Modern Archaeomonadaceae from the land-fast ice off Adélie Land, East Antarctica: a preliminary report

Abstract

The land-fast ice and the platelet ice layer off Adélie Land are inhabited by a dense and diversified diatom community. Along with Bacillariophyceae, Archaeomonadaceae sensu Deflandre are present and relatively abundant. These modern siliceous nanostructures are similar to the nanofossils described by geologists in marine sediments from upper Cretaceous to Pliocene, Pleistocene and recently in Holocene and modern sediments, and are probably related to chrysophyte cysts. The two most abundant taxa were Achaeomonas cf areolata Deflandre and Litheusphaerella cf spectabilis Deflandre. The other taxa were not common. Despite the taxonomic uncertainty of immature forms, the diversity of archaeomonads was high. Three new species of Archaeomonas are described. The morphology of A. cf areolata is highly variable, showing a possible diversification over geologic time. Litheusphaerella cf spectabilis also shows some differences between fossil and modern specimens. Recent studies confirm that archaeomonads are extant in diverse marine water bodies and recent sediments. There is growing evidence that these siliceous structures represent possible reliable proxies of sea ice extent, even if their presence in geologic time is not always linked exclusively to sea ice. Further studies are needed to elucidate the exact origin of these cysts and their real taxonomic affinities.