Lectotypification of Paralia sulcata and description of P. obscura sp. nov. (Bacillariophyta) from the Ehrenberg Collection

Abstract

Sediment samples originally collected in Oran, Algeria and later dated to the Miocene from the Ehrenberg Collection were examined for specimens of Paralia sulcata(Ehrenberg) Cleve. Two morphologically distinct entities fitting the currently widely used definition of the species were found. In this material, they were easily segregated by the morphology of fenestrae and several other, more subtle characters. Consistent with Ehrenberg's illustrations, the valves with ‘open fenestrae’ and a 1:1 ratio of fenestrae to marginal linking spines were designated as P. sulcata and a mica slide preparation from the Ehrenberg Collection was designated as a lectotype for the species. An emended circumscription of P. sulcata using specimens examined under electron microscopy was presented. Other striking morphological characters in P. sulcata valves included the rimoportula internal opening underneath the lip of the mantle edge, the marked external aperture of rimoportulae and the slits of the cingulum located at the edge of each band. Valves with ‘obscured fenestrae’ and a 2:1 ratio of fenestrae to marginal linking spines are designated here as P. obscura MacGillivary sp. nov.. The morphology of P. sulcata presented here is compared with those of contemporary and fossil specimens attributed to P. sulcata sensu lato and a few other, similar, previously described Paralia species, most importantly the contemporary species with open fenestrae, P. fenestrata Sawai & Nagumo. It is hoped this will facilitate a clearer understanding of Ehrenberg's concept of P. sulcata for future taxonomic studies of this genus.