What are diploblastic animals

Triploblasts (from lat.-gr.tri ~ three and blastos ~ Germ, bud) in the broader sense are tissue animals in which three cotyledons develop from the blastula in the course of gastrulation. The tricot, so triploblasticEmbryo is called triploblast in the narrower sense. The three cotyledons are ectoderm, mesoderm, and endoderm.

Triploblasty (Tricotyledon) is found in all originally bilaterally symmetrical animals 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 of 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

  • Acoelomata: Animals without coelom, only with mesoderm, for example flatworms
  • Pseudocoelomata: Animals with pseudocoel, for example the tube worms
  • Coelomata: Animals with real coelom, for example the chordates

Synapomorphies of triploblastic animals

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


  • Werner A. Müller, Monika Hassel: Developmental biology. 2005 4, ISBN 3540240578, pp. 254ff.
  • H. Philippe, A. Chenuil, A. Adoutte: Can the Cambrian explosion be inferred through molecular phylogeny? Development (Supplement), 1994, p. IS25 ff.
  • Kevin J. Peterson, Mark A. McPeek, David A. D. 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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