Richard M. Crawford

THE GENUS ATTHEYA. I. A DESCRIPTION OF FOUR NEW TAXA, AND THE TRANSFER OF GONIOCEROS SEPTENTRIONALIS AND G. ARMATAS

Four new taxa belonging to the genus Attheya West are described from the west coast of Britain and from the North Sea. Attheya arenicola sp. nov. was found on sandy beaches in southwest Wales, Cornwall and the west coast of Scotland in the U.K., and on the edge of the North Sea at Renesse, Netherlands. A. flexuosa var. flexuosa sp. nov. and A. flexuosa var. enodulifer sp. nov. have been found in a similar habitat attached to cells of Hantzschia Grunow and Bacillaria Gmelin spp. A. longicorrus sp. nov. attaches to other diatoms in the plankton. Using light and electron microscopy, they are compared with A. decora West, the type species of Attheya, and with Chaetoceros sessilis Grontved, Gonioceros armatus (T. West) H. & M. Peragallo and Gonioceros septentrionalis (Ostrup) Round, Crawford & Mann. It is suggested that all taxa should be placed within Attheya because of similarity of horn structure and habitat preferences.

THE FRUSTULE STRUCTURE OF ORIGINAL MATERIAL OF AULACOSEIRA DISTANS (EHRENBERG) SIMONSEN

The original material from which Ehrenberg described Gallionella distans has been examined with light and electron microscopy with a view to understanding the morphology of a taxon that is now within the genus Aulacoseira and has a number of varieties. Aulacoseira distans has a distinctive heterovalvy, the “separation valves” that have no spines; areolae over the whole of the valve face; spines on the mantle edge are usually positioned between rows of areolae on the mantle which are in more or less straight rows; and a deep, thick ringleist with numerous rimoportulae against its inner side. Cells are found in short chains. This combination of characters does not match that in most published illustrations of A. distans and brings into question the taxonomic relationships of some of the published varieties. A lectotype has been chosen and deposted at BHU (the Ehrenberg collection at the Museum fur Naturkunde der Humboldt-Universitat in Berlin, and an isolectotype at BRM, (Bremerhaven).

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.

Morphology and Identity of Aulacoseira italica and typification of Aulacoseira (Bacillariophyta)

Original material of Ehrenbergs from Santa Fiora (Tuscany, Italy) was examined to establish the identity of the diatom to which Ehrenberg gave the name Gaillonella italica. It was compared with other Ehrenberg material, notably from New England, and with numerous other samples, both fossil and recent, with a view to understanding the taxonomy of this species. Although Ehrenberg later discarded the name, it was validly published and we consider it synonymous with G. crenulata. However, despite the earlier publication of G. italica, G. crenulata remains the type of the name of the genus Aulacoseira. New observations on the rimoportulae and the velum together with recent illustrations of separation valves have been added to the features used to distinguish the species from others in the genus, of which, the most important, though hitherto neglected, is the curving of the pore rows to the left (sinistrorse). We draw attention to the fact that A. italica has often been confused with A. valida.

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...

Ellerbeckia arenaria (Bacillariophyceae): formation of auxospores and initial cells

The development of auxospores and initial cells of the freshwater chain-forming diatom Ellerbeckia arenaria forma arenaria was studied using light and electron microscopy. Whether the auxospore mother cell is formed vegetatively (parthenogenesis) or through autogamy is still a matter for speculation. Because no signs of spermiogenesis could be detected in our material, we exclude oogamy. Further development involves retraction of the protoplast from the epivalve and the formation of a featureless siliceous cap with a central opening on its free surface. The homology and function of this cap remain uncertain. At the other end of the cell the protoplast remains tightly attached to the hypovalve throughout its further development. This hypovalve always has a concave valve face. An organic wall bearing many layers of overlapping, small silica scales begins to be formed while the cell is still enclosed within the mother cell wall, and allows the auxospore to swell, thus breaking the siliceous cap and girdle ba...

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.

Attheya ussurensis sp. nov. (Bacillariophyta)—a new marine diatom from the coastal waters of the Sea of Japan and a reappraisal of the genus

I.V. Stonik, T.Yu. Orlova and R.M. Crawford. 2006. Attheya ussurensis sp. nov. (Bacillariophyta)—a new marine diatom from the coastal waters of the Sea of Japan and a reappraisal of the genus. Phycologia 45: 141–147. DOI: 10.2216/04-48.1 A new species of the mainly sand-dwelling marine diatom genus Attheya is described from the Sea of Japan. Of the seven species of the genus, Attheya ussurensis most closely resembles Attheya decora in its valve and girdle structure and in its plastid form and number, but it also possesses features found in one or other of the remaining species (presence of a rimoportula, pores in the girdle bands and horn morphology). Keys are provided to aid ide.gification of all known Attheya species.

THE MORPHOLOGY AND TAXONOMY OF THE MARINE CENTRIC DIATOM GENUS PARALIA. II. PARALIA CRENULATA, P. FAUSTA AND THE NEW SPECIES, P. HENDEYI

Details of the morphology of three fossil species of the marine diatom genus Paralia are presented. Those of P. thybergii Stabell are added in order to distinguish it from P. crenulata (Grun.) Gleser which is illustrated from well-preserved material. Melosira fausta A Schmidt is newly combined with Paralia and illustrated for the first time with SEM; P. hendeyi Sims & Crawford is descibed as new. All are compared with each other, with the fossil species P. siberica (A. Schmidt) Crawford & Sims and with the only extant member of the genus, P. sulcata (Ehrenb.) Cleve.

Morphology of four plagiogrammacean diatoms; Dimeregramma minor var. nana, Neofragilaria nicobarica, Plagiogramma atomus and Psammogramma vigoensis gen. et sp. nov., and their phylogenetic relationship inferred from partial large subunit rDNA

A marine araphid pennate diatom obtained from sand grains sampled at two sites at Vigo, Spain is described as Psammogramma vigoensis S. Sato et Medlin, a member of the family Plagiogrammaceae, based on observations of frustule fine structure. The species possesses elongated valves with apical pore fields and parallel rows of striae oriented perpendicular to the apical axis. Valve poroids are occluded by perforated rotae. There is a weak sternum along the apical axis and rimoportulae are absent. Detailed observations of Dimeregramma minor var. nana (Gregory) Ralfs, Neofragilaria nicobarica Desikachary, Prasad et Prema and Plagiogramma atomus Greville, were also undertaken. Based on morphological features, the transfer of Neofragilaria nicobarica from the Fragilariaceae to the Plagiogrammaceae is proposed. Partial large subunit rDNA phylogeny also supported inclusion of both Psammogramma and Neofragilaria in Plagiogrammaceae.