Friedel Hinz

Revision of the genus Navicula s.s. (Bacillariophyceae) in inland waters of the Sub-Antarctic and Antarctic with the description of five new species

Van de Vijver B., Zidarova R., Sterken M., Verleyen E., de Haan M., Vyverman W., Hinz F. and Sabbe K. 2011. Revision of the genus Navicula s.s. (Bacillariophyceae) in inland waters of the Sub-Antarctic and Antarctic with the description of five new species. Phycologia 50: 281–297. DOI: 10.2216/10-49.1 A revision of the diatom genus Navicula s.s. in inland water samples from the Sub-Antarctic and Antarctic resulted in the description of five new species, viz. Navicula australoshetlandica Van de Vijver sp. nov., N. dobrinatemniskovae Zidarova & Van de Vijver sp. nov., N. cremeri Van de Vijver & Zidarova sp. nov., N. conveyi Van de Vijver sp. nov. and Navicula bicephaloides Van de Vijver & Zidarova sp. nov. The new species are extensively compared with other similar species. The morphology and taxonomy of three other Navicula taxa present in the same materials are briefly discussed. A critical revision of literature reports of Navicula taxa in the Antarctic and Sub-Antarctic region indicates that despite the large number of records the genus is rather species-poor in the Sub-Antarctic and Antarctic. From a biogeographical point of view, there is a clear separation between the Sub-Antarctic localities in the southern Indian Ocean and the islands in the southern Atlantic Ocean, with several species showing a restricted biogeography.

Spatial and temporal distribution of assemblages of the diatom Corethron criophilum in the Polar Frontal region of the South Atlantic

Morphometric data in the form of frequency distributions of valve widths (transapical measurements) of the diatom Corethron criophilum have been plotted for stations between 50 and 47°S on transects 5, 11 and 12 of cruise ANT X/6 to the Atlantic sector of the Southern Ocean. The profiles largely confirm the picture of sharp differences between the waters as revealed by hydrological, pigment and other biological data. The assemblages to the north, which lie in the southern part of the Polar Frontal Zone water, are more congruent with those in water to the south, that is presumed to have eddied off the PFZ water, than with interlaying, Antarctic Circumpolar Current water. The profiles also show how assemblages of this species can be recognised over space and time. Furthermore, they reveal how a sexual event in the life cycle can lead to a rapid change in the character of the assemblage due to rapid loss of gametangial cell walls from the water column.

THREE SPECIES OF THE DIATOM GENUS CORETHRON CASTRACANE: STRUCTURE, DISTRIBUTION AND TAXONOMY

Three species of the marine planktonic diatom genus Corethron are recognized, and compared in detail using light and electron microscopy. The confusion in the use of some of the names given to taxa in the past is clarified, mainly based on differences in the morphology of the hooked spines. The commonly used combination, Corethron criophilum Castracane is discarded in favour of the earlier described entity, Actiniscus pennatus which was combined with Corethron in 1903 as Corethron pennatum (Grunow) Ostenfeld. The function of the tfiree types of spine found in the genus is discussed. It is proposed that the spines of the two species existing as single cells, C. pennatum and C. hystrix, serve to move apart and maintain separation of the cells in the ocean. Similar spines are found in C. inerme but there the cells are normally joined by linking spines to form long chains. The hooked spines have a similar role to play but we suggest that their main function is to secure the developing spine system in order to...

The spines of the centric diatom Corethron criophilum: Light microscopy of vegetative cell division

As part of a study of the biology of the marine planktonic centric diatom Corethron criophilum, cells have been followed through the vegetative cell cycle from immediately before cytokinesis until separation of the two daughter cells. After cytoplasmic cleavage, which lasts 30 min, each of the daughter cells becomes shorter and leaves space for the spines to develop on each of the new hypovalves. The relationship of the two cingula of each cell remains static for approximately 12 h while the new valves are developed. Expansion of both of the daughter cells in the pervalvar axis then withdraws the girdles from one another thus revealing the mature spines of the new hypovalves which now spring out to assume their final positions. The function of the cingulum in protecting and releasing the spines in this diatom is discussed.

