Codium fragile

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 of two subspecies in Great Britain and Ireland. They are similar, both are dark green in color. It forms long erect finger-like fronds. These grow to 40 cm or more long branching dichotomously. The cortex of the branches is formed by closely packed utricles, these are small cylindrical club-shaped structures formed from a single cell up to 1200µm (micrometre) long.The rounded tips of these colosely packed utricles give the frond a velvety texture. The fronds 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.