Final answer:
The statement is false, as not all organisms within the Phylum Mollusca have shells. The diversity of the mollusks includes both shelled and shell-less species, like squid and octopus.
Step-by-step explanation:
The statement that only organisms with shells are found in the Phylum Mollusca is false. Although many mollusks such as clams, mussels, and oysters do have shells for protection, there are also mollusks that do not have visible external shells. For instance, the class Cephalopoda, which includes squid and octopus, features species where the shell is either internal, reduced, or completely absent.
The phylum Mollusca encompasses a diverse range of organisms, with varying forms and adaptations. For example, the classes Caudofoveata and Solenogastres consist of shell-less, worm-like animals. Overall, mollusks are characterized by a muscular foot and a mantle, which secretes the shell in many but not all species. They also have a radula, a specialized feeding organ, but even this feature may not be present in all classes. Thus, Mollusca is a phylum of significant diversity both in form and presence of shells.