Thursday, May 3, 2012

The Little Shuffler

Whinless Down is a remnant of chalk downland on the edge of Dover.


Standing at the top of the down there are panoramic views up the valley (the houses of Elms Vale on the left)...


...and turning round, towards Dover and the Channel, with Dover Castle perched on the hill in the distance.


Despite the grotty weather, in some brief sunny spells, where there was shelter from the blustery wind, I saw a couple of green hairstreaks....


...and a few dingy skippers; this one nectaring on Cyprus spurge Euphorbia cyparissias, a non native species which is pretty abundant on parts of Whinless Down. The bright yellow-green of the Euphorbia was striking and it smelt like honey. It was certainly attracting bees and butterflies.


I walked along this muddy path (carefully avoiding the dog poo) on the lower edge of the down.


Shuffling across the path in front of me were these delicate, elegant little snails (they're about 1cm tall).


Let me introduce a very special snail; Pomatias elegansthe round mouthed snail or land winkle. They are not only utterly, stunningly gorgeous but absorbingly fascinating ecologically. This is a dapper little animal with very attractive reticulated patterning on its whorled shell.


If you turn one over, you find something very unusual; an operculum...


...Pomatias is from the Greek poma, a lid or covering. The operculum is a hard flat shell attached to the snail's foot. It covers the 'round mouth' (the shell aperture) and seals the shell tight shut if the snail is threatened or when dormant to prevent dessication. The operculum in Pomatias is hard and, for its size, pretty thick. The picture below was taken a few months back of some empty shells we found in Park Wood, near Chilham.


Pomatias is distinctly different from most common or garden snails we find in the UK. Land snails do not have operculums (or opercula). Hmmm.

The classification (taxonomy) of land snails is complex and ever changing (see Wikipedia on the subject here). My head aches just thinking about it and I've had to read about it to write this blog post. There are 2 main groups of land snail; Pulmonates (the vast majority of our land snails) and Prosobranchs. Pulmonates share a common lineage but prosobranchs are a more heterogenous group. Little Pomatias is a prosobranch, related to the marine periwinkes (recall that it's called the land winkle).

Here's a quick comparison of our typical terrestrial snails and Pomatias...

Most land snails                     Pomatias elegans
No operculum                          Has an operculum
2 pairs of tentacles                  Single pair of tentacles
Tentacles retractable               Tentacles not retractable
Eyes on tentacles                     Eyes at base of tentacles

In addition most land snails are hermaphrodite and Pomatias has separate sexes. Pomatias also has a long trunk or proboscis, which it uses to move. So it doesn't crawl like other snails, it shuffles. It's actually called The Shuffler.


Zooming in closer the 'trunk', eyes, single pair of tentacles and operculum, are all visible.


It's simply lovely to watch it shuffling along a path.

video

(The background clicking noise and the 'in & out of focus' effect is my Fuji Finepix auto-focussing. 
The shakiness and jabbering is me.)

There are actually only 2 species of operculate land snails in the UK (although operculate snails are more numerous in the tropics). Our little Shuffler and Aciclua lineata, an incredibly teeny (2-4mm) snail which lives in wet moss. I've never seen one.

Picture of Aciclua lineata from Wikipedia

According to the Kent Red Data Book it favours woodland leaf litter in the south of England. I'll have to go and look for it :-)

Our shuffling snail lives preferentially on chalky/limestone soils. It's also possibly a marker species for ancient hedgerows (see ref. here) on those soils. As with so many unusual and beautiful animals, this little snail is under threat from over-intensive farming. Downland is a rare habitat in the UK; so much of our downland has been ploughed up. Our lives would be so much the poorer without such wonders as The Little Shuffler.



More information on...

Whinless Down

A pdf leaflet (White Cliffs Countryside Partnership (WCCP)) for Whinless Down is available here.

WCCP run groups of conservation volunteers who help maintain vital chalk habitats in the Dover area. The timetable for spring/summer tasks is here.

The Kent Wildlife Trust acquire and manage chalk downland habitats in Kent.

Pomatias elegans
Snail's Tales, a blogger (Aydin Örstan) specialising in all things snail has excellent pictures of Pomatias elegans coming out of it's shell here. There are some more super pictures and information on The Wee Shuffler here.

The Mollusks: A Guide to Their Study, Collection and Preservation. Charles F. Sturm, Timothy A. Pearce, Ángel Valdés. I accessed Chapter 22 (Land Snails) co-written by Aydin Örstan (Snail's Tales blogger) here.

Watson, L. and Dallwitz, M.J. (2005 onwards). The families of British non-marine molluscs (slugs, snails and mussels). Version: 4th January 2012. Here and illustrations here.

The Living World of Molluscs was a mine of useful information which I used to write this blog.
Terrestrial snails
Round-mouthed snails
The tentacles of snails


11 comments:

  1. You see! That's what I mean about your posts being compelling. You make the tiniest subject fascinating and every little detail interesting. Studying a snail doesn't immediately sound exciting but you make it so. Well done Mel!

    I'm assuming there is a piece of video but unfortunately it's not showing, perhaps because I am on my iPad although that isn't usually a problem!

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  2. What a beautiful snail! Wish we had then up here in the North East.

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  3. Thanks. You are too kind.
    Hmmmm. I've tried to embed the video from my Flickr account...it works on my computer...but not on a friend's. Thanks for pointing out. I'll try again later when I get back from the pub :-)))

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  4. Re. the embedded video. I've reloaded the video directly into blogger (instead of trying to use my Flickr account which I erroneously thought would be easy) and, although it's a bit smaller than I wanted, it does seem to work now....I hope.....Mel

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  5. Hi Phil. Yes they are lovely little creatures. I'm quite enamoured. M

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  6. Hi, Mel. That's an interesting snail! I saw one for the first time last week, in the woods near One Tree Hill, but it didn't want to come out of its shell. It was the unusual proportions that caught my attention.
    Bill

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  7. Still no show on the video Mel which leads me to believe it is probably due to iPad not supporting Adobe flash. I will put the laptop on later and try again.

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  8. Drat and double drat. I deleted the original yesterday, which I'd tried to embed from Flickr, and uploaded directly into Blogger. It works on a friend's computer.

    I've fiddled about on Flickr again and the link is apparently http://flic.kr/p/bSQgGk

    Mel

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  9. Hi Bill. They are very distinctive aren't they. I need to go and see if I can tell male from female now :-)

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  10. A wonderful fascinating post Mel, I will be keeping an eye out for these as there are records of them found on the Burren just north of where we are staying.

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  11. I'm quite in love with them. M

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