Arsenicin A

Arsenicin A, As₄O₃(CH₂)₃ is a complex molecule containing four arsenic atoms in a cage-like structure. It's found in tiny quantities in the New Caledonian marine sponge Echinochalina bargibanti and is the first poly-arsenic compound to have been isolated from nature. Its role in the marine sponge remains unknown, partly because of the lack of detailed knowledge about the chemical structure.

Empirical formula: C₃H₆As₄O₃