diploblásticos

Diploblásticos are animals whose embryos develop from two primary germ layers: the ectoderm and the endoderm. They lack a true mesoderm, which in triploblastic animals gives rise to most muscles and many organs. This simple tissue organization underlies the basic body plans of diploblastic phyla.

During development, the two germ layers give rise to the epidermis (from ectoderm) and the gastrodermis lining the gut (from endoderm), with a jelly-like mesoglea between them in many species. Diploblastic animals typically exhibit radial or biradial symmetry and have a gastrovascular cavity that serves digestion and circulation rather than a through gut. They have tissues more than single cells but generally do not form true organs.

Major groups are the phyla Cnidaria (for example jellyfish, corals, sea anemones) and Ctenophora (comb jellies). The cnidarians often possess tentacles with cnidocytes and show life cycles alternating between polyp and medusa forms; ctenophores are free-swimming and use rows of ciliary plates for locomotion.

Evolutionary perspective: diploblastic organization is considered the more ancestral condition for multicellular animals; the emergence of a mesoderm in triploblastic lineages enabled greater organ complexity and body cavities. Studying diploblásticos sheds light on early animal evolution and the diversification of tissues.