Just a tip for Unknownithologists when dealing with placeholders or inactive taxon (in case you don’t already know) 
I tend to find inactives entries when I am trying to clean up the Unknowns and State of Matter project.
I will do a species search on GBIF for species that were selected by the Observer but do not show up in the iNat database or are inactive. GBIF will often have the synonym, basionym, or accepted taxon listed.
World Register of Marine Species (WoRMS) is also a good source for accepted and unaccepted.
This can be helpful in pointing the identification in the right direction although I tend to back off from species if I am unfamiliar.