Northwest Dive Club

I cannot decide what this is. Kathy and I examined it for several minutes and still have no idea. For the life of me, it looks like some kind of abalone. It's about 6" across, and though it's not visible in the photos, it had a raised foot, which is to say, the shell isn't flush with the piling it's on. I decided it can't be an abalone, because they don't live here, plus I didn't find the characteristic holes in the shell. But I am completely stumped as to what else it might be.

Bonus: if you zoom way in, there's a little bitty chiton living on it that's pretty much the same color as the pink encrusting stuff. I found that one by accident while processing the pix.

This was at Titlow, by the way.

Here they are. Help?

From the pics alone I'd guess Pododesmus (jingle shell) but 6" would be an awfully big one.
The other possibility would be a rock scallop that is just unusually smooth and symmetrical because it grew up on such a smooth surface. But I would expect that to be more round.

rock scallop was my first guess as well, but I didn't know if they would grow on a log

Greetings,

I'm also guessing rock scallop although it would make more sense if the shell conformed exactly (wrapped around, if you will) to the piling.
As to whether a rock scallop would settle on a piling - I don't think they put much thought into the process compared to some other sessile critters. At the Feiro Center we had one settle and grow on the wall of a Rubbermaid stock watering tank; it grew to about 5 inches in diameter before being dislodged due to the tank being more flexible than its shell. BTW: The scallop settled 7 or 8 years ago, was dislodged 3 or 4 years ago, and is still doing fine today. We also have a small one that has settled (in the last year or so) in the remains of a Piddock hole that's way too small to allow proper growth. We're looking forward to seeing how the animal deals with its self inflicted problem.

Adaptably yours,
Alex

P.S. We do have a local species of abalone - the Northern or Pinto Abalone (Haliotis kamtschatkana) but it has been so overfished that seeing one would be quite rare.

Hello again,

Just a quick follow-up.
I just looked at a number of pictures of Pinto Abalone and False Jingles and none of them seemed to show any sign of Yellow Boring Sponges (Cliona sp.); these sponges are often associated with Rock Scallops and are very much in evidence in the pictures shown above.
FWIW: This is ABSOLUTELY NOT definitive.

Speculatively yours,
Alex

But isn't the rock scallop a bivalve? I don't think this one is. Feel free to correct me, as several of my critter books seem to have gone into hiding.

dwashbur wrote:But isn't the rock scallop a bivalve? I don't think this one is. Feel free to correct me, as several of my critter books seem to have gone into hiding.

A bivalve that has one side glued and conforming to whatever it has grown on.

Well, definitely not a Northern/Pinto Ab. No foot/mantle, no respiratory holes, nothing. So to answer your original question, no, it couldn't be.

As for Rock Scallop - that makes the most sense, given the mounded shape, size, and the stuff growing on it (yellow boring sponge is real typical growing on Rock Scallops).

But weird you didn't notice the orange 'smile' before it clamped down? Because it looks pretty clamped down solid right now!

- Janna

Janna, we didn't see any motion at all. That's part of the reason it didn't look like a bivalve. Gonna have to go back and take yet another look. Aw, shucks