Jake Young is a 
It's mad, I tell you, madddd! Mad scientists these days. Always going around saying, "Hey, you know how that animal could be better? If it had another head. Muahahaha!"
Anyway, the (possibly mad) scientists Wolfgang Jakob and Bernd Schierwater wanted to know more about the genes that determine the body plan of multicellular organisms. In mammals, these genes are called Hox genes, and in organisms that have circular symmetry like jellyfish they are called Cnox genes. We know that these genes broadly pattern the body plan of multicellular organisms because in a variety of settings if you knock out these genes they result in some weird -- and slightly grotesque -- body forms.
Such is what Jakob and Schierwater did with a species of jellyfish called European hydromedusa or Eleutheria dichotoma. They used a technique called RNA interference to selectively down-regulate different Cnox genes to see what the results would be for the body form. (Here is the paper in PLoS One.)
The figure below shows some of their data:
The top row lists the particular Cnox gene that they knocked down-regulated. The bottom row describes what happened.
My suspicion is that didn't in and of itself blow your skirt up. However, this is interesting for two reasons. One, in order to understand the function of Hox genes it is often easier to look at creatures that are more easy to manipulate and that are more likely to actually be born if they have developmental abnormalities of this severity. (Most mammals are not viable when Hox genes are knocked out.) Two, looking at jellyfish says some interesting things about points at which evolution diverged. Jellyfish have a completely different body plan than other animals -- circular as opposed to segmental. However, if we were to find that Cnox and Hox genes are related in both structure and function despite this difference in result, this would strongly suggest that the two genes diverges in a common ancestor long, long ago.
It might also go a long way to explaining stuff like this poor chap:
He has the dubious honor of being in the Freaks of Nature section on LiveScience. Animals like this one are sometimes born in the wild, but it is rare that they actually survive long enough to be observed.
Hat-tip: LiveScience
