Hornlets

Hornlets are small horn-like outgrowths observed on the exterior of various organisms, typically measuring a few millimeters or less. The term is descriptive and non-taxonomic, derived from horn and the diminutive suffix -let.

Morphology varies: they can be conical, curved, or flattened; made of keratin, chitin, or mineralized material; and may have smooth or ridged surfaces. Most hornlets are sessile and project from the cuticle, with a base that blends into the surrounding integument; in some taxa they are articulated to allow slight movement.

Hornlets occur in multiple invertebrate groups and are less common in vertebrates, where comparable structures are rare and usually larger. Possible functions include signaling to mates or rivals, camouflage or disruptive coloration, defense against small predators, or aiding in movement through complex habitats; however, functional evidence is limited and often species-specific.

Developmentally, hornlets arise from epidermal tissue during juvenile stages and may persist into adulthood; growth is generally limited and restricted to the local integument. Because hornlets show considerable variation, they are primarily used as descriptive characters in morphological literature rather than as diagnostic traits for higher taxa.