Fig. 1

Schematic representation of fissiparous (a) and sexual (b) reproduction in planarians. a Fissiparous individuals do not develop the reproductive system and instead they reproduce by binary fission. After the fission process, the planarian stem cells or neoblasts (white dots) are recruited to the wound and regenerate the missing part of the individual through proliferation and differentiation. b Sexual individuals are hermaphrodites that show the full set of male (blue) and female (red) reproductive organs. In this case, the differentiated germ cells located in the ovaries and in the testes are the responsible for gamete production, while neoblasts of sexual individuals (white dots) do not participate in the reproductive process. After the cross-fertilization by the exchange of sperm, several embryos are encapsulated into a cocoon, which will hatch after few weeks from the oviposition