Entwisleia bella, gen. et sp. nov., a novel marine ‘batrachospermaceous’ red alga from southeastern Tasmania representing a new family and order in the Nemaliophycidae

Abstract

A new family, genus and species in the new order Entwisleiales of the subclass Nemaliophycidae are described for a subtidal marine red alga (Entwisleia bella F.J. Scott, G.W. Saunders & Kraft) from Tasmania in Australia’s cool-temperate southeast. Thalli are uniaxial, the stout cells of the single central-axial filament bearing varying numbers of whorled periaxial cells and fascicles of determinant cortical filaments at their distal poles, as well as dense aggregates of secondary internodal filaments arising perpendicularly on basipetal rhizoids that issue from periaxial cells. Plants are dioecious, the spermatangia sessile on distal bearing cells of primary and secondary cortical filaments. Carpogonial branches are four- to eight-celled and directed outwardly from the thallus, and produce simple to highly branched laterals from subhypogynous cells. Presumed fertilization results in several gonimoblast initials being cut from the lateral surface of the carpogonium by vertical cross walls, the ensuing gonimoblasts forming a compact carposporophyte subtended by, but not mixed with, the sterile filaments on the carpogonial branch. Terminal carposporangia form across the surface layer of the gonimoblasts and a fusion cell is not produced. The thalli are particularly batrachospermaceous in vegetative and reproductive morphology, a highly anomalous phenomenon considering that the Batrachospermales is an order totally confined to freshwater habitats. Despite the morphological and anatomical similarities to Batrachospermum and closely related genera, the consensus of multigene sequence analyses indicates that the new genus forms a sister clade to the Colaconematales, even though the members of that group differ in virtually every aspect of habit and anatomy from the gametophytic thalli of Entwisleia.