Caulerpa is a genus of seaweeds in the family Caulerpaceae (among the green algae). They are unusual because they consist of only one cell with many nuclei, making them among the biggest single cells in the world.

Referring to the crawling habit of its thallus, the name means 'stem (that) creeps', from the Ancient Greek kaulos (καυλός, 'stalk') and herpo (ἕρπω, 'to creep').

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