Which group is known for having a soft body that may or may not be protected by a shell?

Mollusks are a diverse group of invertebrates characterized by their soft bodies, which may be protected by a hard shell in some species but not in others. This group includes well-known organisms such as snails, clams, and octopuses. The defining feature of mollusks is their body structure, which generally consists of a muscular foot, a visceral mass containing internal organs, and a mantle that may secrete a shell.

The variability in shell presence among mollusks is significant; some, like snails and clams, have a prominent external shell, while others, such as octopuses and slugs, either lack a shell or have a very reduced one. This adaptability in shell development is part of what makes mollusks ecologically successful across various habitats, from oceans to freshwater and terrestrial environments.

In contrast, the other groups mentioned have distinct characteristics that do not align with having a soft body potentially covered by a shell. Arthropods have exoskeletons made of chitin, chordates possess a backbone and have more complex body structures, and cnidarians are characterized by their gelatinous bodies and lack true organs or complex tissues. Thus, the characteristics of mollusks distinctly fit the description