Wiping just ceased; mucus gland partly visible in gap (1) between two sides of dorsal crest of metapodium.
C. zizyphinum feeds on micro-algae and other micro-organisms scraped by its radula from rocks and stones, and by “shell wiping” (about 20% of intake) (Jones, S.P. et al., 2001) . Twice every 24 hours its metapodium (“tail”) is extended with its crest opened to expose a mucus-producing area which it wipes over the shell for about 20 minutes. The coated shell acts like a fly paper trapping micro-organisms and other water borne particles which are ingested along with mucus. This behaviour operates most effectively in strong currents loaded with particles; C. zizyphinum is often large and abundant in marine rapids.This specimen is on a vertical rockface where it is exposed to water movement of a large swell. Shell wiping usually maintains the shell free of fouling by epizooic growths (but not always www.bioimages.org.uk/html/r164639.htm ), and is the cause of live shells sometimes feeling slippery.
Sublittoral, 8 m, on vertical rockface. Rosehearty, Scotland. November 2018 © C. Rickard