Phylum: Rhodophyta   Family: Hapalidiaceae

Choreonema thuretii (Bornet) F. Schmitz, 1889

"Thallus consisting of simple or branched articulated filaments, penetrating the tissues, and bearing fructifications on the surface of the host" - Newton.
A warm water parasitic alga, not uncommon on the south coast. This would appear to be the second Scottish record (2016)

References: 
Newton (1931) - A Handbook of the British Seaweeds;
Irvine & Chamberlain (2011) - Seaweeds of the British Isles, Volume 1 Rhodophyta, Part 2B Corallinales, Hildenbrandiales