Periwinkles (Littorina)

Contributed by Bonnie Becker


Where found:  Uppermost horizon, as far as possible from the sea, but close enough to wet gills occasionally.

Interesting facts:  These creatures have distaste for seawater and it is believed that they are in the evolutionary process of changing from sea to land dwellers (BPT).

Adaptations:   Very resistant to terrestrial conditions. In the lab, they have survived immersion in fresh water for days. They have also been fed to anemones in the lab and have reemerged alive and healthy. The way they are able to do this is by closing their operculum, a hard “door” that closes them tight into their shell. When shut into their shell, they can retain moisture and keep out wind and freshwater, as well as anemone digestive juices. When their operculum is closed, they can’t use their strong foot to attach to the rocks. Instead they secrete mucous along the aperture of the shell that serves as glue.

Food:  All marine snails have a radula, a hard ribbon containing rows of file-like teeth. Some snails use this to drill into crustacean’s or other mollusc’s shells, but the Littorina use it to scrape off detritus and tiny plants off the almost-bare rocks. The activities of the Littorina can cause erosion of the rock face. They can go for long periods of time without food.

Reproduction:  Individual Littorina can follow the mucous trail of other’s movements, which allows them to find mates. They will copulate any time of the year, but will do it en masse in spring and summer. Eggs are laid in elongate, gelatinous masses in the rising tide. After a few hours of immersion, the egg masses disintegrate, liberating thousands of separate eggs, each in its own capsule. Swimming veliger larvae emerge in 2-9 days. 

Phylum:           Mollusca (Soft-bodied animals with external shells or modified internal shells)
Class:              Gastropoda (Snails, Limpets, Sea hares, Nudibranchs, etc.)
Subclass:         Prosobranchia
Order:             Mesogastropoda (Periwinkles, Slipper shells, Cowries, Moon snails, Horn shells, etc.)

The Littorines or Periwinkles

  • One of the highest intertidal beasts
  • Capable of herculean feats of endurance
  • Similar species common in high rocky intertidal habitats throughout the world
  • Very common and responsible for significant erosion at Cabrillo




Littorina Keenae


  • The first organism most people will find
  • Can survive for months out of water
  • Can survive ingestion by many would be predators
  • Feeds on diatoms and microalgae, eventually eroding the rock away.
  • Uses mucous to stick to rock while avoiding exposure

Flat bench-like area

This is L. keenae. The lack of the flat bench is indicative of L. scutulata.
  • Practically terrestrial
  • Survives in air for months
  • Impermeable seal btween shell & operculum
  • Very common
  • Grazer
  • Responsible for considerable erosion
  • Up to 18 mm

Littorina scutulata


  • Found lower than keenae, but still fairly high.
  • Often speckled, but color is not a dependable trait.
  • Can erode rocks up to 1 cm every 16 years

No bench-like areaPeriwinkles

  • Found a bit lower than L. keenae
  • Less robust then L. keenae, but can still survive in air for weeks
  • Very common
  • Up to 13 mm
  • Grazer
  • Slimmer & more conical then L. keenae

Last revised 15-Aug-13