Hiatella arctica

Paula Lightfoot Hiatella arctica siphons?

Steve Wilkinson yeah - or you could have a debate about whether H. rugosa is a separate species or not: http://www.conchsoc.org/spAccount/hiatella-rugosa

David Kipling Oh great, another set of species that looks like sea squirts :). Guess we're going to need the "is it a bivalve or a solitary squirt in the silt?" theme to go alongside the ever-present 'sponge versus colonial squirt' issue. *sigh*

Becky Hitchin My first thought too ...

David Kipling At this rate a diver's guide to UK ascidians will mainly be sections on things that aren't squirts but look like it! I collected a bit of dead mans finger the other day (intertidal) ... Contracted when I touched it so not a sponge (first test passed). Error of my ways discovered when I left it the bucket of SW, where it promptly expanded the polyps!

Becky Hitchin There's a good title for a FB thread .. things that could be mistaken for a squirt ..

Claire Goodwin Or squirts that could be mistaken for other things - when I started out on sponges I got very excited by some weird star shaped spicules - turned out we'd collected an encrusting squirt.

Erling Svensen These tiny (1 cm long) mussels, may it be the Mytilus edulis - juvenil one?

Steve Wilkinson And looks like Irus irus over on the right (pinky siphons)

Erling Svensen I do think the one over to the right is Hiatella arctica - "stoneboringmussel" in Norwegian.

Erling Svensen There is also one in the centre of the picture.

David Kipling So Becky Hitchin, what do you think these red siphons in holes are? Look at the rest of the album for the scale and habitat geography. These squirts are all over the place, in holes (I assumed not made by them!), and will squirt out water a good 10 inches when disturbed. This is an exposed tidal headland on the N coast of the Bristol channel.

Becky Hitchin 10 inches? How very impressive :)

David Kipling A lot of them are on vertical rock faces, hidden in small holes in the rock. As your shadow passes they get spooked and squirt. Can be quite annoying when you're trying to look closely at something and you get a sudden squirt of warm sea water in your ear!

Becky Hitchin Dendrodoa or Distomus? Can't really tell what the siphon ends look like

David Kipling Distomus is more colonial - common test and they bud. Wouldn't have thought that fitted with this one-hole, one squirt pattern. Feels much more like proper solitaries that have settled in each hole and Dendrodoa was the one on my mind.

Becky Hitchin Was just sort of wondering whether they could be connecting under the surface somehow, but, yes, I think I'd go for Dendrodoa too

David Kipling These are holes in hard rock that has been weathered. I don't think it is honeycomb with connections between the holes although I've never actually prodded ...

Paula Lightfoot It's not only squirts that squirt! Boring bivalves squirt too when disturbed, and they extend their siphons during periods of exposure, and they respond to changes in light intensity. Did you get one out of its hole to make sure it's definitely a squirt?

David Kipling Not sure at all! There were Dendrodoa on some surfaces but looked different (look in the album) and you're right, I would have expected them to retract into being a blob rather than having extended siphons. It might also address a niggling question I've had, which is what is actually making these holes in the rock. If it's a bivalve that's doing the boring then that's two birds with one stone. I didn't sample any - it was purely a camera-based jaunt at low tide - but I might take the Spencer Wells with me next time and see what happens. What sort of species have red siphons and bore, Paula?

Paula Lightfoot Hiatella arctica, I guess that's why they're also called 'red nose' as well as wrinkled rock borer. According to Paul Chambers British Seashells, Hiatella arctica don't actually bore their own holes, they inhabit the holes made by other molluscs such as piddocks.

David Kipling I didn't see much by way of piddocks at that site, and MarLin suggests they can bore as well as nestle. OK tweezers and toffee hammer at next low water it is! Thanks Paula.

Becky Hitchin Piddocks squirt a few foot into the water when particularly aggrieved

David Kipling When is the next low tide at Worms Head Sarah ?