Asterionella is a genus of pennate freshwater diatoms. Changes in pennation angle allow for variable gearing in pennate muscles. There are several different muscle architecture types including&colon; parallel, pennate and hydrostats. There is an important distinction seen between pennate muscles and other muscles. It is typically used to describe the contraction properties of pennate muscles. The third type of pennate subgroup is known as the multipennate architecture. The force produced by pennate muscles is greater than the force produced by parallel muscles. Nitzschia is a common pennate marine diatom. Diatoms are generally broken into two categories, the centric diatoms and the pennate diatoms. The lamina has indistinct longitudinal veins and numerous pennate veins. In a pennate muscle, PCSA is always larger than ACSA. Unlike pennate diatoms, centric diatoms never have a raphe. Conversely, in pennate diatoms both gametes lack flagella (isoogamous). This is more often observed in freshwater and pennate diatoms like "Pseudo-nitzschia". "Pseudo-nitzschia" species are bilaterally symmetrical Pennate diatoms.