What is "haplodrili"

Haplodrili, or Archiannelida, is an order of primitive polychaete worms. Zoologist Ray Lankester gave it the name haplodrili, while zoologist Berthold Hatschek later named it Archiannelida. Once considered to be a class under Annelida, and even a separate phylum, haplodrili is now widely accepted to be an order under Polychaeta. Species in this order are known for completely lacking external segments.