Shionodiscus caspicus sp. nov. (Bacillariophyta, Thalassiosiraceae) from the Caspian Sea and four nomenclatural combinations for Shionodiscus

Abstract

The article focuses on a description of a new species, Shionodiscus caspicus Gogorev et Kovaleva, sp. nov., also providing LM and SEM photomicrographs. Based on (sub)central fultoportulae number, the authors distinguish three morphotypes of the species. A comparison with morphologically similar taxa is provided. The new species is similar to S. frenguellii, S. latimarginatus, S. oestrupii, and S. trifultus, but differs in the number of central fultoportulae, as well as the density of marginal fultoportulae and location of rimoportula. The taxonomic features of the genus Shionodiscus are discussed and one of the features — the length of fultoportula — is elaborated and specified in the generic diagnosis. Based on a series of morphological features, such as reduced or absent external tubes of strutted processes and location of rimoportula, the four combinations are proposed: Shionodiscus diporocyclus (Hasle) Gogorev, comb. nov., Shionodiscus ignotus (I. V. Makarova) Gogorev, comb. nov., Shionodiscus maculatus (G. A. Fryxell et J. R. Johans.) Gogorev, comb. nov., Shionodiscus subtilis (Ostenf.) Gogorev, comb. nov.