The problematic lingulate brachiopod Aulonotreta from the Ordovician (Dapingian–Darriwilian) of Baltoscandia

The enigmatic and aberrant lingulate brachiopod Aulonotreta antiquissima (Eichwald) from the Dapingian (Volkhov Stage) Toila Formation of northern Estonia and St Petersburg area (Historical Region of Ingria, Ingermanland, or Inkerinmaa; English, Swedish, Finnish) is re-described together with the new species, Aulonotreta neptuni, from the lower Darriwilian (Kunda Stage, lower Valastean Substage) Holen Limestone on the Island of Öland, southern Sweden. The genus is presently endemic to Baltoscandia. The new well-preserved material of Aulonotreta permits an account of the musculature, micro-ornamentation and siphonotretoid-like and non-baculate shell structure, all of which were previously poorly understood. The aberrant morphology and musculature of Aulonotreta suggest that it was adapted to an entirely epifaunal and most likely ambitopic adult mode of life.