Chorda filum (Linnaeus) Stackhouse
Description: Thallus cylindrical, dark brown, to 10 m long (mostly 2-6 m when mature). Frond unbranched, 5mm wide; parenchymatous, differentiated into a cortex, medulla and small celled epidermis; elongate medullary hyphae present; solid, becoming hollow in older plants. Frond covered by clavate unicellular paraphyses and colourless hairs; attached by a discoid holdfast. Unilocular sporangia formed among paraphyses over the surface of the frond. Fronds often wound together in rope-like masses.
Habitat: Grows on smalls stones and gravel in the lower intertidal and shallow subtidal; sometimes epiphytic.
Photographs © M.D. Guiry