Bacillaria Guide
Credit: Ian Bishop and Pat Kociolek
  1. Raphe positioned in the central apical axis
  2. Striae relatively coarse
  3. Cells grow in colonies, linked by their keels

The raphe of Bacillaria species is located within a raised keel. In contrast to the excentrically positioned raphe and keel of Nitzschia, the raphe of Bacillaria is centrally positioned along the apical axis. The striae are distinct and relatively coarse. Living cells form colonies. The colonies are joined by silica hooks near the keel, and these silica hooks allow the cells to slide past one another in coordinated movements.

Bacillaria is found in marine, brackish, and freshwaters with high conductivity and often nutrient rich conditions. Planktonic colonies of Bacillaria have a unique and characteristic movement.

In fact, this diatom is the first diatom observed - as Vibrio paxillifer by Müller (1786). Müller observed, and illustrated colonies of this diatom in its variety of cell arrangement. In a fascinating twist, this diatom was first placed in the genus Vibrio, which is the genus that includes the cholera bacteria, V. cholerae. Shortly after its initial description, Gemlin (1788) considered Bacillaria to be sufficiently distinctive to place it in its own genus. With the designation of Bacillaria, the first genus of diatoms was formally described. The name Bacillaria thus became the name of the class to which all other diatoms now belong. Furthermore, in taxonomic literature, diatoms are referred to as Bacillariophyceae or Bacillariophyta.

The genus Bacillaria was revised (Jahn and Schmid 2007), with recognition of additional species. Bacillaria paxillifera var. czarneckii was described from material from the Mississippi, but also documented in Europe. Bacillaria kuseliae and B. urve-millerae were described from Germany and Australia, respectively. These taxa differ in the structure of the raphe flanges, valve shape and plastid shape and number. It is likely that these species and varieties are not being recognized by most surveys.