Multiple choice Which of the following phyla have true body cavity? Porifera Coelenterata Nematoda Annelida Reveal answer Fill a bubble to check yourself D Correct answer Explanation Annelida are the first phylum to exhibit a true coelom (a fluid-filled cavity completely lined by mesoderm). Porifera, Coelenterata, and Nematoda are acoelomate or pseudocoelomate.