Marine Apartectal (Chamberless) Mastogloiaceae (Diatomeae: Bacillariales): Paramastogloia cubana gen. nov., sp. nov., New Observations and Emended Diagnosis of Mastoneis, and Comparison with Mastogloiopsis

Mastogloia is a large, morphologically diverse genus of primarily benthic marine species defined by the presence of partecta (chambers) on the valvocopula (girdle band next to the valve). Several genera have been found with valves that resemble Mastogloia but lack the ring of partecta; the most diverse group is in freshwaters, especially Aneumastus, but there are two marine genera, both monotypic. A third such species has been found in Cuba and is described here as Paramastogloia cubana gen. nov., sp. nov. Paramastogloia cubana, Mastoneis biformis, and Mastogloiopsis biseriata each resemble the valve structure of some species of Mastogloia but do not resemble one another. Paramastogloia is indistinguishable in light microscopy (LM) from naviculoid diatoms and had been identified as Navicula cf. sovereigniae. The resemblance of P. cubana to Mastogloia is in the areolae, particularly to those of M. umbra, M. dicephala, and M. mammosa, three species not likely to be in one monophyletic group. Mastoneis has been observed in LM from widespread warm-water localities and resembles some Mastogloia in having costae extending partway across the virgae (interstriae); new ultrastructural details are presented showing the girdle bands and absence of partecta, and a clearer genus diagnosis is proposed. The third genus, Mastogloiopsis, was established with ultrastructure and resembles species of Mastogloia sec. Marginulatae. The range of areolar characters that might be admissible to Paramastogloia is unknown, so the generic diagnosis has been left imprecise to allow for the possibility of other species. The relationships among these genera await genetic studies, which are still scarce in Mastogloiaceae.