Which statement is true about mollusks?

Which statement is true about mollusks?

• A. They are the second largest phylum of animals.
• B. They have no circulatory system.
• C. All mollusks have open circulatory systems.
• D. Only gastropods have a closed circulatory system.

Answer: (A)

Mollusks are tested here for their place in animal diversity, specifically how many species belong to this group. The true statement reflects how large and varied the mollusk lineage is. Mollusca includes a vast range of animals—snails, clams, mussels, octopuses, squids, nautiluses, and more—occupying marine, freshwater, and terrestrial environments. Because of this enormous diversity, the phylum Mollusca is traditionally regarded as the second-largest animal phylum by described species, after Arthropoda. The other options misstate circulatory traits. Mollusks do have circulatory systems, but the type varies: many have open circulatory systems, where blood-like fluid Bathes internal tissues, while cephalopods such as squids and octopuses have closed circulatory systems with vessels. So it isn’t correct to say all mollusks have open systems, nor that only gastropods have closed systems, or that they lack a circulatory system at all.

Mollusks are tested here for their place in animal diversity, specifically how many species belong to this group. The true statement reflects how large and varied the mollusk lineage is. Mollusca includes a vast range of animals—snails, clams, mussels, octopuses, squids, nautiluses, and more—occupying marine, freshwater, and terrestrial environments. Because of this enormous diversity, the phylum Mollusca is traditionally regarded as the second-largest animal phylum by described species, after Arthropoda.

The other options misstate circulatory traits. Mollusks do have circulatory systems, but the type varies: many have open circulatory systems, where blood-like fluid Bathes internal tissues, while cephalopods such as squids and octopuses have closed circulatory systems with vessels. So it isn’t correct to say all mollusks have open systems, nor that only gastropods have closed systems, or that they lack a circulatory system at all.