A mollusc and an annelid both show trochophore larvae in many species, but their adult body plans are very different. In an exam answer, the key reason is: (278)

Correct Answer: A

trochophore larva as a developmental link

The trochophore larva supports a developmental relationship between many molluscs and annelids. Adult molluscs have mantle, foot, and visceral mass, while annelids are segmented worms. This question is designed as a comparison-based item to reduce thin-content style repetition and improve conceptual depth.