Periwinkles
The Periwinkles are a group of both very common, but also quite rare species of marine snails. They are all herbivores, feeding on algae and the main species, below can be seen to differ just on what they tend to feed on (the smaller species feeding on the tougher algae lower on shore).
Here you will be introduced to the most common periwinkles we find on Shoresearches. You will be given several ID features to look for and an understanding of something of their ecology.
This should help your ID too.
The species in focus are:
edible periwinkle/gwichiad (Littorina littorea)
flat periwinkle/gwichiad y gwymon (Littorina obtusata/fabalis)
rough periwinkle/gwichiad garw (Littorina saxatilis)
You will see what they look like in different situations and understand how to separate them from other commonly found molluscs.
You will then be tested.
Now you’ve been introduced to some of our more common periwinkles we’ll introduce you to some of the comparisons to keep an eye out for. These are amongst the periwinkles, but also include shells which can look a bit similar in certain situations.
The edible periwinkle can easily be confused with the toothed topshell. They are a similar size. When dry, they look grey-ish, when wet they can look dark in colour. The differences are:
- The toothed topshell has a rounded, flattened spire
- The edible periwinkle does not have coloured patterning – it has faint ridges running parallel to the whorls
- The toothed topshell has pearlescence on the spire
The rough periwinkle and edible periwinkle, when young, can look similar. When they’re a similar size they both can have clear ridges on the outside of their shell.
- The rough periwinkle’s opening (aperture) is all one colour, the edible periwinkle has a clear white/cream column and striped brown outer edge.
- The rough periwinkle can often be pale in colour
- The rough periwinkle is unlikely to be seen lower on the shore
- The rough periwinkle’s opening outside border can be thickened.
Flat periwinkles tend to not be confused, but might be tricky to find as many can be camouflaged, so keep an eye on tricky colour forms, like the ones above.
Peruse the periwinkles
edible periwinkle/gwichiad (Littorina littorea)
©North Wales Wildlife Trust
- up to 5cm high
- ridges (fine in older shells)
- relatively large, intertidal shell
- pointed spire (sometimes paler than rest of shell)
- most often brown-black or dark grey but can be red or striped
- may tuck into crevices in hot or windy weather
- in juveniles the central axis of the shell is white at the opening and the rounded part of the aperture is striped brown
- tentacles (if seen) has black stripes
- can be seen across all shore heights
- may tuck into crevices in hot or windy weather
rough periwinkle/gwichiad garw (Littorina saxatilis)
©North Wales Wildlife Trust
- up to 1.8cm high and 1.4cm in diameter
- relatively deep ridges
- small to medium-sized intertidal shell
- can be yellow, green-ish, brown and red, commonly has a different-coloured spire area
- very small specimens can be found inside empty barnacle shells
- likes high shore
- pointed spire
- no colour difference at aperture (shell opening)
flat periwinkle/gwichiad y gwymon (Littorina obtusata/fabalis)
©North Wales Wildlife Trust
- one of two different species which it is thought cannot be identified to species in the field
- up to 1.5cm high
- sometimes seen striped, but most often one colour (can be brown, grey, black, yellow, orange, green) and no patterns
- small intertidal shell
- likes living on and around algae, especially the wracks
- spire is flat (the last whorl, ending in aperture, is about 90% of the total shell) seen from mid shore down
- lays eggs on wrack fronds in circular jelly blobs
Alternative factoids
Want to get to know more about your winkles? This section will not appear in the quiz as questions.
The flat periwinkle often looks a striking yellow colour, but it is thought that this colour is most often associated with serrated wrack, which, underwater is seen as being yellow. This small yellow molluscs, therefore, remains as camouflaged as the brown coloured individual is when sat next to a bladder wrack bladder.
The rough periwinkle has a very wide global distribution including both sides of the Atlantic.
The edible periwinkle has been introduced to the East coast of the U.S.A. it is thought by the Vikings, as food species and is considered an invasive species in some areas.
The edible periwinkle is called that because it is the animal eaten as “winkles”.
The next section is the quiz. You will be tested on what you’ve learnt so far. Don’t worry too much, as once you’ve been out on the shore, the ID features you’ve learnt about will make more sense and after a couple of visits you should feel more confident about your ID.
Good luck!