Anomoeoneis sculpta

Valves are broadly elliptic, with apiculate apices. The axial area is narrow and bordered on each side by an isolated column of areolae. The central area is large, symmetric and shaped like a lyre. The central area is covered with surficial spots of various shapes and sizes. The central area does not reach to the valve margin. The central nodule is transversely elliptic and largely void of spots. Raphe branches are lateral, becoming filiform near the terminal fissures, which are deflected to one side. Proximal raphe ends are bent gently to the same side and terminate in large, bulbous pores. Striae are weakly radiate at the valve center, becoming more radiate near the apices, then parallel at the apices. Lateral spacing of areolae is variable except near the valve margins, where the areolae number 9-13 in 10 µm.

Two distinct morphotypes have been reported as Anomoeoneis sculpta in North America. The one described here is the most common and widespread of the two. The other one is pictured, without description, in the Autecology section below. Both of these taxa differ from the type of this taxon in valve shape, end shape and/or shape of the central area. Therefore, future work may find that these morphotypes are deserving of description as distinct taxa. Other specimens that have been recorded from Europe (see Krammer and Lange-Bertalot 1986 and Schmidt 1874-1959) also have different morphologies compared to North American specimens. The specimen that Patrick and Reimer (1966) used to illustrate this taxon was collected in Bohemia and apparently lacks spots in the central area (Plate 32, Fig. 2).

This taxon has also been reported as a form and as a variety of Anomoeoneis sphaerophora. Based on culture experiments, Schmid (1979) claimed that both A. sphaerophora f. sculpta and A. sphaerophora f. costata are intermediate morphological stages in the life cycle of A. sphaerophora. However, photographic evidence of these transition stages is lacking and until these life cycle intermediates can be repeated, we elect to display A. sculpta at the species rank.