spiral wrack

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spiral wrack (twisted wrack) The common name for the brown seaweed Fucus spiralis (see FUCUS). The thallus differs from that of bladder wrack (F. vesiculosus) in lacking air bladders, and from that of serrated wrack (F. serratus) in that the margins are not serrated; the branches are usually somewhat twisted spirally. It is found attached to rocks rather higher on the shore than other Fucus species.