Which aquatic plant is identifiable by its dark green leaves arranged in whorls and anchored in sediment?

The correct identification of the aquatic plant is related to its specific characteristics. The plant in question, identifiable by dark green leaves arranged in whorls and anchored in the sediment, aligns with the description of coontail.

Coontail, or Ceratophyllum demersum, is characterized by its feathery, whorled leaves that are typically dark green, and it often forms dense stands in water bodies. It is a submersed plant that does not have true roots but is anchored in sediments through its structure, which allows it to thrive in aquatic environments.

In contrast, filamentous algae do not have a defined leaf structure like vascular plants and instead appear as green, thread-like structures that can float or drift in water. They do not possess whorled leaves or a rooting system, making them distinct from coontail and other vascular aquatic plants.