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triploblastic Applied to animals in which the body wall is derived from three embryonic layers: the ectoderm mesoderm; and endoderm. All Animalia other than Coelenterata are triploblastic.
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n most animals, a third embryonic germ layer forms between the endoderm and the ectoderm. This is the mesoderm, and animals whose bodies develop from three layers of embryonic tissue are said to be triploblastic.
The triploblastic animals are collectively referred to as the Bilateria, because almost all of them are bilaterally-symmetrical. In these animals, mesoderm forms muscles and complex internal organs, so the Bilateria typically have much more complex bodies than do the Radiata.
A cross-section through the bodies of a typical vertebrate (Phylum Chordata) and a
typical insect (Phylum Arthropoda). Each body structure is formed from one
of the three embryonic germ layers. Ectoderm (blue) forms skin and the
central nervous system. Mesoderm (red) forms muscles, blood, and most of
the internal organs. Endoderm (yellow) forms most of the tissues associated
with the digestive system.
