Antennules

Antennules are the paired, typically anterior appendages found in many crustaceans, commonly referred to as the first antennae. They are usually shorter and more slender than the second pair of antennae and arise near the mouthparts. The structure and length of antennules vary among groups, but they are generally segmented and bear numerous sensory setae (hairs). In many species, the base of the antennule houses a statocyst, a balance organ that helps the animal orient itself in the water.

The primary function of antennules is sensory. They provide chemosensory input, detecting chemical cues in the environment that relate to food, mates, or danger. They also carry mechanosensory receptors that respond to touch and water movement. This sensory input supports navigation, prey detection, and social and environmental assessment. In addition, the presence of a statocyst at the base of the antennule contributes to balance and spatial orientation in the aquatic medium.

Development and variation of antennules are often used in crustacean taxonomy and phylogeny. Across taxa, antennules can differ in segmentation, setation (arrangement of sensory hairs), and the presence or absence of internal sensory organs. Their morphology provides information useful for identifying groups and understanding evolutionary relationships.

See also: Antennae; Statocysts; Chemo- and mechanoreception in crustaceans.