A Walk in the Woods
The sea urchin is a delicacy. Gourmets eat everything, by dipping pieces of bread into the open shell. Those in the know choose the iodized reproductive glands. But the most surprising element is the shell. A quick glance merely shows an impenetrable forest; the most one sees are moving prickles.
However, greater scrutiny reveals that these spines are not responsible for mobility; that function is performed by a highly specialized mechanism of hydraulic feet: small flexible stems, ending in suckers, emerge from the shell through hundreds of little holes. Inside the shell, these hollow stems fold into a bulb, and are ail linked together by vessels filled with water. When the bulb contracts it forces water into the elastic stems which then swell outwards, turning the forest into a flower. If the suckers hit an obstacle, they adhere to it. The stems then shorten, sending the water back into the bulb, the urchin being pulled in and held fast by the fixed suckers.
Magnification allows us to venture deeper into the woods. Around the spines, which by now look like Doric columns, we discover another smaller forest of bushes. These are pedicellariae: tiny organs which form a part of the urchin and are made of the same substance as the prickles. They present a calcareous stem, ending with three jaws which muscles open and close perpetually.
Some pedicellariae have long, thin jaws with an openwork design. Others, powerful and continuous, evoke snakes' heads. Others still, the cleaning pedicellariae, look like clovers; they clean the surface of the urchin and the fluting of the spines. Lastly, some have jaws set with poisonous glands and teeth with beveled edges, like hypodermic syringes. And the entire urchin is covered with cilia, except on the end of its spines...Perhaps these have been worn down...
Jean Painlevé,"Promenade en Forêt", ca. 1946.