1. Phytoplankton: These are microscopic algae that float freely in the water column. They are the most abundant primary producers in the oceans and freshwater lakes and rivers. Examples include:

* Diatoms: Single-celled algae with intricate silica cell walls. They are a major contributor to primary productivity in both marine and freshwater systems.

* Dinoflagellates: Single-celled algae with two flagella, which allow them to move through the water. Some species are responsible for harmful algal blooms (red tides).

* Cyanobacteria: Photosynthetic bacteria that can produce oxygen. They play a significant role in both freshwater and marine environments, and some species can fix nitrogen from the atmosphere.

2. Macroalgae (Seaweed): These are larger, multicellular algae that are typically attached to surfaces like rocks or seafloor. They are found primarily in marine environments. Examples include:

* Green algae: Mostly found in freshwater, but some species are adapted to marine environments.

* Brown algae: Common in colder, temperate waters and include species like kelp.

* Red algae: Can live in deeper water due to their ability to utilize different wavelengths of light.

3. Aquatic plants: These are plants that are adapted to living in water. They can be found in both freshwater and marine environments. Examples include:

* Water lilies: Floating plants with large, round leaves.

* Cattails: Emergent plants that grow in shallow water.

* Seagrass: Submerged plants that form meadows on the seafloor.

It is important to note that the specific types of photosynthetic autotrophs found in a given aquatic environment will vary depending on factors such as:

* Water depth: Light availability decreases with depth, so different types of algae are adapted to different light levels.

* Water temperature: Some algae prefer warmer waters, while others prefer colder waters.

* Nutrient availability: The availability of nutrients like nitrogen and phosphorus can influence the abundance and types of algae present.

These diverse photosynthetic organisms are crucial to the functioning of aquatic ecosystems, as they provide the base of the food chain and produce oxygen for other organisms.