It bit me!

And that was a good thing.

A couple of years ago, around this time of year, we were walking at the edge of the incoming tide at Boundary Bay, watching small, darting fish. I noticed some other animals, smaller than the fish, and much more active. They were dashing about in every direction, never stopping, always within the first few inches of the tide line.

I took the top off my collecting pill bottle and laid it on its side in the water and, wonder of wonders, a few critters swam in! I've tried many times to catch fish that way; almost impossible; they know it's a trap and stay out. Tiny shrimp, amphipods, even roaming worms, are equally cautious. Not these guys! Nothing scares them.

At home, I put them in a shallow container (this was two years ago) and tried to take photos. Here's where it got difficult. They never, ever, stopped dashing about. All my photos, even a video, were of speeding blurs.

I found and caught some again the other day. And this catch was a repeat. Except that I thought a faster camera might help. It didn't.

But when I removed enough of the water to trap a speeder in a drop, he surprised me by pushing his way through the water surface, climbing over the lip of my tray, and setting off to explore on dry ground. And it's much slower going that way. He even tired himself out!

Here he is, in the lid again, and all tired out from hiking.

Photos taken, I turned my attention to other things. I was moving a shell to the tank, when something bit me on the wrist. One of my speed demons. So tiny, (that lid is barely an inch across) but he delivered a painful bite that hurt for hours.

And that was good, because it gave me the clue I needed to identify these critters. They're Water-line isopods*, and unlike all other isopods I know of, they are extremely aggressive. In fact, according to Dave Ingram at Island Nature,

... if you stand motionless as the water washes over your feet you may soon be covered with nasty red bites!

From WallaWalla.edu: Very few crustaceans will actually bite you but this nasty little creature is definitely one of them.  Barefoot waders in an area with Excirolana will find that the animals quickly swim toward and swarm over bare feet, biting them so hard that blood will be flowing within moments.  Since the animals are so small the bites are tiny but painful like a pin prick, and the animals are often present in swarms of thousands.  Rapidly shuffling the feet reduces but does not eliminate the number of bites.

Now they tell me! I'm glad my current wading shoes are closed. And I won't be getting anything less protective in the future.

These isopods are scavengers that help to keep our beaches clean by eating any dead matter they can find. Thousands will swarm over a dead fish at the water's edge, and reduce it quickly to a skeleton.  They don't mind live meat, either, apparently.

*Once known as Cirolana kinkaidi, then Excirolana kinkaidi, aka Excirolana chiltoni.

One down, one to go. And a toe-biter.

I was wrong, I think. Yesterday's worm is not a worm at all, but a normal part of the limpet.

Not a polychaete. A gill.

Example # seventy-umpteen for my list, "Why I Love Blogging". There's always someone with better information, always something new to learn.

In the comments, yesterday, Neil Kelley suggested that the "worm" may actually be a gill. He supplied a link to a diagram I had not seen.

Ventral (underside) view of a true limpet, with part of the foot cut away to show the gill. (Ignore the two critters at the left.) (Marine Life Information Network, Fig. 18)

All true limpets have gills. (Wikipedia) They take different forms, sometimes forming a ring around the body, sometimes, as here, one pointed, feathery extension, which may at times be visible behind the foot.

Another anatomical diagram, this one from the top, so the gill extends to our right. Image from R. Fox, Lander University.

Other diagrams have not been as clear as these, usually showing the gill squished in alongside the other internal organs.

And I finally found a few photos of limpets with the gills showing. (It's amazing how knowing what to plug into Google turns up what you're looking for!) All of the photos are small, and mostly vague, but here's a clear one. The photo is for sale, so you'll have to click on the link.

Here's another:

Photo from Seashells of NSW.

So that's cleared up.

There's still that first worm to identify.

This one.

And a bonus: on Google+, Chris Mallory sent me a link to a page about another commensal scale worm in a limpet. The limpet is a keyhole limpet, quite distinct from the true limpets, but here's another instance of the benefit a limpet can receive from hosting a worm:

When Pisaster ochraceous* attacks Diodora aspera** in which this species is living, the worm moves around the pallial groove of the limpet to the side the seastar is attacking from, reaches out, and bites the tube feet or ambulacral area of the seastar.  This frequently results in the seastar withdrawing from its attack.

*A starfish
** The keyhole limpet