Study of three upper Ordovician borehole sections from Estonia has revealed abundant and well-preserved scolecodonts representing more than 50 species of jaw-bearing eunicid polychaetes. In this paper, two monotypic families, Conjungaspidae and Tretoprionidae, are introduced, based on two new species (Conjungaspis minutus gen. et sp. nov. and Tretoprion astae gen. et sp. nov.). The most distinctive features of conjungaspids are the small, distally rounded and long-horned carriers, merged with large basal and laeobasal plates, and symmetrical jaw apparatus. Conjungaspids are supposedly a primitive group displaying common features with some placognaths and labidognaths. Tretoprionids are characterized by sub-transversely prolonged and strongly elevated scraper-like denticles in the anterior part of the posterior maxillae, unusual anterior maxillae composed of several weakly fused teeth, and occurrence of a hole or large incision in the outer face of the left posterior maxilla.