I bumped into Mayer et al. (2010) while hunting for reagents to use in an experiment I’m planning. The article is about segmentation (sort of), so I had to have a closer look, and man. Those pictures. Fluorescence and a good microscope can do wonders. This is what a velvet worm looks like in normal light (whole body shot of an unspecified peripatid by Geoff Gallice, Wikipedia, and portrait of Euperipatoides rowelli by András Keszei via EOL):
I think they are adorable and cuddly the way they are (apart from that hunting with slime bit), but they look simply gorgeous if you stick some glowing antibodies to them and start playing with a confocal ‘scope.
This is a fairly late-stage embryo of E. rowelli, the same guy waving its chubby leggies at you in the right-hand photo above. The green dots are cells that were copying their DNA when the baby was killed (all of the pictures below are from Mayer et al., of course):
These are younger embryos of the same species, with all their DNA labelled in blue and dividing cells labelled in red:
And these are embryos of another species from the same family as the unidentified guy from Wikipedia (colours are the same as above):
Seriously, there is something about the mystical glow of these images that always gets me. I think you could make almost anything look beautiful with a fluorescent marker and the right equipment. I know aesthetic appeal isn’t the primary aim of scientific imaging, but damn. Look at those alien creatures glowing with the light of the unknown.
In case you wondered, the point of the paper is that velvet worms lack a posterior growth zone. That means that when they develop their numerous segments, there isn’t a well-defined pool of cells at the rear of the embryo that divide to generate segment material. As you can see in all the red glow, cell division happens evenly all over the place. Why is this significant? Well, posterior growth zones were thought to be one of the characteristics that segmented animals might have inherited from their common ancestor. But Mayer and colleagues point out that the existence of a PGZ in the arthropod ancestor is dubious at best, and velvet worms (one of the closest living relatives of arthropods) also lack one, so maybe it’s kind of wrong to use the PGZ as an argument for the common ancestry of segmentation.
(There, that’s the science in a nutshell. Now I’ll just go back and admire the pretty glowy pictures some more :D)
Mayer G et al. (2010) Growth patterns in Onychophora (velvet worms): lack of a localised posterior proliferation zone. BMC Evolutionary Biology 10:339