labium
From ZooTerms (Dictionary of Invertebrate Zoology)
2. (Arthropoda: Chelicerata) In Araneae, the lower lip, forming the floor of the mouth cavity.
3. (Arthropoda: Crustacea) The metastoma.
4. (Arthropoda: Insecta) One of the mouth-part structures, the lower lip, composed of fused second maxillae; has been referred to as the tongue at a certain phase of development.
5. (Mollusca) The inner lip of a univalve shell, the inner side of the aperture or columellar lip extending from the origin at the lip of the labrum and resting on the columella
See also: inner lip.