Tuesday, September 09, 2014


A couple of years ago, faced with snail egg capsules and an infant snail found with them, I tentatively identified them (with help from commenters here) as one of the rock snails, aka murex snails or Muricidae. I thought they were probably Trophonopsis orpheus, or another of the trophons. These prey on barnacles or mussels and other bivalves, and seemed to match some barnacle-eaters I'd had previously in the aquarium.

The hatchling, only a few millimetres long.

There were problems with the id; some references called it a subtidal snail, living at depths up to 180 feet. But I had found these in the upper intertidal zone. In Marine Life of the Pacific Northwest, it was the only rock snail that matched the snails I found, but again, it was supposed to be subtidal.

So every time I find another of these, or mention them, I spend some time reviewing the websites and books, looking for a closer match, a snail that fits everything I'm seeing in my tank.

And now, having the egg cases at hand, and confirming that these snails do, in fact, lay these eggs, I think I've been mistaken; that they are no trophons, after all.

Look at these egg cases. (Copyrighted, so you'll have to go there to see them. Here's the page; scroll to the second species.)

Now look at these, from my tank.

Tillie's eggs. A good match.

These are from the Leafy Hornmouth, Ceratostoma foliatum. This is another Muricid (rock or murex snail) that lives in the intertidal zone, but almost all the photos I find are of the full-grown adults; in these, the ribs are prominent, "leafy". The younger ones are like those in my tank.

This is fairly common to find intertidally.  The juveniles exhibit crosshatch sculpturing.  The axial ribs grow to large flares as it matures.  The adults may be plain white to purplish and may be striped.  At the base of the aperture there is a projecting tooth.  It lays a distinctive egg case. (From PNWSC.)

The Wallawalla.edu page adds more details: the siphonal tube of the Leafy Hornmouth is closed along its length, opening again at the tip. And the foot is a mottled cream colour.

(The siphonal canal of Trophonopsis is open.)

This is the youngest one in my tank, still quite small. The siphonal canal is completely fused along its length. The tooth is only visible from this angle as a slightly whiter spot. The shell is white with purplish stripes.

Here's the tooth, looking from the side.

Tillie, laying her eggs. The siphonal canal is closed, the tooth is near the entrance to the canal, and the flesh is a mottled creamy colour.

Down at the beach this afternoon, just below the high tide line, I was turning over rocks, looking at flatworms and a variety of eggs and egg cases. On one stone, I found several clumps of freshly-laid egg cases to match the ones at home. And there were the snails; some laying eggs, some eating barnacles. I turned each one over. Every one had the closed siphonal canal and the tooth.

Snail on rock, stony section of upper intertidal zone, Boundary Bay.

One snail in my tank looks like these, (but cleaner) but is much smaller. And its siphonal canal is open. It has no tooth. It's the oddball. Or it's too young to have developed yet. We'll see.

But. There's always a but.

On the Wallawalla.edu page, I see this:
Depth Range:  Low intertidal zone and subtidal to 60 m.
Habitat:  Found on rocky faces near barnacles and bivalves.  Avoids sand and mud. Most common in areas of strong surf ...
So I'm still not totally convinced; maybe other snails have the same egg cases, the same tooth, and the closed canal. I want to see if Mike and Tillie and their companion develop those big leafy wings as they grow larger. I'll keep on studying the reference sites and books until then.

What do you think?

1 comment:

  1. What i think is that you're doing some truly fascinating studies of these snails! I agree with your line of thinking on the ID. It's good that you are studying the development of the snails and also comparing them to those that are active in their intertidal zone habitat. Your photographs are wonderful, Susannah!


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