When I worked as a marine biologist and went scuba diving, I saw many live sea urchins moving underwater using their suckered tube feet to grip the rocks. Urchins have a hard shell or test that persists after they die, when the five-rayed starry pattern is evident in urchins sold in coastal souvenir shops.
The structure of any macro subject should convey how to light it to the best advantage. Years after I bought a few sea urchin shells, I held one in my hand beside a reading lamp. As I rotated it, the light lit the inside via the basal hole and suddenly beamed out through the tiny rows of holes where the suckered feet emerge through the shell.
Within moments, I was in my studio, manipulating a fibre optics unit. The shot was taken by inserting one fibre-optic inside the basal opening to reveal the twin rows of brightly backlit holes in a 5-rayed pattern that is typical of many urchins and related starfish. Also visible, between the backlit holes, are rows of protuberances that form the bases of the spines’ ball and socket joints.
Today, small LED lights can be used as cheap substitutes for fibre optics.