Fucus filiformis

Chorda filum have typically long, unbranched and hollow rope-like brown fronds about 5 mm (0.20 in) in diameter but can reach to lengths of 8 m (26 ft). The holdfast is disc-shaped. C. filum is found in sheltered marine and estuarine bodies of water at depths of up to 5 m (16 ft). They are usually anchored to loose substrates like gravel and pebbles or other macroalgae and eelgrass. C. filum grow at an average of 17 cm (6.7 in) per month, with the spiral-shaped, often gas-inflated, termini of fronds being dead, but receiving replacement by growth from a sub-terminal meristem. They are annuals, and die during winter. The fronds bear short colorless hairs in summer. Chorda filum is similar to Halosiphon tomentosus. However H. tomentosus is less common and is covered with long brown paraphyses or sterile hairs.

Chorda filum is to be found in very sheltered shores. It may be common or abundant near low water and in the sublittoral to 25 m (82 ft) areas in mud and sand.