spicule vs spiculum

spicule

noun
  • A sharp, needle-like piece. 

  • A needle-like mating structure found only in male nematodes. 

  • A tiny glass flake formed during the manufacture of glass vials 

  • A small spike of flowers. 

  • A jet of matter ejected from the photosphere of the sun. 

  • Any of many needle-like crystalline structures that provide skeletal support in marine invertebrates like sponges. 

spiculum

noun
  • A sharp, needle-like structure, especially those making up the skeleton of a sponge. 

  • A thrusting javelin used by Romans that replaced the pilum in the late 3rd century. 

  • A sharp, pointed crystal, especially of ice. 

  • A small radial emission of gas seen in the chromosphere and corona of the sun. 

How often have the words spicule and spiculum occurred in a corpus of books? (source: Google Ngram Viewer )