From ZooTerms (Dictionary of Invertebrate Zoology)
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apex (noun; plural apexes, apices; Latin apex, tip): 1. That portion of any structure opposite the base of attachment; the tip.

2. (Arthropoda: Crustacea) The upper angle of the scutum or tergum of certain barnacles.

3. (Arthropoda: Insecta) Wing tip.

4. (Mollusca) a. In Polyplacophora, the beak or umbo of a valve. b. In Gastropoda, the first-formed end of a shell.