Neorhodella cyanea, a new genus in the Rhodellophyceae (Rhodophyta)

The red algal unicell Rhodella cyanea (Rhodellophyceae) was reinvestigated. The cell ultrastructure is clearly dissimilar to that of the two other Rhodella species, R. maculata Evans and R. violacea (Kornmann) Wehrmeyer. Consequently, we have established Neorhodella gen. nov. Neorhodella cyanea possesses a large parietal chloroplast with numerous lobes extending into the cell center. The inner region of each lobe terminates near the central nucleus and contains several thylakoids sparsely covered by opposed, disc-shaped phycobilisomes. These regions are interpreted as multiple pyrenoids. Thylakoids are more numerous in other chloroplast regions where phycobilisomes are alternately spaced. A peripheral encircling thylakoid is absent and plastoglobuli, in unicellular red algae found only in the Rhodellophyceae, are found at the cell periphery. Golgi bodies are exclusively perinuclear, similar to Dixoniella and Glaucosphaera in the class Rhodellophyceae. Golgi cisternae appear closely opposed during some cell cycle stages, a feature found in no other unicells except members of the Rhodellophyceae. Several stages of mitosis were observed in Neorhodella. These suggest a pattern fairly typical of other unicellular red algae. Nucleus-associated organelles are polar rings, the division poles have conspicuous gaps in the mostly intact nuclear envelope and microtubules emanate from a flattened plate of membranes and moderately electron dense material, attaching to small kinetochores during mitosis and terminating near the former poles of telophase nuclei during migration of daughter nuclei. The low molecular weight carbohydrate of Neorhodella is mannitol, similar to Rhodella and Dixoniella.