Classification of a specific cell type is often done through the use of microscopy (such as those from the cluster of differentiation family that are commonly used for this purpose in immunology).
This has led to the discovery of many new cell types in e.g. mouse cortex, hippocampus,[2] dorsal root ganglion[3] and spinal cord.
During development, somatic cells will become more specialized and form the three primary germ layers: ectoderm, mesoderm, and endoderm.
The simplest organism considered to have well defined cell types are some volvoceans, such as Volvox carteri, in which each organism is composed of distinct and interdependent cell populations, some somatic and some reproductive.
[9][10] A 2006 peer-reviewed article by Vickaryous and Hall listed 411 distinct human cell types.