Saturday, August 28, 2010

Full tank

Every day, we spend some time staring into my tank of intertidal critters, watching their doings, marvelling at their antics. And I haven't been posting about it here. I must remedy that; here are some of the fairly recent photos.

Cookie, the smallest crab. She grew up from a tiny thing, barely visible, and is now almost an inch across. Here, she's sitting still in the sea lettuce, getting ready to molt.

I watched her yesterday, grooming herself. As usual, she picked at invisible bits of stuff on her legs, wiped her mouthparts, scraped her pincers. And then -- imagine this -- one of those big pincers grabbed her eyestalk and yanked at it. She scratched away at the eyeball itself, vigorously. I was wincing, just watching her. She finished and went back to cleaning her legs, perfectly contented.

A Japanese nassa. There are a half-dozen or so of these; they wander around constantly, apparently ignoring the crabs and hermits that walk over them. Nothing seems to eat them.

Spot, a medium-sized grainy hand hermit. I like the pattern on the shell he has chosen; it's covered with barnacle scars, giving it a polka-dot look.

This is the backside of the largest hermit, "Barney"; you can just barely see one of his red antennae at the lip. When I brought him home, the barnacle was alive and feeding. Other hermits, the small, fast hairy hermits, ride on his shell often. Whether it was them or the snails that also hitch a ride that ate the barnacle, I am not sure. Now that the shell is empty, it has been taken over by a small green worm, just visible at the bottom of the barnacle. Occasionally, it stands up and waves around in the water, searching for food.

The largest of the anemones, about an inch and a half long.

These are some sort of a sponge, encrusting sea lettuce. (Update: now identified as Violet Tunicate, Botrylloides violaceus.) Each separate opening (look closely) is like the top of a little, pot-bellied barrel. Almost every one seems to be attached to the next, marching around and around in orderly lines. The pattern is more apparent in this next one:

Some of these are pink, some deep red, a few white.

These were very tiny, and almost completely transparent when they came home with me in some seaweed. They've grown; three are still transparent, but this one, the biggest at half an inch, is developing a pattern. I think it is a coonstripe shrimp. If so, they could grow up to 6 inches long in the wild, not so much here.

They drift around, seemingly without effort, even going against the current. Nothing bothers them; they even sit on the crabs' backs without getting grabbed at.

Two of the hermits watch a big flatworm engulfing a snail. This I had to see to believe. The flatworm oozes over the snail, and squirms around, trying to detach it from the glass surface. The snail holds tight; as long as the lip is on the glass, the flatworm can't get in to kill it.

The worm backs off:

... and tries again. This snail is ridged with jagged "wings"; it took several hours of persistent tugging for the flatworm to win out, probably with some cost to its "skin". We watched, off and on. So did the hermits. (The flatworm doesn't attack them, but were they worried?) Eventually, when I came back to check, there was no sign of either flatworm or snail.

Two days later, I saw the flatworm with a snail again, this time a smoother Batillaria. And the battle was taking place on the sand; the worm was having no problem wrapping itself around the snail. While I watched, with the snail completely overpowered, the flatworm started flowing away, dragging the snail down into the sand with it.

I've begun to bring home snails, mostly the invasive Batillaria, to feed the flatworms. There are two big ones, several tiny ones, all of them hungry.

One more critter. This one is tiny. The fresh seawater I brought home for the tank was silty; I let it settle out before I used the water. About an 8th of an inch of sand remained. Before I dumped it, I took another look. Something moved; something I couldn't exactly see; I just had the impression of movement. I got the lens and looked. Yes, something was moving, in one spot. Not a copepod.

I looked at it through the microscope. Wow! This was something I'd seen in the Encyclopedia and thought, "How strange!" I didn't expect to get to see it.

Look at the centre of the photo. Do you see a dark circle? Look closely. Do you see a pinkish thread coming out of the circle on the right? There are two; one to the left, almost invisible.

What I saw.

It's a worm, possibly a jointed three-section tubeworm, Spiochetopterus costarum. We see these on the tide flats at Boundary Bay, sticking up about an inch above the mud. The two tentacles, of course, are never visible at low tide, just a whole bunch of little matchstick tubes. There's a good photo of a feeding worm, here.*

The two tentacles wave to and fro; I saw bits of stuff touch them, get caught, then slide down the tentacle into the tube mouth. Sometimes the tentacles themselves are retracted, probably to be cleaned off; then they extend into the water again and go back to waving about.

*That's a good site for marine life; here's the index page.


  1. Wow, your photos are amazing, and the commentary is fascinating. Thanks for sharing.

  2. I actually have a full 30 gallon reef and I currently have about 6 of those little 2 tentacled worms under a certain rock that filterfeed. I have been searching all over the internet to find that lol. The tentacles are around 2 inches long now and the tube about 1 inchlong along the substrate. Mine however are a white-transparent color rather than pink.

  3. Hi, kdh... I have a later video of one of these, feeding. Here.

    And another video, with better visibility, but no food, on YouTube, here.


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