The role of Cnidaria in evolution and ecology

The recent setting of specific features of the Cnidaria into evolutionary and ecological frameworks suggests the centrality of this phylum in many fields of the life sciences. From an evolutionary point of view, the Cnidaria, with their diploblastic planulae, might represent the ancestral state of higher Metazoa in the light of a peramorphic origin of animal complexity from a simple, individual organism. Medusan development in the Hydroidomedusae via a medusaty nodule, furthermore, implies the formation of a third tissue layer (the muscle layer lining the subumbrellar cavity). Cnidarian polyps are diploblastic, whereas at least some of their medusae are triploblastic: the evolutionary enigma of the passage from a diplo- to a triploblastic organisation takes place every time hydrozoan polyps bud medusae! Cnidarian polyps have also the premises of the skeletal architecture of higher animals: their chitinous or carbonatic skeletons are similar to those of arthropods and vertebrates respectively. From an ecological point of view, the coelenterates probably play roles that are much more important than usually perceived. Both Cnidaria and Crenophora feed on the eggs and larvae of most benthic, planktonic and nektonic organisms and might be crucial (with a keystone role?) in maintaining biodiversity high, by feeding on potentially monopolising species. The efficiency of gelatinous predators becomes evident during periodic Outbreaks of their populations, with serious implications even on fisheries yields, demonstrating that their impact can be higher than ours!.