Which two types of filamentous algae exist in aquatic environments?

Filamentous algae are a common type of algae that can be found in various aquatic environments. The correct answer identifies two types of filamentous algae based on their growth habits: attached and planktonic.

Attached filamentous algae grow anchored to surfaces such as rocks and submerged plants. This growth habit allows them to thrive in areas where they can obtain sufficient sunlight for photosynthesis while also benefiting from the stability provided by the substrate.

On the other hand, planktonic filamentous algae, while often less common, refer to those that float freely in the water column. These algae are capable of drifting and can spread over large areas due to water currents. This category of filamentous algae sometimes forms blooms, contributing to the overall productivity of aquatic ecosystems.

The other options do not accurately represent the types of filamentous algae. For instance, the terms "free-floating" and "rooted" may refer to other aquatic plants or forms of algae but do not specifically classify filamentous algae in the standard terminology used to distinguish their growth forms.