Vicky:
Alphabetical order is just that - alphabetical.
Alphabetical order places Heterobranchia before Vetigastropoda; that is
not a "phylogenetic" placement. We can go on and on about this topic,
and there will be no consensus. At some point, you have to pick a
system and go with it. Be assured that whatever you pick, somebody will
tell you that you are wrong.
Bob
PS:
If you want the 2017 Bouchet et al. document, you can download it from
ResearchGate; Google "Bouchet nomenclator," and find the ResearchGate
entry. It is highly technical and still puts a lot of names in
alphabetical order.