What are the 3 germ layers of an animal embryo and what does each give rise to? Which animal phylum has only 2 of these germ areas?
There are three germ layers in an early embryo of an animal: ecto-, meso- and endo-derms: this is true for triploblastic animals. Animal phyla Porifera, Cnidaria, and Ctenophora are diploblastic, they develop only ectoderm and endoderm.
Ectoderm is the outermost layer of cells: while endoderm lines the primitive gut/'archenteron'.
Germ layers eventually give rise to all organs of the body.
Ectodermal organs are mainly: skin and nervous system.
Endodermal organs are: lungs, gastrointestinal tract, liver, pancreas.
Mesodermal tissues are: muscles, bones, blood, cartilage.