True nucleus is absent in
(1) Anabaena is prokaryotic blue-green alga showing no true nucleus and membrane bound organelles. Rather a nucleoid region containing genetic material is present in the cytoplasm. The other cells of Mucor, Vaucheria and Volvox belongs to eukaryotic fungi and algae.
An organised nucleus or true nucleus is present in all eukaryotic cells. It is differentiated into nuclear envelope, chromatin, one or more nucleoli and nucleoplasm. These cell also contain membrane bound organelles e.g. mitochondria, Golgi complex.