Final answer:
Decomposers and detritivores are not included in the described food web and are essential for recycling nutrients and matter within ecosystems, aiding in the maintenance of energy flow.
Step-by-step explanation:
Organisms that are not included in the example of a grazing or detrital food web and that can enter at any point are decomposers and detritivores. Decomposers, such as bacteria and fungi, play the critical role of breaking down dead and decaying organisms, thereby releasing nutrients back into the environment and supporting the biotic part of the ecosystem. Detritivores, like certain invertebrate animals, consume organic detritus contributing to the similar process of nutrient cycling.
These organisms effectively recycle energy and matter, ensuring the continuation of the food web. Without them, nutrients would remain locked in non-living matter and not be accessible to the living components of the ecosystem.