What is the antennule?

The first pair of antennae in crustaceans; often reduced or absent in adult decapods, but frequently complex and multi-segmented in shrimp, copepods, and some other crustaceans. Crustaceans have two pairs of antennae on their heads. The first pair are called antennules, and the second pair are called antennae.

The antennules are the anteriormost pair of antennae in crustaceans. They are typically smaller than the antennae and are used for a variety of purposes, including:

* Sensing the environment: The antennules are equipped with a variety of sensory receptors, including chemoreceptors, mechanoreceptors, and proprioceptors. These receptors allow the crustacean to detect changes in its environment, such as the presence of food, predators, or mates.

* Communication: The antennules are also used for communication between crustaceans. They can be used to send signals about the crustacean's identity, reproductive status, and aggressive intentions.

* Feeding: Some crustaceans use their antennules to capture and manipulate food. For example, copepods use their antennules to filter small particles of food from the water.

The antennules vary in structure depending on the species of crustacean. In some species, the antennules are simple and unbranched, while in others they are complex and multi-segmented. The antennules may also be armed with spines, setae, or other structures.