Questions about nested Hierarchy

[Paraleptopecten (Timothy Campbell)]

How, precisely, does something else explain this better than evolution?

@Paraleptopecten

An example of the type of gene change used for phylogeny:

Nearly all members (that have been checked) of Buccinoidea, Muricidae, Olivoidea, “Turbinelloidea”, and Conoidea share TTTACTGGT GC GTCGGCTGCGAGCGT in the earlier part of their 28S genes. Most other caenogastropods have a CG instead of the bold GC.

The gene is producing part of nuclear ribosomes in pretty much all animals. Why does that change only appear in a large subset of gastropods that also share a siphon, fairly frequent large size, have similar radular morphologies, and are macrocarnivors (except for columbellids), if they are not actually related?

I could (if I had time) find a few dozen more of these in the sequences which I have downloaded.