The door to the moon?

  

The operculum, sometimes called a "trap door", to a Lewis's Moon Snail (Neverita lewisii).  This is the part attached to the snail's foot that seals the opening to the shell when the animal pulls in.  This operculum was 2¾ inches (7 cm) long.

Interestingly, the inside of the operculum was very reflective and looked quite silvery in the overcast light of the fog today (17 August 2024).

Who's the culprit?

  

This is a scene we came across after finishing field work this morning (9 May 2024).  Some empty-looking whelks (Nucella ostrina) on the sand...and upon closer inspection, their opercula nearby (the operculum is the "trap-door" on the bottom of a snail's foot that seals the opening to its shell when the snail is pulled in).

It looked like the snails had been eaten by a predator, but we couldn't recall seeing this before, so we looked around a little more.

We found even more evidence that something had been eating both whelks and limpets.  Here are a few examples, including snail shells and overturned limpet shells with most of the soft parts missing, but with a thin ring of tissue, evidence that they had been eaten recently:

 

 

So...who was responsible for eating these snails and limpets?

 

We weren't sure, but we kept looking, and Eric eventually spotted a clue.  Tracks in the sand around some of the predated shells:

 

 

 

After thinking through the possibilities, we're guessing these footprints might belong to a rat (!).

 

Rat predation on intertidal invertebrates has been documented previously (Thanks to Sergio!), but we don't recall seeing it locally before.  Maybe because there was a lot of sand at this site it was easier to notice the empty shells and the tracks in the sand.

 

Here's a close-up of one track in case anyone can help us with an identification.  The track was ~1 cm across.

 

 

 

You learn something new every day!

Red Turban

A wonderful Red Turban Snail (Pomaulax gibberosus), photographed in the rocky intertidal zone in northern Sonoma County on 25 February 2017.  This juvenile snail was only ~1 cm across.  (Adults can reach diameters of over 5 cm.)  Look for the distinctive nodules along the body whorl (photo above) and the spiral cords visible on the base of the shell (photo below).

Unlike many snails in this region, Red Turban Snails have a calcareous operculum ("trap-door").  And note that the operculum is very smooth:

 

P.S.  For a view of a different species with a calcareous operculum, review the Pheasant Snail post from 20 December 2015.

Calcareous

 

A pheasant snail (Eulithidium pulloides), grazing along a blade of surfgrass (Phyllospadix sp.).  I first showed pictures of the shells of these snails in April 2014, but I haven't shown the entire animal yet.  (They're hard to find because they're quite small — only a few millimeters long.)

One of the interesting characteristics of this species is its operculum (or "trapdoor").  In most marine snails, the operculum is made of a protein material (think about a moon snail operculum).  But in some species, including these pheasant snails, the operculum is harder and made of calcium carbonate.  

See below for a close-up of the white, calcareous operculum:

 

Can you think of reasons why it might be helpful for a snail to have a calcareous operculum?  (One possibility is mentioned at the bottom of this post.)

If you're interested in finding a pheasant snail, try searching the bases of surfgrass clumps during a good low tide.  

P.S. Calcified opercula are thought to be a defense against predators.