Living disc-like hydrozoans such as the by-the-wind sailor and the blue button are often stranded in large numbers on beaches. These animals are delicate and rare as fossils as they require exceptional conditions for preservation. Here we describe a new example from the Bertie Group of upper New York State and Ontario (∼420 Ma), which is famous for the remarkably preserved sea scorpions (eurypterids) that occur there. The new hydrozoan, which gets up to 17 cm across and is the second-oldest example known, adds an important new member to this assemblage. It floated on the surface of the ocean and was occasionally incorporated into layers rich in eurypterids and other fossils.

Fossil capitate hydrozoans require exceptional conditions for preservation. Here we describe Bertratis ciurcae new genus, new species from the Silurian (Pridoli) of southern Ontario and upper New York State, where it occurs in association with a diverse assemblage of eurypterids. Only the float (pneumatophore) is well preserved, surviving as a thick carbonaceous compression. The new taxon is the largest fossil capitate reported, reaching a width of 17 cm, and the third Porpita-like example known from the Paleozoic. It was a rare pelagic component of the biota of the well-known Bertie Group Lagerstätten.