A review of the cyclostomiceratid nautiloids, including new taxa from the Lower Ordovician of Öland, Sweden

Cyclostomiceratidae is a distinct family of early Ordovician, small, gomphoceroid to breviconic ellesmerocerid nautiloids which possess an adorally contracting aperture. The family ranges in age from Arenig to early Llanvirn and is recorded from the USA, northern Argentina, east China and Baltoscandia. This paper reviews the family's status, origin, stratigraphical occurrence and systematics. Three new taxa are described from the lower Kundan Stage of northern Öland, Sweden: Pictetoceras oliviae sp. nov., Parcydostomiceras pautitumidum sp. nov. and Microstomiceras holmi gen. et sp. nov. These cyclostomiceratids are extremely well preserved and extend our knowledge of the morphology, biostratigraphy and palaeogeographical distribution of the family. Microstomiceras gen. nov. is one of the smallest nautiloids described from the Lower Palaeozoic.