Based on the number of nucleus cells are of following types:- (i) Uninucleated, (ii) Binucleated, and (iii) Multinucleated
Generally, eukaryotic cells contain at least one nucleus except in mature phloem sieve tube elements and mature RBCs of mammals.
Dikaryotic or Binucleated:- Example - Paramoecium.
Multinucleated cells may be of the following types-
(a) Coenocytic cells:- These types of cells, are formed by free nuclear divisions. Example:- Phycomycetes fungi, Endosperm, Rhizopus (a member of Zygomycetes), Vaucheria (An alga), etc.
(b) Syncytium:- Syncytial condition is formed by the fusion of cells. Example:- Epidermis of nematodes, and striped muscles.
Size and shape of cells differ significantly. It may be the smallest cell of Mycoplasma(0.3micrometer) or largest cell of an ostrich egg. Acetabularia is the longest single-celled but uninucleated green alga. Among multicellular organisms, nerve cells are one of the most extended cells, while a human RBC is 7 micrometer in diameter. Cells also vary greatly in shapes which is mostly according to their function they perform. It may be polygonal, spherical, cuboidal, columnar, thread-like or even irregular.