Description: Thallus slightly flattened, without branches and frequently spirally twisted, ribboin-like. Attached by rhizoidal filaments growing to 8 cms long and no more than 0.5 mm broad.

Habitat: Infrequent. Epilithic in the upper littoral.

Distribution: Apparently on eastern shores of the British Isles. Europe: southern North Sea, Germany and Iceland.

Key Identification Features:

• Unbranched, flattened and spirally twisted.

Distribution Map from NBN: Petalonia filiformis at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Petalonia filiformis at iNaturalist World Species Observations database.

WoRMS: Petalonia filiformis at World Register of Marine Species. Accepted name: Planosiphon filiformis (Batters) Santiañez & Kogame, 2013. AphiaID: 1310311.

Classification: Biota; Chromista; Harosa; Heterokonta; Ochrophyta; Phaeophyceae; Fucophycidae; Ectocarpales; Scytosiphonaceae; Scytosiphoneae; Petalonia