Following the line of the limestone cliffs towards Kitchen Corner as the tide receded, the tide pools and beach were littered with dozens of living Rayed Trough Shells (Mactra stultorum Linnaeus) as they popped up to the surface of the sand. I don’t quite know why they chose to do this but it afforded an opportunity to see the living animal as opposed to the dead ones and empty shells that wash up more frequently on Rhossili Beach.
Two pale fleshy tubes joined together were extended between the two hinged shell valves. One inhalent siphon for sucking water with suspended nutrients inwards, and one exhalent siphon for dispelling de-oxygenated water with bodily waste products. I was afraid that these bivalved molluscs would die while gaping and exposed to the air, so I picked up a few and put them in the water of the pools but they were not very lively and did not re-bury themselves. I was surprised that no-one else seemed to notice them. Even the dog that I saw appeared more interested in splashing in the pools than snacking on the free harvest.
7 Replies to “More Rayed Trough Shells at Rhossili”
Why are they called Rayed Trough Shells – I can use my imagination but I don’t think I’d get it right.
A rare sight Jessica – well spotted. Not much escapes your keen eye!
I’m not certain about the “trough” bit but the word itself applies to a narrow, open, box-like vessel which might refer to the shape of the shell. “Trough” also also describes a ditch, trench, channel, furrow, groove, gully, or depression, so it’s use in the name of the group Mactridae (Trough Shells) may be an allusion to its burrowing habit.
The “rayed” part of the name is more straightforward. The outer surface of most shells of this species is characterised by differently-coloured radiating lines fanning out from the umbone (hinge-end) part of the shell – like rays of sunshine.
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It was odd that the molluscs “chose” to come out of their burrows at apparently just the wrong moment when the tide was actually going out. I could have understood it if the tide was just about to return and cover them.
Thanks Jessica, my imagination wasn’t so far off the mark then. Great photos as always 😄
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I agree great photos, did the siphons quickly retract when you approached? seems very odd to see them all on the surface so exposed.
Thanks for the post
Thanks for the comments, Coleshed. No, they did not retract their siphons at all or rebury themselves. Doomed to an untimely death en masse. Perhaps some kind of virus?