@hsini_lin @neilmcdaniel is correct that Tritonia tetraquetra and Tochuina gigantea are two distinct species. Please provide the research or other justification that you are using to synonymize these two separate species. Otherwise, please read this paper for the most recent research on these two completely unrelated species Korshunova, T.; Martynov, A. (2020). Consolidated data on the phylogeny and evolution of the family Tritoniidae (Gastropoda: Nudibranchia) contribute to genera reassessment and clarify the taxonomic status of the neuroscience models Tritonia and Tochuina. PLOS ONE. 15(11): e0242103., available online at https://doi.org/10.1371/journal.pone.0242103.
Even the more recent paper that examines Tritonia tetraquetra found it to be a valid species Ekimova, I.; Valdés, Á.; Stanovova, M.; Mikhlina, A.; Antokhina, T.; Neretina, T.; Chichvarkhina, O.; Schepetov, D. (2021). Connected across the ocean: taxonomy and biogeography of deep-water Nudibranchia from the Northwest Pacific reveal trans-Pacific links and two undescribed species. Organisms Diversity & Evolution. DOI 10.1007/s13127-021-00526-8., available online at https://doi.org/10.1007/s13127-021-00526-8 [details]