Purple Sea Urchin
The urchin uses its spines as feet; for it rests its weight on these, and then moving shifts from place to place.
Spines have more uses than one would think. Sure, they defend against sea otters and the voracious stars. Ball-jointed, they swivel to catch pieces of floating algae for the shorter, two- fingered pedicellines to convey to the bottom-scraping mouth & its five sharp pyramids.
They are digging bars. A purple urchin can excavate a hollow into solid rock. If it starts too young, it may become stuck, entombed. Some never dig at all, & wander slow as time through the kelp forest.
The spines sharpen a kind of vision, too, like squinting eyelids bringing into focus the images collected by the pedicellines & the tube feet, which are furred with light-sensitive molecules. The more numerous a sea urchin’s spines, the sharper its vision — & yet it has no brain. It is all brain. And it lacks eyes because it is all eye, revolving in its self-made socket for as long as a century, risking death from the removal of a single spine, unable ever to shut.