Codium fragile, known commonly as green sea fingers, dead man's fingers, felty fingers, forked felt-alga, stag seaweed, sponge seaweed, green sponge, green fleece, and oyster thief, is a species of seaweed in the family Codiaceae. It originates in the Pacific Ocean near Japan and has become an invasive species on the coasts of the Northern Atlantic Ocean.

This siphonous green alga is dark green in color. It appears as a fuzzy patch of tubular fingers. These formations hang down from rocks during low tide, hence the nickname "dead man's fingers". 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.