Spontaneous ectopic head formation enables reversal of the body axis polarity in microscopic flatworms

In microscopic flatworms from the genus Stenostomum the new head and tail structures are inserted in the pre-existing body plan during the asexual process known as paratomy. Here, we report a spontaneously occurring developmental error that results in the formation of worms with double heads at opposite ends of their bodies, lacking posterior pole identity. The first part of the dataset includes confocal images of the normal and double head worms. The animals were stained with antibodies and phalloidin for morphology, as well as HCR in situ for visualization of the expression of head and tail molecular markers. We also demonstrate that the piece of the worm with ectopic head can survive, regenerate the tail on its previously anterior pole and resume asexual reproduction. The second part of the dataset includes microphotographs of two regeneration time series of fragments with an ectopic head - one that retained the ectopic head after amputation and one that resorbed it.