Technically? Nudis and sea slugs are both Opisthobranchs (backwards or rear gills), which is split into quite a few groups, one of which is Nudibranchs (naked gills). Sea slugs are any shell less (externally at any rate) gastropod mollusc while nudibranchs are a specific group noted for their uncovered gills. Yes, it is a bit pedantic ;']
Edward
Edward
