I work in ecological studies of benthic organisms in the Seine estuary (France). I am experimenting identification trouble with some specimens of Liocarcinus. Until now, with identification Keys given for English Channel, I balance between L. marmoreus and L. holsatus, but not with complete satisfaction. One of my main problems is that these specimens are often very small individuals, taken with Smith-McIntyre grab, so often very damaged. Recently I get bigger specimen form fish trawl in the same part of the Seine estuary (see picture above) and I now think that these individuals are L. vernalis. Could you please confirm us this identification and that this species has been recorded from the English Channel. Thank you for your attention.
Regards.
Yes this does look like it is L. vernalis and yes the species does occur in the English Channel. The acute second tooth of the carapace would indicate this more than L. marmoreus although all three species you mention can occur together. The occurrence of L. vernalis in this region has not long been recognised and so its true distribution is uncertain but there are several studies that document its presence in the UK, Belgium and the Netherlands as well as studies showing that its abundance in the Southern North Sea decreases in severe cold winters.
To my experience, L. vernalis has a longer merus on the fifth pereiopod. The teeth on the carpus of the cheliped excludes L. marmoreus. I would rather go for L. holsatus thought the middle tooth between the eyes on the carapax is generally a little more pronounced in that species.
http://flic.kr/p/eKkmRg
I think that the better tecniques for confirmation this identification is for molecular biology with COI gene and Barcode tecnoloogy
There are three possibilities: L. marmoreus, L. holsatus and L. vernalis. L. marmoreus can not be because the merus of the 5th pereiopod exceeds the merus proximal half of the 4th pereiopod. L. holsatus and L. vernalis can differentiate well the distribution of hairs dactylus of 3rd and 4th pereiopod. In L. vernalis hairs do not exceed half the length of dactylus, while in L. holsatus hairs greatly exceed the proximal half of the dactylus. Although the picture was not well appreciated this detail, it seems that L. vernalis.
Try contacting Pierre NOEL at the Museum of Natural History in Paris. One of the best French specialist taxonomists for decapods.
I agree with Javier, think of using barcodes (especially for the small ones). Based on our own library, all species can be identified easily.
Thank to everyone for your help! I'll check my other individuals...
Best regards
Always tricky to measure from photos, but the length/width ratio of the merus of P5 suggests L. holsatus, using d'Udekem d'Acoz & Rappé 1991 (Crustaceana 61). So I tend to agree with Hans Hillewaert, but Cédric d'Udekem d'Acoz, please convince me why this should be L. vernalis.
@ Victoriano Urgorri: do you have an ID-reference on the dactylus-hair range?
At the moment we are struggling with some Dutch specimens with intermediate characteristics, so response is much appreciated.
I have never seen specimens intermediate between L. holsatus and L. vernalis. On the other hand, I had sometimes problems for separating L. vernalis from L. marmoreus.
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