A class of small, primitive marine worms that are considered to be among the most ancient annelids, or segmented worms.
From archi- (primitive, original) + Annelida (the phylum of segmented worms). Annelida comes from New Latin, from annellus (small ring), from Latin annulus (ring).
Archiannelids were a major discovery in understanding evolution—these tiny worms living on the ocean floor are almost unchanged from 500 million years ago, making them living fossils that teach us what the earliest complex animals looked like.
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