Phylum: Rhodophyta   Family: Rhodomelaceae

Choreocolax polysiphoniae  Reinsch, 1875

Thallus parasitic on Vertebrata lanosa. Apparently quite common but infrequently recorded

References: 
Irvine (1983) - Seaweeds of the British Isles, Volume 1 Rhodophyta, Part 2A Cryptonemiales (sensu stricto), Palmariales, Rhodymeniales