FURTHER PHYLOGENETIC CONSIDERATIONS

FURTHER PHYLOGENETIC CONSIDERATIONS

There are different views about the evolution of platyhelminthes:


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  1. Zoologists believe that the platyhelminthes body form is central to animal evolution. They believe that an ancestral flatworm was similar to turbellarians. The cladogram of platyhelminthes unites the Monogenea, Trematoda and Cestoidea.
  2. Recent molecular data suggest that the acoelomate flatworms are not members the Phylum Platyhelminthes. They are very close to the first ancestral bilateral Animals.
  3. More evidence links the parasitic flatworms to ancient, free-living ancestors. The free-living and parasitic ways of life formed in the Cambrian period, 600 million years ago. The first flatworm parasites were associated with primitive molluscs, arthropods and echinoderms. They later acquired the vertebrate hosts and complex life cycles.
  4. The gastrotriches show some distant relationships to the acoelomates. For example. many gastrotriches lack a body cavity. They are Monoecious and small. Their ventral cilia were derived from the same ancestral sources as those of the turbellarians flatworms.

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