ˈsōməd.əˌblast noun
Etymology: somat- + -blast
1.
a. : a cleavage cell of an annelid worm that is the precursor of most of the trunk ectoderm, the nervous system, and the nephridia
b. : cleavage cells descended from the primary somatoblast cell of an annelid
2. : the outer layer of cells of the nematogen of a dicyemid mesozoan