animals are classified as triploblastic if their developing embryo possesses a third germinal layer, the mesoderm, situated between the ectoderm and endoderm . The phylum Platyhelminthes, which includes flatworms, is identified as the first group of animals to exhibit this triploblastic organisation . In contrast, sponges (Porifera) are primitive multicellular animals with a cellular level of organisation . Ctenophores and coelenterates (a group that includes corals) are described as diploblastic, meaning they have only two embryonic layers separated by an undifferentiated mesoglea . This specific question was featured in the AIPMT PRE 2010 examination .