Fruit flies and nematode worms have long been the workhorse of biology, for they share many genes with humans and can be bred with ease. In fact, the double helix shows that each of those laboratory stalwarts is less like us than was once assumed as for reasons quite unknown both have, on the long road from the Pre-Cambrian, lost even more inherited information than we ourselves have. As a result, each is left with a unique and diminished identity of its own and corals have more distinctly human genes than either of them.
The big step forward made by humans or flies compared to polyps is that we have an anus: every one of us, however eminent, is a tenametre tube through which food flows, for most of the time, in one direction. Hydra and its kin are in contrast mere sacs, obliged to suck in sustenance and throw out waste from a single hole.
Corals - Steve Jones