heart; its function is performed by several vessels with especially powerful thickened walls, located segmentally in the anterior part of the body.

Features of the nervous system
It is present in all three types of worms, but each has its own characteristics:

in flatworms – from the paired ganglion, as well as several nerve trunks extending from it with bridges;
in roundworms – from the periopharyngeal ring and two nerve trunks (dorsal and abdominal);
in annelids, from the periopharyngeal ring and the abdominal nerve ladder extending from it (from the paired ganglia, between which there are nerve cords).
Thus, the features of the organization of the three considered types of worms demonstrate a steady increase in the complexity of the organization of these animals in the course of evolutionary development.

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