Joe Botting's picture

Balea perversa

Observed: 19th February 2013 By: Joe BottingInvertebrates expert
Balea perversa
Balea perversa (2)

About 8 mm long (maximum), in an old quarry (beneath stones). Found along with Oxychilus aliarrius, Discus rotundatus, Vertigo pygmaea and the usual Cepaea and Cornu.

Species interactions

No interactions present.


martinjohnbishop's picture

Juvenile Clausilia bidentata I think

Adult Balea would only have about 7 whorls and the lip would be slightly thickened. This has already 9 and the lip looks undeveloped.

andyk's picture


This looks like a juvenile and, as such, may not yet have developed the 'teeth'.

Andy Keay

Joe Botting's picture

Thank you both - I hadn't

Thank you both - I hadn't realised that the teeth didn't develop until later, or that this was a juvenile... lots to learn on these. :-)

dejayM's picture

wall snail

Those teeth are very hard to see anyway. From the pictures, I'd say Balea heydeni. Almost certainly not bidentata because of the angles at the mouth end.
Read this and see picture
....note barrelled appearance
Oh dear - why can't I get the ID panel to work for me!

Joe Botting's picture

Yet more options...

Thanks for that Derek... I confess I'm all at sea here. I think the problem is that it's juvenile, and therefore doesn't look quite like it's meant to... B. heydeni is clearly another to look at closely, though.

martinjohnbishop's picture

Do you have the specimen?

Identification is easier with the actual material rather than from photographs. You need to make a small reference collection of
adult and juvenile material of Clausilia and Balea. Size, shape and shell sculpture, including the embryonic whorl, is important in distinguishing species.

As stated above, I am sure this is Clausilia bidentata (a juvenile).
Whorls are too flat for Balea and sculpture is striate rather than wrinkled. Size is too large; if the height is 8mm the width is 2.3mm.

Balea heydeni is little different from B. perversa.
B. heydeni should be called B. sarsii according to Anderson

You should look for B. perversa on rocks and B. sarsii on trees.


Joe Botting's picture

Thanks again, Martin

No, no specimen - this isn't a group I've specialised in at all (as you can tell...). This is why these discussion are so useful - I now know roughly what I need to look for if/when I do try learning them properly. Will be sure to collect as many empties as a I can in future. :o)

stevegregory's picture

I agree with Martin

"I am sure this is Clausilia bidentata (a juvenile)"

dejayM's picture


I have spent an age looking for perversa in a crowded sarsii place. Separating them is REALLY not easy.
I have found this site the most useful, so far
but still, the differences are not easy to discern.
I am inspired by Chris Owen' post here and will, in due course, post up some similar pictures.
iSpot seems to auto 'correct' perversa to perverse!