Top shells
Top shells can be found in abundance on our shores. They can be tricky to get to know, so there are a few key features to look for and keep an eye on where you are on the shore, as that will also help you to understand what you’re likely to be looking at.
Here you will be introduced to the most common top shells 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:
toothed top shell/top-môr trwchus/Phorcus lineatus
grey top shell/top môr llwyd/Steromphala cineraria
purple top shell/top-môr porffor/Steromphala umbilicalis
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 seen some of our topshells we’ll introduce you to some of the comparisons to keep an eye out for. These are amongst the topshell group, but also those shells which can look a bit similar in certain situations, especially as you begin your Shoresearch Cymru volunteering.
The edible periwinkle can easily be confused with the toothed top shell. They are a similar size. When dry, they look grey-ish, when wet they can look dark in colour. The differences are:
- The edible periwinkle has a pointed spire
- The edible periwinkle does not have coloured patterning – it has faint ridges running parallel to the whorls
- The edible periwinkle does not have pearlescence on the spire
The purple top shell can also be confused with the toothed top shell. They can look similarly colourful and apart it is difficult to compare the size differences. The differences are:
- The purple top shell is smaller as an adult
- The toothed top shell has a zig-zag patterning and not stripes (you might need to look closely on dried shells)
- The toothed top shell mostly likes living higher up the shore
The purple top shell can be confused with the grey top shell. They are similar in size, but not quite in shape. The differences are:
- The grey top shell has a taller spire – the alternative name for the purple top shell is the flat top shell and that’s due to it’s flattened spire.
- The grey top shell has stripes. but they are closer together and thinner in appearance and are less colourful, usually grey and cream-white, but sometimes a bit pinkish.
- The grey top shell has a tendency to be seen lower down on the shore.
Top shell recap
toothed top shell/top môr trwchus (Phorcus lineatus)
©North Wales Wildlife Trust
- up to 3cm high and 3 cm in diameter
- zig-zag patterning
- relatively large intertidal shell
- likes high shore
- pearlescent spire
- if in doubt, carefully look for the tooth (a small lump on the shell opening – aperture)
- may tuck into crevices in hot or windy weather
purple top shell/top môr porffor (Steromphala umbilicalis)
©North Wales Wildlife Trust
- up to 1.5cm high and 2.2cm in diameter
- striped patterning
- small to medium-sized intertidal shell
- likes mid-low shore
- pearlescent and flattened spire
- stripes and spaces in between are thick
- always has an umbilicus
grey top shell/top môr llwyd (Steromphala cineraria)
©North Wales Wildlife Trust
- up to 1.5cm high and 1.7cm in diameter
- striped patterning
- small to medium-sized intertidal shell
- likes low shore
- pearlescent spire
- stripes and spaces in between are thin
- spire is tall, but not pointed
- doesn’t always have an umbilicus
Alternative factoids
You might be keen to know a bit more about the three molluscs you’ve been studying so far. This section will not appear in the quiz as questions.
The toothed top shell is one of the Climate Change Indicators you’ll be learning more about whilst taking part in Shoresearch Surveys. This species is thought to be moving northwards as our seas are becoming generally warmer.
More species of top shell can be seen on our shores (over 70 species in Europe), but are either less commonly found or are found on sandier shores.
The purple top shell has a western distribution in Northern Europe, so your not likely to see it in the North or Mediterranean seas.
There is another Citizen Science Survey (external site link here) looking at the toothed and purple top shells as well as the dog whelk to see whether certain molluscs are using man made sea defences to leapfrog along the coast in response to Climate Change.
The next section is the quiz. Click to begin the quiz, the questions will appear below. For the fill-in-the-gaps questions, make sure you spell the same way as the word/phrase in the list, but don’t worry about using capitals or not. If you get any one question wrong within each quiz page, the you will be marked as wrong for the whole page. Answers will appear one you’ve finished each question.
You will be tested on what you’ve learnt so far using the reading and video info. 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!