Pleurosira Guide
Credit: Pat Kociolek
  1. Valves orbicular
  2. Ocelli 2-4, prominent
  3. Rimoportula 1 or more, positioned near center of valve
  4. Valves form zig-zag colonies

Pleurosira has very large orbicular valves with 2-4 prominent ocelli, the number depending on salinity. The ocelli secrete mucopolysaccaride pads that join cells together in large, zig-zag colonies. One or more rimoportula are positioned near the center of the valve face. Colonies form filaments that are visible in streams.

Pleurosira is widely distributed in naturally saline waters and polluted waters. In older literature it was reported as a Biddulphia or Cerataulus.