The ascidian Aplidium conicum from Tarifa Island contains the four new meroterpenoids conidione (1), conicol (2), 2-[(1'E)-3'-methoxy-3',7'-dimethylocta-1',6'-dienyl]benzene-1,4-diol (3), and conitriol (4) together with five related known compounds (5-9). It is proposed that the nonaromatic compound conidione (1) was derived by cyclization of an intermediate conitriol quinone 11. The structures of the new compounds were elucidated by interpretation of spectral data.