Q. What is the major evolutionary novelty presented by annelids?
The main evolutionary novelty presented by the beings of the phylum Annelida is the coelom, the internal body cavity totally covered by mesoderm, a feature also present in arthropods, molluscs, chordates and echinoderms. acoelomate are Platyhelminthes and nematodes are pseudocoelomate (their internal cavity is partially covered by mesoderm).
Another significant evolutionary novelty of the annelids is the closed circulatory system.