Ernst Haeckel Hexacorallia Coral Postcard

Hexacorallia is a subclass of Anthozoa comprising approximately 4,300 species of aquatic organisms formed of polyps, generally with 6-fold symmetry. It includes all of the stony corals, most of which are colonial and reef-forming, as well as all sea anemones, tube anemones, and zoanthids, arranged within six extant orders.[1] The hexacorallia are distinguished from another subclass of Anthozoa, Octocorallia, in having six or fewer axes of symmetry in their body structure and only single rows[citation needed] of tentacles. These organisms are formed of individual soft polyps which in some species live in colonies and can secrete a calcite skeleton. As with all Cnidarians, these organisms have a complex life cycle including a motile planktonic phase and a later characteristic sessile phase. Hexacorallia also include the significant extinct orders of the rugose corals and tabulate Ernst Heinrich Philipp August Haeckel was a German biologist, naturalist, philosopher, physician, professor, marine biologist, and artist who discovered, described and named thousands of new species, mapped a genealogical tree relating all life forms, and coined many terms in biology, including anthropogeny, ecology, phylum, phylogeny, stem cell, and Protista. Haeckel promoted and popularised Charles Darwin's work in Germany and developed the influential but no longer widely held recapitulation theory ("ontogeny recapitulates phylogeny") claiming that an individual organism's biological development, or ontogeny, parallels and summarises its species' evolutionary development, or phylogeny. The published artwork of Haeckel includes over 100 detailed, multi-colour illustrations of animals and sea creatures (see: Kunstformen der Natur, "Art Forms of Nature"). As a philosopher, Ernst Haeckel wrote Die Welträtsel (1895–1899; in English: The Riddle of the Universe, 1901), the genesis for the term "world riddle" (Welträtsel); and Freedom in Science and Teaching to support teaching evolution.