Happy 27th birthday to my son, who brought me this sea urchin shell—packed in his backpack—all the way home from his recent trip to New Zealand! He knows that I have a fascination with drawing examples of radial symmetry in nature (often based upon multiples of 5), which I've previously posted about here.
Before I sat down to draw this "test" (which, I learned, is the proper terminology for a sea urchin shell), I was curious whether or not it was as perfectly round as it appeared to my eye. So, I printed out a little template of a circle the same diameter as the shell. I laid the shell over it on my lightbox, and...wow! Mother Nature never ceases to amaze.
Since the shell is composed of a beautiful almost monochromatic blue-grey-green palette, I ended up using a toned Strathmore charcoal paper (the smooth side) and only graphite and 2 Prismacolor pencils: Jade Green, and White Verithin. (Sorry for the uneven lighting; I was too lazy to scan, so I just shot this at my desk with my iPhone.)
As I examined the shell closely, I was curious about the texture of the surface, and did a little research—they're fascinating creatures! The raised bumps are where the spines had been attached with an ingenious ball-and-socket mechanism, and all of the tiny holes are where the soft tube feet once extended. What an amazing little structure!