Nuclearia is a genus of nucleariid amoebae with filose pseudopodia and discoid mitochondrial cristae.

Nominal species treated as members of the genus include:

The type species is Nuclearia delicatula, which may adopt a spherical or a flattened body form.

There is considerable uncertainty as to the identity of species and genera, and this led to the inclusion in Nuclearia of taxa previously assigned to Astrodisculus, Nuclearella, Nuclearina, Heliosphaerium and Nucleosphaerium, and the diversity rendered to 9 clearly distinguishable species with the affinities of Astrodisculus araneiformis, A. minuta and A. marinus remaining unclear