Planarians are hermaphrodites: they have both a male and a female reproductive system. However, there is no self-fertilization. Planarians are first male, then female. Each idividual produces 4 to 6 eggs which it deposits in a yellow to brown cocoon, often attached to the substrate by a small peduncle. The larvae then emerge when environmental conditions are less hostile.
If one part of its body is cut, the planaria will recreate the missing part in its entirety, regardless of the size of the body parts or the number of parts cut: each one will regenerate. Each regenerated part then forms a clone of the original planarian, with the same genetic code. However, the clones do not have the same size: it can decrease compared to the initial planarian.
[FR] « La biologie du développement », Jonathan Slack, traduction de la première édition anglaise par Thierry Lesnik, Révision scientifique de Etienne Brachet, éditions de boeck
« The power of regeneration and the stem-cell kingdom: freshwater planarians (Platyhelminthes) », Salo E., BioEssays, 2006
Grohme, M., Schloissnig, S., Rozanski, A. et al. The genome of Schmidtea mediterranea and the evolution of core cellular mechanisms. Nature 554, 56–61 (2018). https://doi.org/10.1038/nature25473