Where does “Echiura” come from?

Echiura (Translingual) comes from Ancient Greek οὐρά, from Proto-Indo-European ors- — tail.

Ancestry of “Echiura”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	οὐρά	the tail, of a lion, dog etc; the rear-guard,...
2	Proto-Indo-European	ors-	tail

Echiura — Etymology, Origin & Word History | Etymology Explorer