Primary consumers are organisms that feed directly on producers, which are typically plants or algae. They are the first level of the food chain and play a crucial role in transferring energy from producers to higher trophic levels. In both aquatic and terrestrial ecosystems, primary consumers can include a variety of organisms.

In the given options, the correct answer is option 'A', which includes zooplanktons, frog tadpoles, snails, and tortoise as primary consumers in aquatic or terrestrial ecosystems.

Aquatic Ecosystem:
In an aquatic ecosystem, primary consumers are usually small organisms that feed on algae or other aquatic plants. They can be found in freshwater bodies like lakes, rivers, and ponds, as well as in marine environments like oceans and seas.

1. Zooplanktons: These are small, drifting organisms that include tiny animals like rotifers, copepods, and krill. They feed on microscopic algae and are an essential food source for many larger aquatic organisms.

2. Frog tadpoles: Tadpoles are the larval stage of frogs and are herbivorous or omnivorous, depending on the species. They feed on algae, plants, and detritus found in the water.

3. Snails: Aquatic snails are often found in freshwater environments and feed on algae, detritus, and decaying plant matter. They play a role in nutrient cycling and are an important food source for many predators.

Terrestrial Ecosystem:
In a terrestrial ecosystem, primary consumers can include a variety of organisms that feed on plants or plant material. They are found in habitats such as forests, grasslands, and deserts.

1. Zooplanktons: In some cases, zooplanktons can also be found in terrestrial ecosystems, such as temporary pools or wetlands. They feed on algae and other microscopic organisms present in these habitats.

2. Frog: Frogs are amphibians that can be found in various terrestrial habitats. They are insectivorous and feed on a wide range of invertebrates, such as insects, spiders, and worms.

3. Grasshoppers: Grasshoppers are herbivorous insects that feed on grasses and other plant material. They are commonly found in grasslands and can be an important food source for predators.

4. Hydra: Hydras are small, predatory animals found in freshwater habitats. They feed on small invertebrates, such as water fleas and mosquito larvae.

In conclusion, the primary consumer category in aquatic or terrestrial ecosystems includes zooplanktons, frog tadpoles, snails, and tortoise. These organisms play a vital role in energy transfer and nutrient cycling within their respective ecosystems.