This is one of my favorite images, made when I was a graduate student in David McClay's laboratory at Duke University. My thesis research was on sea urchin primary mesenchyme cells, which make the larval calcium carbonate skeleton. I was fascinated by a paper published in 1975 by Kayo Okazaki, where she showed that cells isolated from a sixteen-cell-stage sea urchin embryo will divide, differentiate, and secrete larval skeletal rods without the presence of the rest of the embryo. I immediately had to repeat her experiments, and soon had these cells crawling on the bottom of a petri dish, synthesizing long spicules. One day I looked at the dish and was delighted to see that the cells had produced spicules that formed into a letter "R". The hunt was on to find other letters of the alphabet, and I was able to find a good "F" to help form the image above, where "my" sea urchin cells spelled out my initials.
For more info, see Okazaki, K. 1975. Spicule formation by isolated micromeres of the sea urchin embryo. Amer. Zool. 15:567-581.