Phylum: Ochrophyta  Family: Tabellariaceae

Tabellaria flocculosa  (Roth) Kützing, 1844

Found in freshwater where the zig-zag filaments can be found loosely-attached to rocks and vegetation in the littoral zone or entangled in filamentous algae

References: 
Kelly et al. (2005). Common freshwater diatoms of Britain and Ireland: an interactive key