Arthropoda: the most successful animal phylum
The third major line in the evolution of invertebrates was the development of the segmented bodies (Arthropoda) which evolved at a very early stage and are contemporary with the jellyfishfossil patterns found in Flinders, Australia. This group of animals shares one important feature with the molluscs, and that is a spherical larvae possessing a belt of cilia, whereas the echinoderm larvae have a twisted morphology with winding bands of cilia. This suggests that molluscs and arthropods evolved from flatworms (Platyhelminthes), with the echinoderms having an independent evolutionary line.
The blue crab (Callinectes sapidus) is an example of an arthropod
