Sea shell identification please.

Over the last couple of days, some unusual shells have appeared on the
strand line on Praa Sands beach in west Cornwall, that I can't
identify from any of our shell books.

Very superficially, they resemble common flat-sided periwinkles
(Littorina littoralis). They vary in size from 1 to 2 cm in diameter,
so generally a bit larger than periwinkles, IME. In colour, the sides
are bluish-white, while the back (keel?) has a lavender-blue or
purplish stripe along its length. The opening is quite large and
slightly flared on the underside.

As found, an obvious feature is a transparent colourless multicelled
'sac' that protrudes from the opening. With the larger shells this is
perhaps 1.5 cm long, but correspondingly smaller for the smaller
shells. Whether this feature is an egg-sac (similar to the egg-mass of
the common whelk, but smaller, more transparent and more regularly
arranged), or a float-sac, I have no idea, but most of the shells I
found had it. The shells didn't seem to have an operculum, but I might
have missed it.

The soft parts are black or very dark brown in colour, and bleed a
purple dye when damaged. But I gather that quite a number of molluscs
are sources of purple die and this was used for dying cloth in ancient
times, so that may not be much help.

This may not be much help either, but in the strand line I also found
a horse-eye bean (Mucuna sp., probably M. sloanei), suggesting that at
least some of the drift had come from tropical America. The winds over
the last two weeks have been quite strong, anywhere from southerly to
westerly, and a couple of weeks ago we had a lot of 'By-the-wind
sailors' (Velella velella) washed ashore, although nothing like as
many as in 2004.

Has anyone any suggestions as to what the shells might be?

--
Chris

E-mail: christopher[dot]hogg[at]virgin[dot]net

On Mon, 18 Dec 2006 20:52:07 +0000, Chris Hogg <me@privacy.net> wrote:

By chance I have turned up the answer, when reading an item on
By-the-Wind Sailors. They're almost certainly Violet Sea Snails
(Janthina janthina), a pelagic species that float around on the ocean
surface (hence the air-sac) and feed on By-the-Wind Sailors, amongst
other things, and which have also been turning up on the beach in
variable numbers over the last two weeks. The sea snails are recorded
in ones and twos from time to time on westerly coasts in the UK. I've
collected about 70 after a fairly careful search. They must have been
washed up over the weekend, because they're higher up the beach than
the current strand-line.

--
Chris

E-mail: christopher[dot]hogg[at]virgin[dot]net

	#1
Chris Hogg	Sea shell identification please. Over the last couple of days, some unusual shells have appeared on the strand line on Praa Sands beach in west Cornwall, that I can't identify from any of our shell books. Very superficially, they resemble common flat-sided periwinkles (Littorina littoralis). They vary in size from 1 to 2 cm in diameter, so generally a bit larger than periwinkles, IME. In colour, the sides are bluish-white, while the back (keel?) has a lavender-blue or purplish stripe along its length. The opening is quite large and slightly flared on the underside. As found, an obvious feature is a transparent colourless multicelled 'sac' that protrudes from the opening. With the larger shells this is perhaps 1.5 cm long, but correspondingly smaller for the smaller shells. Whether this feature is an egg-sac (similar to the egg-mass of the common whelk, but smaller, more transparent and more regularly arranged), or a float-sac, I have no idea, but most of the shells I found had it. The shells didn't seem to have an operculum, but I might have missed it. The soft parts are black or very dark brown in colour, and bleed a purple dye when damaged. But I gather that quite a number of molluscs are sources of purple die and this was used for dying cloth in ancient times, so that may not be much help. This may not be much help either, but in the strand line I also found a horse-eye bean (Mucuna sp., probably M. sloanei), suggesting that at least some of the drift had come from tropical America. The winds over the last two weeks have been quite strong, anywhere from southerly to westerly, and a couple of weeks ago we had a lot of 'By-the-wind sailors' (Velella velella) washed ashore, although nothing like as many as in 2004. Has anyone any suggestions as to what the shells might be? -- Chris E-mail: christopher[dot]hogg[at]virgin[dot]net

	#2
Chris Hogg	Re: Sea shell identification please. On Mon, 18 Dec 2006 20:52:07 +0000, Chris Hogg <me@privacy.net> wrote: By chance I have turned up the answer, when reading an item on By-the-Wind Sailors. They're almost certainly Violet Sea Snails (Janthina janthina), a pelagic species that float around on the ocean surface (hence the air-sac) and feed on By-the-Wind Sailors, amongst other things, and which have also been turning up on the beach in variable numbers over the last two weeks. The sea snails are recorded in ones and twos from time to time on westerly coasts in the UK. I've collected about 70 after a fairly careful search. They must have been washed up over the weekend, because they're higher up the beach than the current strand-line. -- Chris E-mail: christopher[dot]hogg[at]virgin[dot]net