"Hox genes originated very early in evolution and are therefore present in many animals, from corals to humans," says Andreas Wanninger from the Department of Integrative Zoology at the University of Vienna. They are usually read chronologically in the development of the animals and spatially from front to back in exactly the same order in which they are applied to the genetic material. This connection is called "collinear expression". One exception, however, seemed to be the molluscs: they did not find this precise pattern, but instead saw that the Hox genes are active in certain organs in which they are involved.

"Staggered Hox expression is more widespread among molluscs than previously appreciated" Tim Wollesen, Sonia Victoria Rodríguez Monje, André Luiz de Oliveira, Andreas Wanninger). In:  "Proceedings B" der Royal Society. DOI: 10.1098/rspb.2018.1513