Simulacra in the diatom genus Diploneis (Diatomeae: Naviculales): Caribbean Diploneis gravelleana and other small, strongly constricted species resolved from ultrastructure

Diploneis gravelleana Hagelstein was described in 1939 from Puerto Rico but may later have been confused with Diploneis interrupta var. caffra Giffen, described in 1960 from South Africa. Both are small (ca 20 μm in length), strongly constricted species indistinguishable in light microscopy. When we found a similar species in Micronesia, we needed to determine if it matched either of these species. We obtained mud samples from the US Virgin Islands containing D. gravelleana and unmounted type material of Giffen's original material for SEM imaging. All three populations differed ultrastructurally and hence the Micronesian species is described as Diploneis carolinensis sp. nov. Lobban et Witkowski. Diploneis carolinensis was found in mangrove samples from Yap and Palau. These simulacra suggest that D. caffra may not be as widely distributed as supposed.