Atelecyclus rotundatus

Rob Durrant These pics show two specimens of what I recorded as Atelecyclus rotundatus, both kept in my aquarium some months ago. Apart from the colouration, they have many characteristics seen also in the specimen of my recent query, notably the similarity of carapace shape more to C. pagurus than to C. maenas. They don't seem to be as circular as mine recent one. And the legs seem longer and less hairy. But the antennae again are quite long. Most notably, however, the chelipeds clearly show lines of tubercles on the propodus. This characterises Atelecyclus, and I'm pretty sure is not found in C. pagurus or C. maenas. But is it diagnostic?

Rob Durrant Missed this one.

Rob Durrant Please explain the lines of tubercles on the propodus, Cédric. I can find no reference to these in descriptions of C. pagurus or see them in C. pagurus images.

Rob Durrant Really struggling to ID this little chap, only about 6mm across, found under a stone in water lower shore on a low tide at Hannafore, Looe. No doubt obvious to the more experienced! Help, please?

Rob Durrant I agree that the colouration is is often found in C. maenas, Dawn; but I didn't think so. It seemed too round, almost like C. pagurus, as were the teeth on the antero-lateral margins, not sharp enough for Shre crab. Also more hairy.

Rob Durrant Also eyes v wide apart, and seems to be 5 lobes between the eyes rather than 3.

Rob Durrant Definitely not a Hairy Crab. I know them very well, and have kept them in aquarium and have cast netting. As also Circular Crab.

Rob Durrant Chelipeds seem quite small.

Rob Durrant And now if I enlarge the upside-down image, I see the chelipeds are dark-tipped (not black), and do have lines of small tubercles like Atelecyclus rotundatus.

Andy Horton https://www.google.co.uk/search?q=Atelecyclus+undecimdentatus&rls=com.microsoft:en-US:%7Breferrer:source?%7D&rlz=1I7ADRA_en&tbm=isch&tbo=u&source=univ&sa=X&ei=rlN9Ur-BEo2QhQfcroHgAw&ved=0CEEQsAQ&biw=1024&bih=610

Andy Horton Circular Crabs have been found in shallow water over sand on Sussex shores. I have found them but not very often.

Rob Durrant Thanks, Andy. I have been looking again at the netting of a specimen I had covering three moults. and I think now that a Circular Crab is prob best fit at the moment. The pie-crust antero-lateral teeth, tubercules on dark-tipped chelipeds, hairiness, and 5 lobes between the eyes, all seem to fit.Will try to photgraph the netting tomorrow for comparison, and see what you think. I do resist the shore Crab suggestion, though. A lot there doesn't seem right to me.

Marco Faasse Rob Durrant, you wrote "almost like C. pagurus". In my opinion you can leave out the two first words ... Its juveniles are less oval, more circular, and more hairy, with teeth that are more pronounced.

Rob Durrant Thanks, Marco, but I totally disagree. We have vast numbers of C. pagurus on my local shore, and I only ever see what are clearly identifiable as miniatures of the adults. But will post more pics of specific features.

Andy Horton I think it is almost certainly Carcinus maenas, the Shore Crab, as I assume they are all the same crab.

Rob Durrant They are all the same crab, Andy.

Andy Horton Where was it found? (Circular Crabs also come across as round.)

Marco Faasse It is either Cancer or Atelecyclus. On the last page of this publication you can find drawings of juvenile Cancer with roundish carapace, relatively long antennae and 5 teeth between the eyes (however they change quickly when they grow larger): http://core.kmi.open.ac.uk/display/4503180

Rob Durrant It was upside down on the underside of a stone in water on the lower shoree on a low tide, Hannafore, near Looe, Cornwall.

Rob Durrant Very many thanks for that very helpfulresource, Marco. I've had a look at those pages and saved the paper for a better look later on. For me, now, it's Atelecyclus. Not unusual for it be difficult to securely ID juveniles in many species, I suppose, since they are often somewhat 'fluid' perhaps.

Marco Faasse Also be aware that Atelecyclus undecimdentatus that is known from the Channel is more shaped like Cancer than A. rotundatus. I don't know whether the ridges on the chelipeds are diagnostic.

Rob Durrant Thanks, Marco.

Rob Durrant Very little seems to be available online by way of images, but the shape certainly fits better, and the tubercles are there.

Gerard Heerebout Agree.