Livingstonia (Thalassiosirales, Bacillariophyta), a new genus of fultoportulate centric diatoms from an Atlantic coastal plain river in Florida, southeastern United States

Abstract

Prasad A.K.S.K and Nienow J.A. 2011. Livingstonia (Thalassiosirales, Bacillariophyta), a new genus of fultoportulate centric diatoms from an Atlantic coastal plain river in Florida, southeastern United States. Phycologia 50: 264–280. DOI: 10.2216/09-89.1A morphological and taxonomic account of Livingstonia palatkaensis, a new genus and species of centric diatoms belonging to the order Thalassiosirales Glezer & Makarova, is provided. Descriptions are based on material collected from the St. Johns River, a major, highly colored blackwater river in the Atlantic coastal plain in the southeastern United States. Scanning electron microscopic observations clearly show that although the valve structure in Livingstonia shares broad similarities with the genera Thalassiosira and Skeletonema, the types of the two fultoportulate families Thalassiosiraceae and Skeletonemataceae, respectively, it is sufficiently dissimilar to warrant the description of a new genus. Livingstonia is characterized by the presence of compound marginal processes, each formed from the external extension of a fultoportula and a semielliptical hyaline hood or cover. The areolae have semicontinuous internal cribra. A single rimoportula is present near the valve center. No fultoportulae are found at or near the center of the valve face. Furthermore, Livingstonia lacks connecting threads of marginal fultoportulae and an external extension of the rimoportula on the valve face, a combination of features that is unusual in the genus Skeletonema. Livingstonia is also distinguished from two recently described freshwater genera in the Thalassiosiraceae from the southeastern United States, Cyclotubicoalitus and Spicaticribra, in having a rimoportula away from the margin but close to the center of the valve and in other key characteristics. A note on another freshwater, co-occurring, more frequent and widespread, chain-forming, closely related diatom, Skeletonema potamas, is also included. Livingstonia is tentatively placed in the family Thalassiosiraceae.