former taxonomy:
Class: GASTROPODA  Cuvier, 1797
Subclass: OPISTHOBRANCHIA  Milne-Edwards, 1848
Order: NUDIBRANCHIA  Cuvier, 1817

on the recent taxonomy see WoRMS:
MolluscaBase eds. (2022). Spurilla  Bergh, 1864. Accessed through:
World Register of Marine Species
at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=137636 on 2022-05-08
-