Ancalagon is a genus of worm known from the Cambrian Burgess Shale, and assigned to the Priapulids.[2] It also bears similarity to the hypothetical ancestor of a group of parasitic worms, the Acanthocephala.[2] Two specimens of Ancalagon (genus) are known from the Greater Phyllopod bed, where they comprise < 0.01% of the community.[3]

Along with the other Cambrian worms Ottoia, Selkirkia, Louisella, Fieldia, Scolecofurca, and Lecythioscopa, the organism may fall into a clade termed the archaeopriapulida, a stem group to the Priapulids proper.[4] However, the morphological similarity of these organisms to their modern cousins is remarkable, especially for the Burgess Shale.[5] A phylogenetic analysis does not provide a great deal of resolution to the relationships between these basal worms.[6]

The genus takes its name from the dragon Ancalagon the black (Which was so large when it died it crushed Thangorodrim - a humongous mountain that was created by Melkor) , who is featured in J.R.R. Tolkien's Middle-earth legendarium, in reference to the worm's strong row of hooks on its proboscis.

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