The "fingers" are branches up to a centimeter wide and sometimes over 30 centimeters long.

Codium fragile occurs in the low intertidal zone, and subtidal on high-energy beaches.

It has no asexual (sporophyte) stage, and male and female gametes are both produced on separate plants.

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Codium fragile subsp. atlanticum is known to have arrived in the southwest of Ireland around 1808. From there it may have spread by rafting or floating in the sea. Approximately 30 years later, it was found in Scotland. It is thought to have originally come from the Pacific Ocean near Japan.

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This species displaces the native Codium tomentosum.