The Collaborative International Dictionary of English v.0.48:

Monerula \Mo*ner"u*la\, n. [NL., dim. of moner. See Monera.]
   (Biol.)
   A germ in that stage of development in which its form is
   simply that of a non-nucleated mass of protoplasm. It
   precedes the one-celled germ. So called from its likeness to
   a moner. --Haeckel.
   [1913 Webster]