One species of Microtabella, Microtabella interrupta, is widespread and has been known since the 19th Century but it has a convoluted taxonomic history leaving it presently the only species in the genus. The name interrupta derives from the chain-forming habit and the plastids being confined to a portion of the cell by a set of distinctively distended septa. This character makes it very easy to identify and very easy to overlook similar species, especially because the tabulate frustules are most often seen in girdle view. I found specimens of a new taxon that had these characters and was distinguished with difficulty in girdle view by the coarser striae on the copulae and the recurved edges of the septa. However, in valve view Microtabella rhombica n. sp. has a much broader, rhombic outline. Ultrastructural differences include a more elongated apical pore field with a prominent spine, biseriate striae on the copulae and a different form of the ligule (a raised bar on the last copula). Like Microtabella interrupta, the mature epitheca of Microtabella rhombica comprises numerous copulae with nearly flat septa, two copulae with distended septa and four hyaline pleurae that lack septa. This species could well be widespread but, as with other monospecific genera in which there is a strong distinguishing character, care must be taken to look beyond the outstanding feature.

Lucanicum concatenatum is a chain-forming araphid pennate, assigned to Cyclophorales: Cyclophoraceae on the basis of morphological characters and DNA sequences, resembling Neosynedra, but with platelike plastids and striae mostly undivided by vimines. So far it has only been found growing on blue coral, Heliopora coerulea, but we do not suggest that it is restricted to this habitat. Its phylogenetic position, near Cyclophora, Florella and Astrosyne, requires amendment of the diagnosis of Cyclophorales, which included characters unique to C. tenuis, the only species in the order at that time. The question of the scope and description of the Cyclophoraceae remains unresolved.