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Littorina obtusata

(Linnaeus, 1758)

Cat Wilding These eggs were found on the rocky shore at Polzeath this weekend, does anyone have any idea what might have laid them?

David Kipling Size? And what are they laid on?

Cat Wilding about 3/4mm across, laid on saw wrack. A few nudibranch species found on the day

David Kipling Does look like mollusc eggs - what nudis did you see?

Cat Wilding Sea hare and another, have to check what it was.

Douglas Herdson Are they Flat periwinkle - Littorina obstusata/mariae/littoralis?

Cat Wilding aeolidia papillosa

Douglas Herdson Aeolida are larger pink and wavy.

Cat Wilding they are raised, like tinyturquoise donuts

Paula Lightfoot Lacuna vincta eggs?

Cliff Benson Hi Doug, Hope you are well have you had anything to do with I spot a BBC OU thing seems quite good fun!

Cat Wilding Oooh Paula Lightfoot, nice one, that looks bang on! Interestingly not currently listed by Marlin as having any records from the North Cornish coast... :)

Paula Lightfoot Interesting records then, well done! Did you see the adult snails as well or just eggs? http://www.conchsoc.org/spAccount/lacuna-vincta

Ian Smith My first inclination was, like Paula, to Lacuna vincta, but the colour made me look it up in Fretter & Graham, Brit. Prosobranch molluscs (1962). Firstly, Littorina obtusata/mariae spawn is not doughnut shape; it is kidney shape or circular. The latter shape is sometimes confused with spawn of Lacuna pallidula (inverted watch glass shape). F&G say of Lacuna vincta spawn "It forms the familiar yellow rings which may be found from Jan. to early summer on various weeds; Lebour stated that other egg masses of similar shape which are pink or green almost certainly belong to another species." F&G said that the spawn of other British Lacuna spp. had not been described. Maybe Cat's is one of them. But difficult to rear to find out as they hatch as veliger larvae that live in the plankton. Or Lebour might be mistaken.

Cynthia D. Trowbridge Certainly look like Lacuna to me :-)

Message posted on Seasearch Identifications on 04 Mar 2013
Paula Lightfoot Thank you very much for your comments on my Onoba photos! I also have a question about these periwinkles - is the smaller, darker one Littorina mariae and the larger one on the right is L. obtusata?

Ian Smith Hi Paula Much depends on the exposure of the shore and shore zone/algae they are found on as there are very distinct ecotypes. The fullest info is in an expensive Ray Society monograph on Littorina by David Reid of the Natural History Museum (BM). A free pdf is at http://www.field-studies-council.org/fieldstudies/documents/vol7.3_202.pdf but it is mainly from a study on the sheltered Menai Strait and has been overtaken by Reid (L. mariae is now L. fabalis). I'm going to duck naming your two shells; maybe Jan will be braver:-)

Ian Smith second thoughts; both L.obtusata. One on left has typical flare downwards of aperture found on immatures. One on right has wide open unrestricted aperture of obtusata.

Dave Rolfe Left one also has developed aperture of an adult fabalis, I would say fabalis on the left, obtusata on the right. To me it looks too big and well developed to be obtusata.

Jan Light I agree with Ian, both these specimens are Littorina obtusata.

Dave Rolfe Let us agree to differ, without the actual mollusc there is no absolute way of telling. I have the same problem with the L. saxatilis complex even though I have the book!

Message posted on British Marine Mollusca on 12 Mar 2013
Animalia (Kingdom)
  Mollusca (Phylum)
    Gastropoda (Class)
      Caenogastropoda (Subclass)
        Littorinimorpha (Order)
          Littorinoidea (Superfamily)
            Littorinidae (Family)
              Littorininae (Subfamily)
                Littorina (Genus)
                  Littorina obtusata (Species)
Associated Species