CYMBELLONITZSCHIA DILUVIANA HUSTEDT (BACILLARIOPHYCEAE) - HABITAT ANDAUXOSPORULATION

The diatom Cymbellonitzschia diluviana Hustedt is an important indicat or species in interglacial deposits but is rarely reported from contem porary sites. The presence of large populations in Lough Neagh, N. Ire land, made possible a study of its ecology and auxosporulation. The ap ical length of cells in the lake was usually between 7 and 25 mu m, bu t in culture there was a broader range between 5 and 42 mu m. Amongst smaller cells (< 11 mu m), some (3 %) were found with raphes on the 'd orsal' (i.e. convex side) rather than usual 'ventral' side. At cell di vision. both daughter cells had 'hantzschioid' symmetry. C. diluviana is found in alkaline waters (pH 7.6-9.0) but not usually where there i s significant calcite deposition. Its present rarity is probably becau se its preferred habitat is now less common. In L. Neagh, C. diluviana was found on exposed rocky and sandy shores, but was particularly abu ndant in shifting sand bars. This highly abrasive and erosive environm ent requires cells to have good adhesion and the ability to withstand extended periods of burial. C. diluviana is essentially a ruderal spec ies, adapted to habitats with high disturbance.