Diatoms are unicellular eukaryotes placed under kingdom Protista; they are the primary photosynthetic producers in marine food chains and store their food as oil and polysaccharide leucosine. Thus, the correct answer is option C.  

Oils and leucosine are characteristic stored food in Dinoflagellates, Euglenoids, and Diatoms.

Dinoflagellates:
- Oils and leucosine are stored as characteristic food reserves in dinoflagellates.
- Dinoflagellates are a group of unicellular protists that are mostly marine organisms.
- They have a unique structure called a dinokaryon, which contains two distinct nuclei.
- Dinoflagellates are known for their ability to photosynthesize, but they can also ingest food particles.
- Oils and leucosine serve as energy reserves in dinoflagellates, providing them with a source of energy during periods of low light or nutrient availability.

Euglenoids:
- Euglenoids are another group of unicellular protists that are commonly found in freshwater environments.
- They have a unique structure called a pellicle, which is a flexible outer covering that allows them to change their shape.
- Euglenoids are capable of both photosynthesis and phagocytosis, meaning they can produce their own food through photosynthesis or consume other organisms for nutrients.
- Oils and leucosine are stored as characteristic food reserves in euglenoids, providing them with a source of energy during periods of low light or nutrient availability.

Diatoms:
- Diatoms are a type of unicellular algae that are commonly found in marine and freshwater environments.
- They are known for their intricate cell walls made of silica, which give them a unique appearance under a microscope.
- Diatoms are photosynthetic organisms and are an important part of the marine food chain.
- Oils and leucosine are stored as characteristic food reserves in diatoms, providing them with a source of energy during periods of low light or nutrient availability.

None:
- The option 'None' is incorrect because oils and leucosine are indeed characteristic stored food in dinoflagellates, euglenoids, and diatoms.
- These organisms rely on these stored food reserves to survive in challenging environmental conditions.
- The presence of oils and leucosine as stored food reserves is a defining characteristic of these groups of organisms and plays a crucial role in their survival and ecological roles.

Because there is no oil and leucosine in this dinoflagellates euglenoid and diatoms