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 are not.
Arthropoda (Phylum) > Crustacea (Subphylum) > Hexanauplia (Class) > Thecostraca (Subclass) > Sessilia (Order) > Balanidae
(Family) > Balanus
(Genus) > trigonus (Species)
Marine, Intertidal to 55 metres