lunule
From ZooTerms (Dictionary of Invertebrate Zoology)
lunule (noun; Latin diminutive luna, moon): 1. A crescent-shaped part or marking.
2. (Arthropoda: Crustacea) In Copepoda, small, sucker-like adhesion disc on the anterior margin.
3. (Echinodermata: Echinoidea) One of several perforations in the test of some sand dollars that may serve for passage of sand and water while burrowing.
4. (Mollusca: Bivalvia) Cordate shaped depression anterior to the beaks.
