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amphicoelous

British  
/ ˌæmfɪˈsiːləs /

adjective

  1. (of the vertebrae of most fishes and some amphibians) concave at the anterior and posterior ends

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of amphicoelous

C19: from amphi- + Greek koilos hollow