Goose barnacles are a fun example, because they were used to claim that the goose was fish rather than fowl and hence it was the only meat to be allowed during lent.
Re:Is a Turtle an Animal or a Fish?
by stillbourne on Wednesday September 30, 2020 @12:18PM
(#24640383)
The catholic church also classified beaver as a fish for the same reason.
How many people know what Kingdom a barnacle, a sponge, coral, or kelp belongs to.