Triarthrus was an olenid trilobite. Its relatively long and broad thorax meant it was well endowed with gills. It needed to be, because it lived in deep, anoxic, sulphur-rich sediments. But housed in its gill structures were symbiotic bacteria that metabolised sulphur and released oxygen.
Triarthrus, that’s my moniker, olenimorph my style.
I live where other trilobites daren’t go.
It’s deep and dark and sulphurous, the atmosphere is vile,
But I just have to cope down here below.
I keep bacteria in my gills, the sulphur-eating sort
Who feed me all the oxygen they make.
But oh, this benthic lifestyle is so dull! I’ve often thought
My distant forebears made a big mistake.
I dream of being Olenoides, scavenging the sea;
A hunter – spiny, powerful, distinct.
But evolution’s locked me in this niche, as you can see.
’Twere better far, I think, to be extinct . . .