Difference Between Diploblastic and Triploblastic

Main Difference – Diploblastic vs Triploblastic

Diploblastic and triploblastic refer to two different types of blastula stages. The primary layer of cells, formed during the embryogenesis is referred to as the germ layer. In vertebrates, three germ layers can be generally identified in the gastrula; they are endoderm, mesoderm and the ectoderm. Animals with a more complex structure than a sponge (eumetazoans) however produce two or three germ layers. Radially symmetric animals are diploblastic. They produce only two germ layers: endoderm and the ectoderm. Bilaterally symmetric animals are triploblastic. They produce the three germ layers: endoderm, ectoderm and the mesoderm. The key difference between diploblastic and triploblastic animals is that diploblastic animals produce two germ layers excluding mesoderm and triploblastic animals produce all three germ layers.

This article explains,

1. What is Diploblastic
      – Definition, Features, Examples
2. What is Triploblastic
      – Definition, Features, Examples
3. What is the difference between Diploblastic and Triploblastic

What is Diploblastic

During gastrulation, diploblastic organisms form a gastrula which consists of two primary germ layers. These two germ layers are composed of endoderm and ectoderm but not mesoderm. Endoderm gives rise to true tissues combining with the gut. On the other hand, ectoderm gives rises to epidermis, nervous tissue and nephridia. Since diploblastic animals are lacking a mesoderm, they cannot generate body cavities. However, a non-living layer exists in between endoderm and ectoderm. This layer is often gelatinous and is referred to as mesoglea. Mesoglea helps to protect the body and lines the gut.

Diploblastic animals possess radial symmetry. Cnidaria and Ctenophora are considered as diploblastic. Jellyfish, comb jellies, corals and sea anemones are the examples of diploblastic animals.

Figure 1: Diploblastic Animal’s Gastrula

What is Triploblastic

Triploblastic organisms form all three primary germ layers – endoderm, ectoderm and mesoderm – during the gastrulation of the blastula. Mesoderm development is the characteristic feature in triploblastic animals. Mesodermal cells differentiate through the interactions of both ectodermal and endodermal cells. Coelom is developed from the mesoderm. Inside the coelom, freely moving organs are formed, providing protection against shocks by fluid cushions. These organs can grow and develop without the aid of the body wall. Mesoderm forms muscle, bone, connective tissues, circulatory system, notochord, etc. Other than that, endoderm develops into lungs, stomach, colon, liver, urinary bladder, etc. Ectoderm develops into epidermis, hair, eye lens, brain, spinal cord, etc.

All animals from flatworms to human are triploblastic. They belong to the clade: Bilateria and possess bilateral symmetry. Triploblastic animals are further divided into sections such as acoelomates, eucoelomates and pseudocoelomates. Acoelomates are lacking a coelom whereas eucoelomates consist of a true coelom. Pseudocoelomates are composed of a false coelom. Eucoelomates can be again divided into two sections: protostomes and deuterostomes. Protostomes develop the mouth from the blastopore whereas the deuterostomes develop the anal opening from the blastopore. It is believed that diploblastic animals gave rise to triploblastic animals around 580 to 650 million years ago.

Figure 2: Differentiation of Three Germ Layers

Difference Between Diploblastic And Triploblastic

Definition

Diploblastic: Diploblastic animals produce two primary germ layers, endoderm and ectoderm during gastrulation.

Triploblastic: Triploblastic animals produce three primary germ layers, endoderm, ectoderm and the mesoderm.

Biological Symmetry

Diploblastic: Diploblastic animals are radially symmetric.

Triploblastic: Triploblastic animals are bilaterally symmetric.

Mesoderm Development

Diploblastic: Diploblastic animals are lacking a mesoderm. In between endoderm and the ectoderm, mesoglea can be identified.

Triploblastic: Triploblastic animals develop a mesoderm.

Body Cavities

Diploblastic: Diploblastic animals do not have body cavities.

Triploblastic: Most triploblastic animals develop a body cavity, the coelom.

Endoderm Development

Diploblastic: Endoderm of the diploblastic animals forms true tissues and the gut.

Triploblastic: Endoderm of triploblastic animals forms lungs, stomach, colon, liver, urinary bladder, etc.

Ectoderm Development

Diploblastic: Ectoderm of the diploblastic animals forms epidermis, nervous tissue and nephridia.

Triploblastic: Ectoderm of the triploblastic animals forms epidermis, hair, eye lens, brain, spinal cord, etc.

Development of Organs

Diploblastic: Diploblastic animals do not have organs.

Triploblastic: Triploblastic animals have true organs such as heart, kidney and lungs.

Complexity of the Organism

Diploblastic: Diploblastic animals are not complex.

Triploblastic: Triploblastic animals are much complex than diploblastic animals.

Examples

Diploblastic: Jellyfish, comb jellies, corals and sea anemones are examples.

Triploblastic: Molluscs, worms, arthropods, echinodermata and vertebrates are examples.

Conclusion

Animals like sea sponges exhibit the simplest organisation, consisting only a single germ layer. Though they are composed of differentiated cells, they lack true tissue coordination. Diploblastic animals, on the other hand, exhibit an increased complexity than sponges, containing two germ layers, the ectoderm and endoderm. They are organised into recognisable tissues. But, triploblastic animals possess an additional germ layer, the mesoderm which they can develop complex organs in the body. Thus, the key difference between diploblastic and triploblastic animals is the type of the cleavage during embryonic development.

Reference:
1. “Germ layer”. Wikipedia, the free encyclopedia, 2017.. Accessed 17 Feb 2017
2. Myers P. Z. “Diploblasts and triploblasts”. Pharyngula, ScienceBlogs. 2006. Accessed 17 Feb 2017

Image Courtesy:
1. “Blastula”. By Abigail Pyne – Own work (PD-self) via Commons Wikimedia
2. “Location of the intermediate mesoderm nephrogenic cord”. By Davidson, A.J. – Davidson, A.J., Mouse kidney development (January 15, 2009), StemBook, ed. The Stem Cell Research Community, StemBook, doi/10.3824/stembook.1.34.1 (CC-BY-3.0) via Commons Wikimedia