Fallacia2 Guide
Credit: Pat Kociolek
  1. Valves linear-lanceolate to elliptic
  2. Hyaline area on valve face, characteristically lyre-shaped

Valves of Fallacia are linear-lanceolate to elliptic, with bluntly rounded ends. A thin siliceous covering, or canopeum, covers the striae on the external valve surface. A lyre-shaped non-ornamented area is present on the valve surface. The canopeum can not be resolved in the light microscope, but slits, or linear openings of the canopeum, may be visible at the valve apices. In living cells, the canopeum may be filled with cyanobacteria that fix atmospheric nitrogen. The chloroplasts are H-shaped and consist of two plates that lie against the girdle. The two plates of the plastid are connected by a narrow isthmus that lies against the epivalve.

Fallacia includes the former Navicula pygmaea Kützing and its allies. Many species are found in marine tropical waters, but a few species occur in North American in epipelic habitats of high conductance. The genus Pseudofallacia was established (Lui et al. 2012), resulting in a more narrow circumscription to Fallacia.