Final answer:
Diatoms are unicellular photosynthetic protists with silica shells known as frustules and are part of the stramenopiles group. They play a key role in aquatic ecosystems as a major component of plankton. Stramenopiles, including diatoms, golden algae, and brown algae, have unique flagella and diverse morphologies.
Step-by-step explanation:
The algae in question with a silica shell that is split into two frustules are known as diatoms, a group within the stramenopiles, which also includes organisms like brown algae, golden algae, and Oomycetes. Diatoms are unicellular photosynthetic protists that create intricately patterned glassy cell walls composed of silicon dioxide. These organisms are significant components of freshwater and marine plankton. The stramenopiles are distinguished by their two types of flagella, one of which is covered with hair-like projections making it 'hairy,' while the other is smooth. Diatoms often reproduce asexually, but sexual reproduction and sporulation occur in some species as well.
In terms of pigmentation, photosynthetic stramenopiles like golden algae, brown algae, and diatoms contain chlorophyll a, chlorophyll c1/c2, and fucoxanthin, which are photosynthetic pigments. Their primary storage carbohydrate is chrysolaminarin. While diatoms boast frustules made of crystallized silica, brown algae and other stramenopiles display diverse morphologies, ranging from single cells to large multicellular kelps, and do not have a common phylogeny indicating that their photosynthetic abilities were acquired independently through secondary endosymbiosis.