Many species of marine ribbon worm have gained the power to regrow their heads — an unprecedented example of related animals independently mastering the trick of regeneration.
Eduardo Zattara at the Smithsonian Institution’s National Museum of Natural History in Washington DC and his colleagues cut off the heads of individuals from 22 species of ribbon worm and observed that 5 species sprouted new heads. The researchers also found published accounts of 3 other species with this ability.
The team’s analysis of the ribbon-worm family tree suggests that head replacement arose at least four times in separate worm lineages. The lineage of the species Lineus sanguineus evolved the ability to replace a missing head only 10 million to 15 million years ago, which is much more recently than other animals are known to have acquired the art of regeneration.
This means that L. sanguineus could provide a valuable model for understanding how regeneration evolves, the authors say.