Two multi-stigmate Gomphonetna species of Africa: Gomphonema kalahariense (nom. nov., stat. nov.) and Gomphonema chemeron (sp. nov.)

摘要

The taxonomy and morphology of two taxa of the diatom genus Gomphonema with multiple stigmata from fossil localities in Africa are considered. Light and scanning electron microscopy as well as quantitative analysis of valve shape suggest two taxa are present in these collections. One of them, previously described as Gomphonema ventricosum var. africana, has 2-4 stigmata and conforms well with the original illustration of this taxon by Reichelt. However, this taxon does not appear to be closely related to G. ventricosum, and is a species in its own right, so a new name, G. kalahariense nom. nov., stat. nov. Jeff.R.Stone & Kociolek is proposed. This species is known from modern and fossil locations in Africa. A second species, Gomphonema chemeron Jeff.R.Stone, Westover & Kociolek sp. nov. is described from diatomite deposits of the Baringo Basin, Kenya, that are approximately 2.6 million years of age. This species, with 3-7 stigmata, has a distinctive shape and is easily distinguished from G. kalahariense. We compare these species with other multi-stigmate members of Gomphonema, including G. krammeri Reichardt, a fossil species described from Mexico and Cuba.