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Triploblasts (from Latin - Gr. Tri ~ three and blastos ~ germ, bud) in the broader sense are tissue animals in which three germ layers develop from the blastula in the course of gastrulation . The three-seeded, i.e. triploblastic, embryo is called triploblast in the narrower sense. The three cotyledons are ectoderm , mesoderm, and endoderm .

Triploblasty (three-seeded leaves) is found in all animals that were originally bilaterally symmetrical and is evidently directly linked to the development of bilateralism. Dicotyledonousness (diploblasty), however, is found in the coelenterates , monocotyledonous in the tissue-less Metazoa and the Placozoon Trichoplax adhaerens .

The first evidence for a triploblast in the broader sense is Kimberella from the Ediacarium , a presumed ancestor of today's mollusks .

With regard to the presence of a body cavity formed from the mesoderm ( Coelom ), the triploblastic animals are divided into the not necessarily monophyletic groups of

Synapomorphies of triploblastic animals

  • Presence of a mesoderm
  • Bilaterally symmetrical construction plan, in some animals only in the larval stage
  • All synapses are mono-directional
  • Presence of a centralized nervous system


  • Werner A. Müller, Monika Hassel: Developmental Biology. 4th, completely revised Edition. Springer, Berlin et al. 2006, ISBN 3-540-24057-8 , pp. 254ff.
  • H. Philippe, A. Chenuil, A. Adoutte: Can the Cambrian explosion be inferred through molecular phylogeny? In: Development. (Supplement), 1994, p. IS25 ff.
  • Kevin J. Peterson, Mark A. McPeek, David AD Evans: Tempo and mode of early animal evolution: inferences from rocks, Hox, and molecular clocks. In: Paleobiology. 31 (2, Supplement), 2005, pp. 36-55.

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