Paratomy is a form of asexual reproduction in animals where the organism splits in a plane perpendicular to the antero-posterior axis and the split is preceded by the "pregeneration" of the anterior structures in the posterior portion.
Budding can be considered to be similar to paratomy except that the body axes need not be aligned: the new head may grow toward the side or even point backward (e.g. Convolutriloba retrogemma an acoel flat worm).
[1][2] In animals that undergo fast paratomy a chain of zooids packed in a head to tail formation may develop.
Many oligochaete annelids,[3] acoelous turbellarians,[1] echinoderm larvae[4] and coelenterates[5] reproduce by this method.
This paper has a detailed description of the changes during paratomy.