Article: A Silurian porpitoid hydrozoan from Cumbria, England, and a note on porpitoid relationships

A porpitoid hydrozoan, Pseudodiscophyllum windermerensis gen. et sp. nov., from Cumbria, represented by a well-preserved internal float (pneumatophore), is only the fourth porpitoid reported from Silurian rocks world-wide and the first to be found in any geological formation in England. Its circular pneumatophore is more than 110 mm in diameter. Because of the paucity of hard parts, these animals are not common as fossils but may have been important elements of the Palaeozoic oceanic plankton. Although the new species is superficially similar to the Ordovician Discophyllum, there are what appear to be fundamental differences. Similarities to species of Paropsonema, from the Devonian and Silurian, are also probably superficial. The wider relationships of these animals have long been misinterpreted in the palaeontological literature. They are not siphonophores. Correct understanding involves a complete re-interpretation of various homologies and of the evolutionary history of the group.