Final answer:
The largest living unicellular organism is Caulerpa taxifolia, a thallus of a marine algal species that belongs to the seaweed group. It can grow several meters in length and is composed of a single cell that can divide and form new branches.
Step-by-step explanation:
The largest living unicellular organism is known as the thallus of a marine algal species called Caulerpa taxifolia. It belongs to the group of algae known as seaweed and can grow up to several meters in length. This organism is composed of a single cell that can divide and form new branches, giving it a multi-cellular appearance.
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