former taxonomy:
Class: GASTROPODA  Cuvier, 1797
Subclass: OPISTHOBRANCHIA  Milne-Edwards, 1848
Order: SACOGLOSSA  von Ihering, 1876

on the recent taxonomy see WoRMS:
MolluscaBase eds. (2020). Placida  Trinchese, 1876. Accessed through:
World Register of Marine Species
at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=138524 on 2020-10-06
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