Regarding alphabetical order or not, many classifications try to reflect history of life. While there *IS* a true history of life (parents have children, ancestors beget descendents) we don’t KNOW that truth, so we make our best
guess. With new information, we modify our guesse sand classifications change (it’s not just to annoy you).
When an ancestor gives rise to two lineages, many criteria could justify which lineage to list first. A convention many classification schemes use now is alphabetical order. But it’s just a convention. Your reason to use another order should
be fine.
However, be sure to reflect nested hierarchy. If ancestor A gave rise to descendent lineages B and C, and then B gave rise to D and E, then D and E could be listed in any order, but don’t put C BETWEEN D and E (if you want to depict ancestor-descendent
relationships) because C is from a different lineage.
D
B <
/ E
A <
\
C
For your taxa of interest, I checked Molluscabase for names of higher categories. Our current best guess is that the first Gastropoda (listed as a class) gave rise to several lineages; the TWO relevant here are Caenogastropoda and Heterobranchia
(as subclasses); Caenogastropoda gave rise to several, the ONE relevant is Littorinimorpha (as order) and Littorinimorpha gave rise to several, the TWO relevant are Rissooidea and Vermetoidea (as superfamilies), with Zebinidae in Rissooidea and Vermetidae
in Vermitoidea. Heterobranchia gave rise to several lineages, the ONE relevant is Tectipleura (as subterclass), which gave rise to several lineages, the TWO relevant are Aplysiida and Ellobiida (as orders), with Aplysiidae in Aplysiida and Ellobiidae in Ellobiida.
I left out some intervening categories, so don’t worry if you don’t see a particular taxonomic category listed.
Rissooidea --- Zebinidae
/
Caenogastropoda --- Littorinimorpha
/ \
/ Vermetoidea --- Vermetidae
/
Gastropod Aplysiida --- Aplysiidae
\ /
Heterobranchia --- Tectipleura
\
Ellobiida --- Ellobiidae
To reflect ancestor-descendent relationships, you can list Zebinidae and Vermetidae in any order, but they should be together and not mixed with Aplysiidae and Ellobiidae, which two can also be in any order but not mixed with Zebinidae
and Vermetidae. I think the following 8 arrangements are the only ones that preserve the ancestor-descendent relationships (A=Aplysiidae, etc.):
(1) A, E, V, Z; (2) A, E, Z, V; (3) E, A, V, Z; (4) E, A, Z, V; (5) V, Z, A, E; (6) V, Z, E, A; (7) Z, V, A, E; (8) Z, V, E, A.
Any of those orders should be acceptable. Choose the one most convenient for you.
Best wishes, -Tim-
Timothy A. Pearce, Ph.D., Assistant Curator, Section of Mollusks
Carnegie Museum of Natural History
4400 Forbes Ave, Pittsburgh, PA 15213-4080, USA
ph 412-622-1916; fax 412-622-8837; [log in to unmask]
https://carnegiemnh.org/research/mollusks-malacology/
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