Final answer:
Marine worms and mollusks share a closer evolutionary relationship based on similar larval stages, indicating a common ancestry. Both belong to the Lophotrochozoa clade, distinct from the Ecdysozoan clade. DNA evidence supports the revised relationships among these invertebrates.
Step-by-step explanation:
Based on the similarities in larval stages and other developmental characteristics, it can be inferred that marine worms (Annelida) and mollusks (Mollusca) have a closer evolutionary relationship than previously thought.
This inference is supported by the fact that both marine worms and mollusks go through the trochophore larval stage. This stage is critical because it is a shared developmental phase that indicates a common ancestry.
The phyla Mollusca and Annelida both belong to the Lophotrochozoa clade, which sets them apart from other invertebrate groups such as arthropods and nematodes, based on molecular evidence.
This evidence from DNA analysis has led to a revised view on the relationships among invertebrates, grouping annelids and mollusks closer together and away from the Ecdysozoa clade that includes nematodes and arthropods.
Therefore, the presence of similar larval stages suggests that these two groups of organisms may share a more recent common ancestor, which they do not share with groups like arthropods.
Additionally, it is important to remember that while developmental stages can help infer relationships, appearance alone can sometimes be deceiving due to convergent evolution, as seen in the unrelated barnacles and limpets which have similar shells due to environmental pressures rather than common ancestry.