The most distinguishing feature of these invertebrates is their flat body. As the body does not have any cavity, they are flat. The body is also not segmented and they do not have specialized systems. Around eighty percent of the flatworms are parasitic in nature, while a few free-form flatworms are also present.

Platyhelminthes and Nematoda are two invertebrate animal phyla. Platyhelminthes consists of flatworms whereas Nematoda consists of roundworms. The main difference between Platyhelminthes and Nematoda is the anatomical structure of the body of each invertebrate.

Nematodes have an unsegmented body whereas annelids are metamerically segmented. Nematodes are pseudocoelomate, whereas annelids have a true coelom. Nematodes are dioecious, i.e. sexes are separate.

Annelids are segmented worms whereas roundworms are not segmented. Further, annelids have a true coelom while roundworms have a pseudocoelom. This means annelids have a well-developed mesoderm while roundworms lack a mesoderm. Annelids and roundworms are invertebrates with elongated bodies.

Annelids are segmented worms, so why aren’t they grouped together with the flatworms and roundworms? Because annelids are actually more closely related to species within the mollusk phylum than they are to their worm cousins in the flatworm and roundworm phyla.

Segmented worms is a common name used for Annelida. In Latin, Annelida is used to describe “little rings”. The body of the organisms of this group is segmented. It seems like numerous little rings are fused or joined together.

Annelids show the presence of a true coelom, derived from embryonic mesoderm and protostomy. Hence, they are the most advanced worms. A well-developed and complete digestive system is present in earthworms (oligochaetes) with a mouth, muscular pharynx, esophagus, crop, and gizzard being present.

The Annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms. They also have parapodia for locomotion. Most textbooks still use the traditional division into polychaetes (almost all marine), oligochaetes (which include earthworms) and leech-like species.

The great advantage of such segmentation is the evolutionary flexibility it offers—a small change in an existing segment can produce a new kind of segment with a different function. Thus, some segments are modified for reproduction, some for feeding, and others for eliminating wastes.

Segmentation in the human nervous system. Segmentation is the physical characteristic by which the human body is divided into repeating subunits called segments arranged along a longitudinal axis. In humans, the segmentation characteristic observed in the nervous system is of biological and evolutionary significance.

Segmentation of the body plan is important for allowing free movement and development of certain body parts. It also allows for regeneration in specific individuals.

The annelids include earthworms, polychaete worms, and leeches. All members of the group are to some extent segmented, in other words, made up of segments that are formed by subdivisions that partially transect the body cavity. Segmentation is also called metamerism. The internal organs of annelids are well developed.

Some horses’ navicular bones segmented into two or three parts, which can be detrimental to health and welfare. This segmentation isn’t the result of injury or wear, though; the horses are born this way. And the effects are detrimental to the horse’s health, performance, and welfare.

Starfish shows radial symmetry, where symmetrical arrangement of parts of an organism around a single main axis, so that the organism can be divided into similar halves by any plane that contains the main axis. Therefore segmentation of body is not represented.

Starfish shows radial symmetry, where symmetrical arrangement of parts of an organism around a single main axis, so that the organism can be divided into similar halves by any plane that contains the main axis. Therefore segmentation of body is not represented. Hence, option C is correct.

Amphibians have segmented bodies. This is because amphibians are in the phylum chordata and chordates have segmented bodies. however the frog does not have segmentation. The frog has bilateral symmetry.

Complete answer: – In some Animals, the body is externally and internally divided into segments with the serial repetition of at least some organs. For example in earthworm, the body shows this pattern called metameric segmentation and the phenomenon is called metamerism. This phenomenon is absent in hydra.

As Cnidaria they have stinging cells on their tentacles. They are hydrozoa, and belong to the same order as other polyps. Most Hydra are microscopic in size. Hydras can be found in almost any unpolluted body of water….Hydra (animal)

Metameric segmentation is most strongly marked in annelids in which the muscles, blood vessels and nerves etc. Metamerism is absent in echinoderms, molluscs and platyhelminthes.