Chaetoceros muelleri

Cells form filamentous colonies, with neighboring valves linked by twisted setae that extend from the pole of each valve. Valves and setae are lightly silicified. Valves are elliptic. Dissociated frustules result in neighboring valves remaining connected valve face to valve face. The valve face of the intercalary cells are slightly convex. The terminal frustules of colonies have concave valve faces. The valve face lacks distinct ornamentation. A central process, however, (a rimoportula?) may aid in filament formation. The setae of the terminal valve are bent strongly away from the colony.

Internally formed resting spores (endogenous spores) are heavily silicified. Resting spores have a convex primary valve, and secondary valve with a prominent raised annulus.

Typical diatom sample preparation, such as hydrogen peroxide and nitric acid treatments, often dissolves the organic material that supports the lightly silicified valves and filaments.

The taxonomy of North American Chaeotoceros, particularly C. mueller and C. elmorei, has received attention (Johansen and Rushforth 1985, Rushforth and Johansen 1986, Johansen and Boyer 1995). Rushforth. Here we follow the conclusions reached by Johansen et al. (1990) who proposed synonymy of C. muelleri and C. elmorei based on culture studies. In culture, C. muelleri (single cells) and C. elmorei (chains) formed from the same clones. Chaetoceros muelleri is the older valid name, and has nomenclatural priority.