Mereschkowsky 1903 Category: Symmetrical biraphid
TYPE SPECIES: Placoneis gastrum (Ehrenberg) Mereschkowsky
Smallest to largest - 4 taxa sorted by maximum length
The valve outline of Placoneis is linear to lanceolate, sometimes with rostrate or capitate ends. The areolae are loculate and internally occluded. Areolae form uniseriate striae. The axial area is narrow. The proximal raphe ends are straight and slightly expanded externally. The plastid is large, distinct, and divided into two X-shaped plates.
Placoneis contains a number of species that grow in epipelic habitats of lakes and streams. It includes the former Placoneis exigua (Gregory) Mereschkowsky and its allies. The taxonomic position of the genus is unclear, as it has been suggested to hold naviculoid as well as cymbelloid and gomphonemoid affinities (Mann and Stickle 1995, Kociolek and Thomas 2010).
Cite This Page:
Spaulding, S., Edlund, M., and Metzeltin, D. (2008). Placoneis. In Diatoms of the United States. Retrieved May 30, 2016, from http://westerndiatoms.colorado.edu/taxa/genus/Placoneis
The generitype had been posted as Placoneis exigua (Gregory) Mereschkowsky on this website. It was corrected to Placoneis gastrum (Ehrenberg) Mereschkovsky based on Cox (2003) and Jahn (2004) as of May 1, 2011. - S. Spaulding