Which of the following phyla is the most diverse in terms of number of species? Annelida (segmented worms) O Arthropoda (arthropods) Chordata (chordates) Cnidaria (cnidarians) Echinodermata (echinoderms) Mollusca (molluscs) Nematoda (roundworms) Platyhelminthes (flatworms) O Porifera (sponges)