Taxonomy, ultrastructure and biogeography of the Actinella punctata species complex (Bacillariophyta: Eunotiaceae)

Members of the Actinella punctata species complex are investigated with light and scanning electron microscopy. A. punctata var. punctata is shown to range in length from 36 to 169 mu m. Spines outline the external valve margin, and the ventral margin has a protrusion or point that is elongate. A labiate process is present at both poles. A. punctata var. punctata is known from North America and Scandinavia only. A. australis comb. nov. and A. manguinii spec. nov. are species originally identified as subspecific taxa with A. punctata and known only from Madagascar. These two species are much smaller than the nominate variety of A. punctata and have a variable number and placement of labiate processes. Both A. australis and A. manguinii either lack labiate processes or have a single process per valve, which may be positioned at the headpole or footpole. Actinella punctata var. curta could not be confirmed from North America, and the original illustrations of this taxon, and specimens observed from Sierra Leone display an elongated protrusion or point on the dorsal margin of the valve. This feature suggests A. punctata var. curta may be more closely allied to African and South American Actinella species since they also have an elongate protrusion or point on the dorsal margin. Previous discussions about a broad biogeographic distribution of Actinella punctata do not seem to be supported, since the taxa previously assigned to this species complex do not appear to be closely related.