Diploblastic vs Triploblastic
Depending on the primary germ layers present in blastula stage of organisms, they can be categorized mainly into two groups; diploblastic and triploblastic. The basic three germinal layers are ectoderm, mesoderm and endoderm. Ectoderm and endoderm layers are common to both diploblastic and triploblastic animals, while mesoderm is only found in triploblastic animals. In addition to these two types, there is one group of animals, sponges, which have a single undifferentiated layer, hence called monoblastic.
Diploblastic organisms have only two primary germ layers in their blastula; namely, endoderm and ectoderm. The inner layer, endoderm, gives rise to tissues associated with gut and associated glands while the outer layer, ectoderm, gives rise to covering tissues like epidermis. Animals in phyla Cnidaria and Ctenophora belong to this group. Cnidarians include jellyfish, corals, sea pens, sea anemones etc., and ctenophores include comb jellies. These simple, primitive metazoans basically lack body cavities and true organs.
Most of the metazoans develop three primary germ layers in their blastula, hence referred to as triploblastic animals. The three primary germ layers are ectoderm, mesoderm, and endoderm. Ectoderm basically gives rise to the epidermis and may also give rise to sensory organs and parts of the nervous system. Mesoderm forms mainly muscles, connective tissues, blood vessels, epithelial lining of interior cavities, certain excretory organs, and skeletal elements. Endoderm gives rise to parts of gastrointestinal tracts, respiratory tract, parts of endocrine glands and organs, and auditory system. Triploblastic animals have complex body structures including coelom or true body cavity and true organs. However, certain triploblastic animals secondarily lost their body cavities, hence called acoelomates. In certain triploblastic animals like acoelomates, mesoderm and mesenchyme are found in between ectoderm and endoderm. Tripoloblastic animals with hemocoel have mesoderm and hemocoel in between ectoderm and endoderm and, in triploblastic coelomates, mesoderm and coelom are found in between ectoderm and endoderm.
What is the difference between Diploblastic and Triploblastic?
• Diploblastic animals are primitive metazoans, whereas triploblastic animals include advanced metazoans.
• Diploblastic animals have two germ layers including ectoderm and endoderm while triploblastic animals have three germ layers including ectoderm, mesoderm, and endoderm.
• Diploblastic animals include Cnidarians and Ctenophores, while triploblastic animals include worms, arthropods, echinoderms, molluscs, and vertebrates.
• In certain diploblastic animals, mesoglea is found in between ectoderm and endoderm whereas, in triploblastic animals, mesoderm separates the ectoderm and endoderm.
• It is believed that triploblastic animals have evolved from diploblastic animals around 580 to 650 million years ago.
• Unlike triptoblastic animals, diploblastic animals lack body cavities and true organs (certain triploblastic animals like acoelomates have become secondarily simplified and lost their body cavities).