Arculus

Definition

In insect wing morphology, a crossvein located near the base of the wing that connects the anterior cubitus (CuA) and the posterior cubitus (CuP), or their equivalents, forming an arched or bow-shaped structure. The arculus serves as a diagnostic character in the venation patterns of several insect orders, particularly Odonata (dragonflies and damselflies), where it represents a thickened, often pigmented crossvein that helps brace the wing base and influences the folding mechanism. Its presence, position, and morphology vary among taxa and are used in species identification and phylogenetic analysis.

Etymology

Latin arculus, diminutive of arcus (bow, arch), referring to the curved, bow-like shape of the vein.

Example

In dragonfly wings, the arculus appears as a strong, oblique crossvein between the cubital veins, with its shape and angle varying between families such as Aeshnidae and Libellulidae.

Synonyms

• arculus vein
• arculi crossvein

Related Terms

• crossvein
• cubitus
• anal vein
• nodus
• pterostigma
• venation
• wing coupling

Usage Notes

The term is primarily used in odonate systematics and paleoentomology, where wing venation provides critical taxonomic characters. In some literature, 'arculus' may refer broadly to any basal crossvein in the cubital region, but specialists restrict it to the specific CuA-CuP connection. Not to be confused with the unrelated bivalve genus Arculus (family Lasaeidae).