Sunday, July 12, 2009

Underwater kitten and wandering anemones

When is a crab like a kitten?

When you tempt it with a chopstick.

Let me explain: every day I tend to my salt-water beasties (now moved from the dishpan to a regular aquarium). I clean the filter, settle any seaweed that has come loose, and check to see if all the visible critters are alive. I keep a chopstick handy; with this, I gently tap any open clam or mussel; if they close, they're alive.

Yesterday, one of the clams had moved over beside a sand dollar shell tipped up against a rock. When the chopstick passed the gap underneath, something slashed out at it, much as a kitten under the bed attacks your toes. I waved the stick again; same result.

It turned out to be a crab. After a few attempts at the chopstick from shelter, he came out and tangled with it in the open, chasing it here and there, grabbing and pinching.

Laying in wait.

Later on, I watched him wander about, eating. He uses those pincers much like a knife and fork, and surprisingly quickly, picking up tiny morsels of food and bringing them to his mouth. The "jaws" chomp away, and the pincers go back for the next bite.

The two white strips (maxillipeds) at the mouth move like sideways lips and teeth.

It was interesting to watch him find a meal. For the appetizer, he scraped at the back of the clam, picking up invisible (to me) specks and eating them. (The clam ignored him, except when he got too near the lip. Then it closed down for a few seconds.)

Then the main dish: he moved out into the open and grabbed a piece of dead barnacle. This he broke in little pieces, chewed on them, and spit out the crumbs.

Occasionally, the current brought a fragment of seaweed past his face. He slashed out at these, the same way he had attacked my chopstick. When he caught one, he held it up to his mouth and chewed away.

Picking some salad greens.

And for dessert: more salad. He went to the back of the aquarium, where a forest of sea lettuce waved above him, raised the pincers and picked himself a few good-sized pieces. Yum!

On to the wandering anemones.

I had always thought that anemones were sessile: once they had settled onto a rock, they were there for life. I was mistaken.

Several of my anemones were anchored on pieces of kelp. With time, the kelp started to rot away.

Small brownish anemones on kelp. The edges are disintegrating.

Plumed anemone on disappearing kelp.

When the kelp was almost gone, the anemones moved to anything solid in the vicinity; the glass, a mussel, a rock. And moved again, and again. Almost every morning I find them in a different location.

White plumed anemone now on stone. Brown one on barnacle shell.

Another on a white stone.

And a baby white on another stone. Oregon pillbug (5 mm.) behind it, for size comparison.

Bonus: a small hermit crab, in an Amphissa shell.

Grainy-hand hermit, Pagurus granosimanus.



  1. Super interesting post. I had no idea that anemones could move. And I love the crab/kitten analogy. In the picture it does sorta of remind me of a kitten hiding under something waiting to pounce.

  2. I love the crab-kitten analogy, too. It makes the crab come alive with familiarity. Did not know what busy eaters they are. The anemone feel like children when you write about them. Nice to see the ocean world through your eyes.

  3. Thanks for posting your observations. I too never realized anemone movement until recently, watching a segment of a documentary showing the bottom-life in fast motion and to my surprise seeing the anemones scurry about. Maybe you can set your camera on a tripod and recurring timer (if available) to see how fast they really move?

  4. That's a good idea, Tim. I'll see what I can rig up.

    Vickie; The more I watch the small things, the more I realize how similar we are, how we are related.

    Bevson, thanks! I am beginning to think the crab is "playing" with me; today he followed my chopstick all around, poking at it.

  5. Your sea-kitten sounds charming.
    I did not know that anemones moved around either! Thanks for sharing.


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