An examination of species within the genus surirella from the malili lakes, sulawesi island, Indonesia, with descriptions of 11 new taxa

With 35 taxa reported by Hustedt (1942a), the genus Surirella (Turpin) is one of the most taxonomically rich and important genera in the Malili Lakes, a system of five ancient lakes located on the island of Sulawesi, Indonesia. We examine in detail the taxonomy of diatoms within the genus Surirella from the Malili Lakes. We also statistically evaluate valve morphology and relationships among taxa, and describe 11 new taxa. Results show Surirella taxa clustered according to unique combinations of morphological characteristics. Individuals within clusters often shared common valve shape, torsion, and presence of siliceous features including spines, spinules, and novel structures such as siliceous tendrils and tubular processes along the median area. We demonstrate that the siliceous tendrils of Surirella sublinearis and its varieties, and S. tenacis are used for attachment to substrata and further postulate that the evolutionary development of attachment features contributes to the substantial diversity of Surirella taxa in this ancient lake system.

The combination of Chaetoceros gaussii (Bacillariophyta) with Attheya

Abstract The extremely rare, single-celled diatom Chaeloceros gausii is reported from a polynya in the southern Weddell Sea. Comparison of this material with preparations made by Heiden from the German South Pole expedition of 1901–1903 and with cultured cells has revealed affinities with the genus Attheya of benthic habitats and the combination Attheya gaussii (Heiden in Heiden & Kolbe) Crawford is proposed. Although found in the open water, we suspect that the diatom grows attached to sea ice in a similar situation to that shown by Attheya septentrionalis, which is its larger counterpart in the Arctic. An epitype is selected to support the lectotype illustrated by Simonsen in 1992.

Fragilariforma javanica comb. nov.: analysis of type material of a widely reported species with a tropical distribution

The transfer of Fragilaria javanica Hustedt to the genus Fragilariforma D.M. Williams & Round is presented based on a detailed analysis of the type material from Java (Malay Archipelago) using light and scanning electron microscopy. The taxon is characterized by each areola covered externally with a rota, well-developed, simple apical pore fields composed of rounded poroids and located on both valve apices, denticulate spines with tips oriented towards the apices, and open girdle bands with valvocopulae bearing heavily silicified advalvar fimbriae. These features are all shared with species currently ascribed to Fragilariforma, although the spine shape and orientation, and girdle elements having two rows of areolae, along with valvocopulae with well-developed fimbriae are typical of F. javanica. Morphological, ecological and distribution data are presented and discussed based on available literature for this taxon.

Observations on the diatom Navicula hedinii Hustedt (Bacillariophyceae) and its transfer to a new genus Envekadea Van de Vijver et al. gen. nov.

The population of an unknown naviculoid diatom from Lake Vrana in Croatia was identified as Navicula hedinii, a species described in 1922 from a small lake in eastern Turkestan (China). This species has some similarities with Navicula pseudocrassirostris, a marine species found in European coastal waters. Based on the ultrastructure of the two species, they can no longer be included within the taxonomical concept of Navicula sensu stricto. Following a comparative morphological analysis of both species with genera bearing similar characters (Adlafia, Veigaludwigia, Kobayasiella, Cavinula, Stenoneis, Climaconeis, Berkeleya, Sellaphora, Cosmioneis), a new genus, Envekadea is proposed for the two species. The new genus is characterized by a sigmoid raphe course with golfclub-like terminal fissures deflected in opposite directions, the areolae covered by external porous hymenes and the presence of one chloroplast, H-shaped in valve view.

Studies on Amphora subgenus Halamphora (Bacillariophyta): the revision of some species described by Hustedt using type material

As part of an analysis of type material of Amphora species described by Hustedt, the lectotypes of Amphora fontinalis, A. rugosa and A. schroederi and the holotype of A. subturgida were analysed. Light microscopy showed that all these tropical freshwater taxa are similar in frustule and valve outline, position of the raphe, appearance of the dorsal striae and thickening of the central dorsal virgae. Scanning electron microscopy allowed reliable differentiation between the four, based on the morphology of dorsal striae, dorsal areolae, conopeum, proximal raphe fissures, presence or absence of an inner longitudinal rib close to the raphe sternum, and degree of thickening of the central dorsal virgae. Previous reports of A. fontinalis from Tahiti and Moorea were confirmed while reports of this species from Australia and of A. subturgida from Mauritius, Papua and Israel were refuted. Based on our results, species descriptions are emended and the distributions of these four species are revised. Comparisons of these species and others of the subgenus Halamphora are presented.

AN EMENDED DESCRIPTION OF AMPHORA TUMIDA HUSTEDT (BACILLARIOPHYCEAE)

Material chosen as the lectotype of Amphora tumida Hustedt by Simonsen was examined with light and scanning electron microscopy. Based on this analysis a more comprehensive concept of this taxon was established and the description emended. A comparison with the morphologically similar A. subacutiuscula Schoeman and A. acutiuscula Kützing sensu Archibald strongly suggests that A. tumida is present in South African waters, in addition to its confirmed records from Venezuela and Argentina.