The urchin uses its spines as feet; for it rests its weight on these, and then moving shifts from place to place.
Aristotle, The History of Animals
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.