Basically everything is correct. You marked the siphon a bit too long, it just very little spans within the mantle cavity itself.  What you called the mantle skirt is usually called the mantle edge.

Dear Frank, 1 is mantle edge or border, and the free tip of the region that you mark with 2 is the siphon. Maybe internally, there are shallow folds that lead from the siphon to the osphradium and therefore you identify all as a single structure (siphon). But the siphon itself is only that part of the mantle edge to the left of the body that projects further forwards and accomodates inside the siphon canal of the shell. The remaining structures are also correctly identified. To the last, may I ask you from which locality and when did you collect this specimen and how was the shell? I'm just curios about it because here in Northern Spain we have a few shell morphs. Best wishes

Ian: I agree with the colleagues. Also the albumen gland is besides the ingesting gland (to the rigth).

Dear Yu, Alexandra and Gregorio, thank you very much for taking the time to answer my question, and for correcting my misconceptions of the terms 'mantle skirt' and 'siphon'. Best wishes

Ian

Alexandra, the specimens (the one above and the male in my other message) are from New Brighton at the mouth of the Mersey Estuary, near Liverpool, England, July 2014. The animal above is from the first attached image below, shell height 33.9mm. The male in my other message is from the shell in the lower image below, shell height 30.6mm. Both had many barnacles on them which I removed for the photographs. The species is rare in Liverpool Bay. The only ones I have found in Liverpool Bay are on a single breakwater of concrete blocks at New Brighton and on a small rocky island in the Dee Estuary 13km to the west. The account I am preparing will have images of many morphs found between the south coast of England and the Orkney Islands (north Scotland).

Best wishes, Ian

Nice! Thanks al lot for the beautiful images and information. I will also try to make pictures from the N. lapillus morphs that we have here. They are neither abundant here. I've found them in four sites in Asturias, Bañugues, Colunga, Gijón and Tapia de Casariego in rather exposed rocky shores always close to the sea anemone A. equina and small mussles. Stramonita haemastoma are locally much more abundant. We have those morphs that appear in your pictures but also others much more slender and darker. Here I've seen spawn masses in spring this year. Do you know when they breed there?

By the way, are you preparing a kind of anatomical virtual catalogue of marine snails? Let me know, I've plenty of sketeches and pictures and I don't know yet if I ever will publish them.

Dear Frank,

Everything is correct only the mantle skirt which usually called the mantle edge. I am working with Hexaplex trunculus and Bolinus brandaris and they have the same anatomy as Nucella lapillus.

Best regards.

Dear All

Here is a live female displaying her translucent upper body. The features that I think can be discerned are:

1-1: ‘S’ curved retracted proboscis with pink buccal mass within its anterior, 2: yellow-brown gland of Leiblein (secretes digestive enzymes) and 3: opaque white salivary glands. 4: columellar muscle less translucent. Tentacles contracted. The features are some of those shown in  the opened mantle cavity I posted on my other question re male, but I've posted this here to keep male & female separate.

As the valve of Leiblein prevents the contents of the gland of L. from passing into the anterior of the proboscis, I assume the gland's digestive enzymes are for the "meat soup" when it has come down the proboscis. Am I right in thinking that the toxin and enzymes for exterior digestion come from the salivary glands. (I hope this makes some sense - I'm ready to be told I'm completely confused about it)

All advice will be gratefully received.

Cheers

Ian

3=acinous salivary gland

2=gland of Leiblein (I have seen in individuals from here dark red glands of Leiblein, but this must depend on the diet).

the 1 close to number 2, on my opinion is still gland of Leiblein, at least, I don't see any difference with the texture and colour of the gl. Leiblein.

4, I wouldn't call this properly the columellar muscle. But iI'm not sure about it.  

The gland of Leiblein is a kind of mixed organ that have secretions for digesting the "meat soup" but it also function like a kind of  kidney and has an absorptive and excretory function. It is irrigated with blood vessels and seem to accumulate heavy metals that are chelated with chelating agents. The enzymatic break down occur in the lumen of the gland but also intracellularly. I've on researchgate a poster on the ultrastrucutre o the gland of Leiblein. You may download it and get a few ideas about the function of the gland.

There is also a work published on the ultrastructure , histology and structure of gland of Leiblein of Nucella lapillus, but right now, I don't find its reference and don't remember the name of the authors.

There seem to be a relationship between the volumen of the valve of Leiblein and the gland of Leiblein, and in fact, the valve is there to avoid regurgitation of the "meat soup".

The salivary glands in Nucella lapillus are in fact two different pairs: one pair of tubular accessory salivary glands, which secrete a toxin for narcotizising preys, and a pair of acinous salivary glands, which secrete the digestive enzymes for the external predigestion of the prey.

Thank you Alexandra for all your help, both above and off-list. Your comments showed me that I had misunderstood the size and course of the proboscis, and have greatly added to my knowledge.

Best wishes

Ian

Thanks to all who helped. I have uploaded a pdf of my Nucella account at https://www.researchgate.net/publication/264934519_Nucella_lapillus_identification_and_biology?ev=prf_pub and it is also available on Flickr at https://www.flickr.com/photos/56388191@N08/sets/72157645946302058/ Any comments/ corrections will be welcome.

Cheers

Ian

Data Nucella lapillus, identification and biology.