Balanus trigonus Darwin, 1854
This is not a Mollusc. Other non-Molluscan Phyla (Echinodermata, Brachiopoda etc) have been included to help identify species that may be mistaken for Mollusca, but actually are not.
Arthropoda (Phylum) > Crustacea (Subphylum) > Hexanauplia (Class)
> Thecostraca (Subclass)
> Sessilia (Order)
> Balanidae (Family)
> Balanus (Genus)
Marine. Intertidal to 55 metres