The images presented here are examples of the morphological entity which has been named Stephanodiscus transilvanicus in all reports emminating from the Phytoplankton Laboratory of the Great Lakes Research Divison (now the Center for Great Lakes and Aquatic Sciences). All records developed for the United States Environmental Protection Agency, Great Lakes National Program Office from 1981-1988 and reported in Makarewicz (1987 and 1988) refer to the morphological entity pictured here.
Although this taxon is very distinctive there has been considerable taxonomic confusion associated with it. The multiseriate fascicles and the wide interfascicles should distinguish it from other taxa. There appears to be some morphological variability in the number of areolae at the margin which are reported by Stoermer and Yang (1969) to be 4-6. Areolae vary in placement and size giving a range of 14-20 in 10 micrometers. Fascicles and spines are 3-5 in 10 micrometers at the margin. Spines are robust usually with a spine near the margin of each interfascicle. The attachment of the spine is away from the margin. The valve is concentrically undulate with both concave and convex valves known.
Gaul et al. (1993) cite two SEM's of Stephanodiscus transilvanicus. The specimen illustrated in Thayer et al. (1983) is not conspecific with the specimens in Hakansson (1986) where Stephanodiscus transilvanicus has been typified. Presented here is a scanned image of the type designated by Hakansson in Diatom Research 1(1):29.
The image is used with the permission of BioPress, publisher of Diatom Research.
The true identity of the morphological entity we present is in need of additional taxonomic work.
Little can be said concerning the ecology of this taxon because of the taxonomic confusion asssociated with it. The work of Stoermer and Yang (1970) and Stoermer and Ladewski (1976) provide what little is known. It is abundant in the offshore waters of Lake Michigan in the present while historical collections showed it to be abundant in the nearshore areas also. It appears to have its greatest development in oligotrophic waters and tolerates some enrichment. Its apparent temperature preference is approximately 6 degrees Celcius. In Lake Ontario it is apparently absent from the modern flora but is a dominant in the sedimentary flora (Stoermer et al. 1985).