The Behaviour of Littorina Littorea (L.) Under Natural Conditions and its Relation to Position on the Shore

Extract

On the flat shore at Whitstable the population of common winkles is distributed appreciably at random over a variety of substrata ranging from wooden groynes, through shingle to muddy sand, between tidal levels corresponding to H.W.N.-E.L.W.S. but with a maximum density near M.T.L., although aggregations tend to occur in wetter situations and where planking joins vertical groyne posts.

Observations on winkles marked with a dab of paint of distinctive colour show that they tend to remain in approximately the same position for many weeks.

For most of each tidal period winkles remain settled in situations such as stones or groynes, which provide good holding ground, but as the tide recedes or the incoming tide reaches them, they become activated to crawl, feeding meanwhile. These feeding migrations are recorded in the sand by roughly U-shaped tracks and can be seen under favourable circumstances as similar tracks in the vertical plane for winkles on groynes. By such excursions the animals are enabled to move, feed and return to approximately the place from which they started and this serves to explain how they maintain their station on the shore.

When settled on vertical surfaces, winkles always orientate with the head uppermost, when the foot may be withdrawn and the animal become attached by a film of dried mucus.

When crawling the eyes are exposed and the tentacles bend to test the substratum, but only that part of the tentacle distal to the eye bends so that the optical axis of the eye maintains a constant angle to the body axis.