Here's why:

* The traditional classification hierarchy: The traditional classification system uses the following hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. There is no formal level called "Superregnum".

* Eukaryotes as a Domain: The most widely accepted system places eukaryotes (organisms with a nucleus) as a Domain, which is the highest taxonomic rank.

* Other taxonomic systems: Some alternative systems may use "superkingdom" as a rank above kingdom, but even then, it's not common to refer to Eukaryotes as a "superregnum".

Therefore, "superregnum Eukaryota" is not a standard or widely recognized term in biological classification.