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A steinkern of an endoceratid nautiloid siphuncle contains a Trypanites sozialis boring with a lingulate brachiopod Rowellella sp. shell inside. The steinkern of this endoceratid formed during early lithification of the sediment on the seafloor. The lithified steinkern of this siphuncle was either initially partially exposed to the seawater or was exhumed and stayed exposed on the seafloor, where it was colonized by boring organisms. This bioerosion resulted in numerous Trypanites borings in the siphuncle. After the death or exit of the Trypanites trace maker, a vacant boring was colonized by a small lingulate nestler Rowellella sp. This lingulate was likely preadapted to life in hard substrate borings when it first found its way into borings in living substrates in the Late Ordovician. The increased availability of hard substrate borings, combined with the increased predation pressure due to the GOBE, enhanced the colonization of hard substrate borings by lingulate brachiopods.

A new sinistrally coiled univalved mollusk Catalanispira n. gen. is described with two species; Catalanispira reinwaldti (Öpik, 1930) from the Middle Ordovician Kõgekallas Formation (Darriwilian) of Estonia and Catalanispira plattevillensis n. gen. n. sp. from the Upper Ordovician Platteville Formation (Sandbian) of northern Illinois, USA. Morphological features include a large, low-trochiform shell, a narrow lenticular aperture, a deep funnel-like umbilicus, a falcate inner lip and a large (1.4 mm wide) protoconch. Ornamentation consists of fine commarginal growth lines or ribs but superimposed on a slightly irregular shell surface. Catalanispira n. gen. is placed within the sinistrally coiled order Mimospirida and the family Onychochilidae, and Catalanispirinae n. subfam. is proposed. The large Lower Ordovician (Tremadocian) Pelecyogyra Ebbestad and Lefebvre, 2015 from Morocco and France is transferred to this new subfamily. The well-preserved initial growth stage of Catalanispira plattevillensis n. gen. n. sp. is cap-shaped, slightly asymmetrical, unusually large, and smooth, and represents either an unusually large embryonic shell (protoconch 1) or a larval shell (protoconch 2). It differs from the smaller protoconch described for the clisospirine Mimospira Koken in Koken and Perner, 1925, which might include a multiwhorled larval shell (protoconch 2). Mimospirids are dominantly Ordovician, and have been classified as untorted mollusks (only distantly related to gastropods), dextral hyperstrophic gastropods, or sinistral orthostrophic gastropods. Sinistral asymmetry already in the embryonic shell and lack of conclusive evidence for coiling direction, e.g., an operculum, could suggest that Catalanispira n. gen. or similar mimosprids were sinistral orthostrophic gastropods. Currently the group is therefore classified as a group of sinistral orthostrophic gastropods, unranked within the Gastropoda.

Rare Oichnus simplex drill holes occur in mature obolid shells from the Cambrian/Ordovician boundary beds of northern Estonia (Iru and Ãœlgase) and the uppermost Cambrian of NW Russia (Lava River). The drill holes are significantly more common in the central rather than the marginal regions of the obolid valves. Drilling predators attacked Ungula ingrica in the Kallavere Formation and Ungula convexa in the Ladoga Formation. Failed predatory attacks on obolids were relatively common in the latest Cambrian-earliest Tremadocian of Estonia. Presumably drilling predators at Lava River and Iru differed from those at the Ãœlgase as indicated by significant differences in drill hole sizes at these locations. Most likely some types of worms preyed on obolids in the latest Cambrian-earliest Tremadocian of Estonia and latest Cambrian of NW Russia. The predation rate (6% to 9%) of studied obolids indicates that they likely had an epibenthic life mode. In addition to Oichnus drill holes in the obolids, there are also common pseudoborings caused by mineral dissolution.

The biogeographical distribution of Ordovician and Silurian gastropods, monoplacophorans and mimospirids has beenanalysed on a generic level. The dataset contains 334 genera and 2769 species, yielding 1231 records of genera with 2274 occurrencesworldwide. There is a bias towards eastern Laurentia, Baltica and Perunica records. Some 53.1% of the records are Ordovician. The study demonstrates that these molluscs are well suited to being used to improve understanding of Ordovician and Silurian biogeographicalprovinciality. Specific points are that: a Lower Ordovician assemblage is evident in Laurentia; the fauna of the Argentinean Precordillera is Laurentian until the Darriwilian, when taxa are shared with North China; Late Silurian gastropods from the Alexander terrane (SE Alaska) are unknown in Laurentia, but support a rift origin of this terrane from NE Siberia; Perunica, Ibero-Armorica and Morocco cluster together throughout the Ordovician but Perunica and Morocco are closer; Darriwilian–Sandbian deep-water Bohemian taxaoccur in Baltica; a Laurentian–Baltica proximity is unsupported until the Silurian; Siberia clusters with North China and eastern Laurentia during the Tremadocian–Darriwilian; during the Gorstian–Pridoli Siberia clusters with the Farewell and Alexander terranes; North China may have been close to Laurentia and the Argentinean margin of Gondwana; and the affinity of Tarim taxa is problematic.

Redescription of the gastropod Euomphalus undiferus Schmidt, 1858 from dir Upper Llandovery Rumba Formation of Estonia requires reinvestigation of the hitherto monotypic genus Kiaeromphalus Peel & Yochelson, 1976, originally described from the Rytteraker, Addresses: Isakar M, Tartu State Univ, Museum Geol, Vanemuise 46, EE-51014 Tartu, Estonia. Tartu State Univ, Museum Geol, EE-51014 Tartu, Estonia. Uppsala Univ, Dept Earth Sci Histor Geol & Palaeontol, S-75236 Uppsala, Sweden.