Pinigrade or Pinnigrade: How To spell?
The word Pinigrade is misspelled against Pinnigrade, a noun meaning "An animal of the seal tribe, moving by short feet that serve as paddles."
Pinnigrade has double "nn" is mispronounced as "n"Remember double 'NN' in between the strings pi & igrade which should not be misspelled with single 'N'
Wrong Spelling:  pi-n-igrade  Correct Spelling:  pi-nn-igrade 
Find more wrongly spelled words of Pinnigrade to spell it well.