A germ layer is a collection of cells, formed during animal embryogenesis.

Germ layers are only really pronounced in the vertebrates.

However, all animals more complex than sponges (eumetazoans and agnotozoans) produce two or three primary tissue layers (sometimes called primary germ layers).

Animals with radial symmetry, like cnidarians, produce two called ectoderm and endoderm, making them diploblastic.

Animals with bilateral symmetry produce a third layer in-between called mesoderm, making them triploblastic.

Germ layers will eventually give rise to all of an animal’s tissues and organs through a process called organogenesis..

For more information about the topic Germ layer, read the full article at Wikipedia.org, or see the following related articles:

How internal organs form — In animal development, organogenesis is the process by which the ectoderm, endoderm, and mesoderm develop into the internal organs of the organism. ...  > read more

Mammalian embryogenesis — Mammalian embryogenesis is the process of cell division and cellular differentiation which leads to the development of a mammalian embryo. A mammal ...  > read more

Epithelium — In zootomy, epithelium is a tissue composed of a layer of cells. Epithelium lines both the outside (skin) and the inside (e.g. intestine) of ...  > read more

Embryo — In organisms that reproduce sexually, once a sperm fertilizes an egg cell, the result is a cell called the zygote that has all the DNA of two ...  > read more

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