do arthropods have a coelom
The roundworm is a pseudocoelomate because it does not have a complete coelom within its mesoderm layer. In other words, its coelom is not completely lined by the mesoderm layer (blue). All complex animals have a true coelom, including the mollusks, annelids, arthropods, echinoderms and chordates.They have a true coelom that is completely lined by the mesoderm layer. The internal organs in a true coelom are more complex, and they are held in place by mesentaries.he roundworm is a pseudocoelomate because it does not have a complete coelom within its mesoderm layer. In other words, its coelom is not completely lined by the mesoderm layer (blue). All complex animals have a true coelom, including the mollusks, annelids, arthropods, echinoderms and chordates.