Diploneis parma

THIS TAXON HAS NOT BEEN VERIFIED IN NORTH AMERICA.

Diploneis parma, however, is frequently misidentified or confused with other species of Diploneis.

The purpose of including a treatment of a taxon in Diatoms of North America that is not verified is to alert practitioners to the taxonomic and nomenclatural issues related to D. parma.

Diploneis parma was originally described by Cleve (1891). Publication of the lectotype of D. parma (Idei and Kokayasi 1986) and subsequent work, shows a long history of misidentifications in the diatom literature. Misidentifications continue to the present day, as shown more recently (Lange-Bertalot and Fuhrmann 2017). According to these two publications, D. parma has only been verified from Finland, Russia and Japan.

The original description of D. parma includes three localities (Rosslängen, Smaland, Sweden; Lake Lojo, Ab. 36, Finland; Lake Viando, Sb. 5 Finland). The slide from Lake Lojo (No. 12:36, Regio aboënsis, Lojo) was designated as the lectotype. Only two specimens were found on this slide, both are reproduced (above) from Idei and Kobayashi (1986).

Since the original publication, Diploneis parma has been reported by a number of workers in Europe (Hustedt 1937, Mölder and Tynni 1973, Krammer and Lange-Bertalot 1986, Hofmann et al. 2011) and North America (Stoermer 1978). All of these reports, however, illustrate specimens that do not conform to the type of D. parma.

Observations of D. parma, as based on lectotype specimens (Lange-Bertalot and Fuhrmann 2017):

L: 26-46
W: 17-27
S: 12-13 in 10 (15-16 in Finland, 12-14 in Russia)
A: 12-13 in 10

"Valves broadly elliptical, sometimes weakly rhombic-elliptical. Ends obtusely, more or less cuneately rounded. Length 26-46 µm, breadth 17-27 µm; length-to-breadth ratio ca. 1.3-1.7, i.e. rather low and with low variance in comparison to other taxa of the genus. Raphe filiform, curved and together with the internal flanking depressions gradually expanding to the central ends. Distal ends appear indistinct in LM. Central area ca. 3-4.5 µm wide, variable in shape from narrowly elliptic to moderately broad-elliptic, sometimes slightly constricted dependent on focus. Appendices (horns) are present as proximal raphe ends protrude into the central area. Canal system lanceolate, ca. 6-8 µm broad proximally, marked by two, rarely three canal raphe areolae set off from the striae areolae. Striae radiate throughout, 15-16 in 10 µm in specimens from Finland and Germany while 12-14 in 10 µm in specimens from Lake Ladoga (Russia) and from Japan. Arolae may appear at first uniseriate in LM but can be resolved as opposedly biseriate with appropriate focusing, 18-20 in 10 µm. This can be confirmed by SEM and TEM observations (see Idei & Kobayasi 1988, pl. 1-3). The areolae become alternating biseriate in the marginal parts."