aculeus
From ZooTerms (Dictionary of Invertebrate Zoology)
aculeus (noun; plural aculei; Latin diminutive acus, needle): (Arthropoda: Insecta) 1. In Hymenoptera, an ovipositor in the form of a sting. 2. In Diptera, a sharp spine projected from the margin of the eighth sternite of Tipulidae.
