I am analysing faecal samples of waders from the mudflats of Guinea-Bissau and find small mudsnail shells that are extremely similar to the common Hydrobia ulvae that is found in European intertidal areas and at least as far south as Mauritania. However, I can't find any reference to the occurrence of this species further south.
Olá Pedro
I would be very surprised if Peringia ulvae lived near the equator as well as Northern Europe as it is intertidal and cannot change its depth to adjust its environmental temperature. Many mistakes are made in its identification; the scattered outlying records on GBIF may or may not be reliable. Even within Europe there are several spp. with similar shells that cause confusion.
The soft parts need careful examination for reliable identification. The cephalic tentacles are probably the most reliable feature as both shell and soft parts vary between individuals of P. ulvae (Many published descriptions describe only one of the variations).
You will find a set of images showing the variations at https://flic.kr/p/ekg7Qo and a detailed account below image one. Make sure to scroll down each page as every image has an explanatory caption. There is a link to Pennant’s original description(1812) in the references. He described it from the Dee estuary between Flintshire, North Wales and Cheshire, England. Most of my photographs are also from the Dee estuary.
Let me know if the links in the account do not work for you – there has been a problem with them on Flickr recently.
Best Wishes
Ian (Morddyn on Flickr)
Hi Ian,
Thank you for your reply. Unfortunately all I have are the shells obtained from bird faeces, so I can't look at the soft parts. Based on the shell I am pretty sure it will be a Hydrobia/Peringia sp. but I don't expect it will be possible to identify these shells to specific level.
Beside the question of whether they occur so far south, there is another thing that may indicate it will be a different species. In Europe and Mauritania most individuals I collected both alive and from bird diets are usually in the size range of 1,5-5 mm in length, while all the shells from Guinea-Bissau are below 1,5 mm in length.
This small size is probably the reason why we didn't find any live snails when we sampled benthic invertebrates. We were using a 1mm mesh, which is too large for snails of this size.
Hi Pedro
1.5mm does seem small. I hesitate to give further opinion as you have experience of P. ulvae in Europe; I hope you will excuse me if I'm too obvious. I find P. ulvae easy to see in shallow pools on bare muddy sand of the Dee estuary as it occurs commonly at densities of 8000/sq metre. It is much less common in muddy pools on the vegetated salt marshes near by. At 1.5mm your snail will be less easily seen, especially at low densities. Is it possible that the snails in the faeces on mud flats were ingested by the birds in a different nearby habitat?
Yes, I also see densities like that in Portugal, at the Tagus estuary where I do most of my work. As for Guinea-Bissau, it is hard to say, the birds don't seem to move a lot while foraging, so we believe they were feeding about the same places where we collected the faeces. But I was quite surprised to find them in the faeces, because we didn't find a single Hydrobia like snail in the field.
Hi Pedro,
I found Peringia along the coast of Morocco. For Guinea-Bissau check the WIWO reports or contact some of the Dutch guys, e. g. Leo Zwarts
Best
Michael
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