<i>CYCLOTUBICOALITUS UNDATUS</i>, GENUS ET SPECIES NOVA

A new genus and species of the family Thalassiosiraceae, Cyclotubicoalitus undatus, is described. It is distinguished from other known taxa by the presence of compound external processes, each composed of an occluded process and the external part of a fultoportula, fused into a single structure. A single rimoportula is present; central processes are lacking. Ribs are absent internally and externally. The areolae have domed internal cribra. The only known population comes from an eutrophic, warm water habitat in southeastern North America.