The diatom genus Proboscia in Antarctic waters

Sundström (1986) erected the genus Proboscia for solenoid diatoms whose valves tapered to a proboscis, but only assigned one species to it, the boreal Rhizosolenia alata Brightwell. We have found three species in the modem Antarctic phytoplankton that are affiliated to Proboscia. One is apparently identical to Sundström's P. alata, whilst P. inermis (Castracane) Jordan & Ligowski comb. nov. and P. truncata (Karsten) Nöthig & Ligowski comb. nov. are easily distinguished on the basis of valve and proboscis morphology. Winter and spring forms seem to be present in all three species, the winter forms being characterised by longer probosces; heterovalvar cells are not unusual. Terminal auxospores are documented for all three species. Similar fossil taxa may also be assignable to Proboscia.