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The Pelecaniformes are an order of medium-sized and large waterbirds found worldwide.
The pelicans, shoebill and hamerkop form a clade within the order, with their next closest relatives being a clade containing the herons, ibises and spoonbills. 

Pelecaniformes    
  Threskiornithidae – ibises, spoonbills (36 species)
  Ardeidae – herons, bitterns (72 species)
  Balaenicipitidae – shoebill
  Scopidae – hamerkop
  Pelecanidae – pelicans (8 species)

The family Threskiornithidae, which belongs to the bird order Pelecaniformes, includes 36 species of large wading birds. 

Pelecanus: Greek pelekan, pelekanos pelican.

Threskiornis Greek threskeia religious worship (threskeuo to worship); ornis bird. 
The Sacred Ibis Threskiornis aethiopicus was venerated by the ancient Egyptians for its crescent-shaped bill and bright white plumage. They considered it to represent Thoth the moon god.