Am I right in thinking that the grey feature labelled 5 in the attached image of Tonicella rubra is probably a pallial afferent blood vessel/ sinus/ vein taking blood to the ctenidia? If so, which terms would you use to describe it?
I have been unable to find a labelled diagram of the feature in Jones & Baxter’s Linnean Synopsis, or Jardim & Simone http://www.scielo.br/scielo.php?pid=S0031-10492010004000001&script=sci_arttext#fig20_21 or in Schwabe http://verlag-pfeil.de/04biol/pdf/spix33_2_02.pdf . Can anyone direct me to a free on-line source that has one?
Other numbered features I think are:
1: hypnotum spread wide to grip substrate; coated with colourless granules, some stained by detritus.
2: mantle lappet (posterior expansion of mantle fold) partly concealing ctenidia.
3: hypnotum moved far out to form channel at posterior for release of faecal pellets from adjacent anus, as well as exhalent water and sperm or ova.
4: foot spread widely to grip substrate; partly concealing pallial groove.
I'm not a molluscan specialist, but I'll take a shot at this. The item labeled 5 is a pallial blood vessel. I'm not sure if it's the afferent or efferent vessel. The other labels appear correct. Item 3, not sure you can say the hypnotum is "moved far out", maybe the term is flexed?
Dear Jeffrey
Many thanks for your very helpful answer confirming the feature as a blood vessel. The text of my account contains this:
“Circulation: blood travels from the head-sinus through a grey afferent blood-vessel in the mantle lining the pallial groove to the ctenidia (also through sinuses in foot and viscera). After oxygenation, the blood passes from the ctenidia to the adjacent heart located at the posterior of the animal and is pumped through a medial aorta to the head sinus.”
This is my simplified version, I hope accurately interpreted, of that on pp. 17 &18 in Kaas and Belle; extract at
https://books.google.co.uk/books?id=CKautf2EUPkC&pg=PA17&lpg=PA17&dq=chiton+circulation&source=bl&ots=ZLfJ_LSj1N&sig=Z_SbE62dM3-oBiZcA7UZHqj2uU8&hl=en&sa=X&ei=jbyaVIKOF9Sv7AaK4YGgDw&ved=0CCMQ6AEwAA#v=onepage&q=chiton%20circulation&f=false
As the ctenidia are adjacent to the pericardium the efferent blood from the gills has a very short route. To fit the circulation pattern do you agree that the grey vessel (5 in my image) will be afferent?
Re the posterior hypnotum, I have changed “pushed out” to “flexed” as you suggest.
Thanks again and best wishes
Ian
My limited understanding of chiton circulation in the gills is this: there are two vessels in each ctenidium, the efferent = away from heart, into the gill; and afferent = draining the gill, towards the heart. The large vessel that you show is likely a major afferent vessel draining the hemolymph from the ctenidia and moving it posteriorly toward the heart.
I'm not sure that "flexed" is correct, but perhaps it is. Common exhalant aperture is used in some figures.
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