Friday, January 12, 2018

Chiton lips

"Woody", the green and blue chiton in my aquarium, spends most of his time plastered to a shell, a slow-moving, flattish, 2-inch-long mound blending into the background. If he has a "face", it's hidden. But for a moment, the other day, I caught him lifting the edge of his girdle, tasting the water.

Underside of the girdle, and the mouth, open. Also present: an amphipod, a mud snail, and a pink-tipped green anemone.

Woody does not have a head, as we understand the term. He has no eyes, tentacles, or brain here, just the mouth. (His shell does include light-sensitive spots, but around his mouth, there is no need, since it is usually clamped tight against the substrate.)

Like many other molluscs, chitons feed with a thin strap bearing rows of teeth known as the radula. The anterior rows are used up and discarded or swallowed and replaced by new rows moving forward like a conveyor belt. ... The chiton radula is noteworthy because one pair of cusps in each row is hardened with magnetite, which provides these teeth with a coating harder than stainless steel. They are the only molluscs that have magnetite-coated teeth. In fact, they are the only organisms known to manufacture such vast quantities of magnetite. (

Before I start to take photos through the glass, I scrub the inside walls; overnight, they develop a coating of green algae. A soft cloth removes most of it, but underneath that, there's always a more tenacious growth of yellowish-brown algae; for that, I use a green kitchen scouring pad, scrubbing and wiping with the cloth alternately. With a fingernail, I pry off harder lumps.

And even then, once I give up, the glass is still covered with these tiny pink dots, visible against the yellow flesh of the chiton. Pacific rose seaweed, trying to establish itself on every surface in the aquarium. When it grows on a shell, I can't rip or scrape it all off; it's tremendously tenacious. I tear off and discard double handfuls every time I clean the tank, but the glued-on "roots" are always left behind, ready to leap into action.

So fragile-looking, so delicate! And so strong!


  1. A friend was yesterday asking if it would be possible to keep molluscs used to a tidal environment (like limpets and barnacles) in a tank. I assumed not but wonder if you could advise?

  2. All my tank residents are from an intertidal zone; some of them have been in this tank for years. A few things are important, though. They need more thorough changes of water than fish do; a 20% change monthly is recommended for fish, but I change 50% of the water at the very least every two weeks. They need good water circulation, and regular changes of filter components.

    Being intertidal critters, they are more accepting of temperature and salinity changes, but they need to be regularly returned to their ideal levels. And they don't mind being removed from the water entirely in order to clean their tank. Do that with fish! (Don't.)

    My tank includes barnacles (two species), snails (several species), the chiton, assorted limpets. I have had mussels and clams, bubble-shells and sea slugs. They don't do so well, but not because they're intertidal, but because in a small tank, they're vulnerable to predators like the crabs, the anemones, and the carnivorous snails. So are the barnacles, but right now, with only two barnacle-eaters in the tank, the barnacle population is actually increasing.


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