May 22 is the International Day for Biological Diversity. This year the theme is marine biodiversity.

International Day for Biological Diversity was created by the United Nations to increase the understanding and awareness of biodiversity issues. 

Images above from the Biodiversity Heritage Library (Smithsonian Libraries is just one of the many libraries that contribute to this collection, this item comes from our friends at the Museum of Comparative Zoology at Harvard.) The volume is entitled An attempt towards a natural history of the polype. Polyps belong to the phylum Cnidaria, which  includes

many charismatic organisms such as hydras, sea fans, jellyfishes, sea anemones, corals, and the Portuguese man-of-war. Cnidarians all have some type of specialized stinging cell organelle. Cnidarians’ bodies typically take one of two forms: the polyp or the medusa. While the polyp form is adapted for a sedentary or sessile lifestyle, the medusa form is adapted for floating or free-swimming. Sea anemones and corals (class Anthoza) are all polyps.  (quote from )