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The Seashore

Rough Periwinkles

Rough Periwinkles

For many years the rough winkle was thought to be a single species (Littorina saxatilis). Then taxonomists divided it up into several species. Then they put some of them back into the species saxatilis. Who knows what they'll do next? There are several closely related species and sub-species that we call rough winkles. The taxonomy is very tricky and best left to specialists. If you've got snails that look alike and they are all in one bit of shore you can probably treat them as all the same species. The ones above are L.saxatilis.

They do have some interesting features that allow them to survive high up on the shore and into the splash zone. They have a shell, they breathe air using their mantle cavity as a lung, they can excrete uric acid as a nitrogenous waste (not very toxic so can be excreted almost as a solid, saving water). They are ovoviviparous (retain their egg inside the shell until it hatches so the babies already have a shell when they emerge) and so avoid the plankton. They can aestivate. In very dry conditions they glue themselves on to the rocks with mucous and withdraw into their shell, closing the door (operculum) behind them. Very handy if you live high up on a seashore. They can also move about and so select appropriate moist microhabitats like cracks and crevices. However, it is thought that during their lives they do not stray very far.

If you can survive the difficult abiotic environment up here in the splash zone and upper shore there are some advantages. Little interspecific competition for instance and lots of food (if you like lichens which luckily they do)

The species below is one of the rough periwinkle group (reliably identified by Dr John Graham, University of Leeds) as Littorina compressa. It is all very tricky stuff!

L. compressa

See also Melaraphe (small winkle), Flat winkles and L. littorea (Edible winkle)

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