Ready to settle down

  

Okay, back to these little snails that I posted on 27 January 2024!

This would have been a challenging one to identify unless you've spent some time looking at vermetid gastropods, or tube snails.  These are newly hatched Petaloconchus montereyensis!

And if you haven't heard of tube snails — yes, that's right, these are snails that don't crawl (at least as adults) and instead live in a calcareous tube that's cemented in place.  

This species of tube snail is a brooder — the adults lay egg capsules inside their tubes and the juveniles hatch and crawl away.  They only crawl for a brief time before attaching to the substrate — e.g., a rock surface or the tube of an adult.  (They tend to be gregarious.)

One of these snails settled after only two days.  In the video below you can see the tiny juvenile (only ~2 mm across) with the new tube that it produced.  And if you look very carefully you can see the coiled shell that it started out with at the very base of the tube!  So cool!  

As adults these snails are attached to the substrate, so they feed in a different way than many common marine snails.  Instead of grazing on algae on the rocks or in tidepools, Petaloconchus feeds by casting a mucous net into the water, letting organic material get caught in the net, then pulling the net back into its mouth.  The snail uses its radula (like a tongue with rows of sharp teeth) to retrieve the net.  Eric captured some video of that feeding motion, too, so he included it in this clip.  This is pretty spectacular footage of tube snails, so be sure to check it out!

The video sequence goes something like this:

• First 20 seconds — juveniles crawling on their own
• At ~22 seconds — juveniles exploring the outside of adult tube snails
  
• At ~48 seconds — close-ups of the newly settled juvenile with a coiled tube!
• At ~1:05 minutes — miscellaneous shots of adult tube snails with nice views of their radulas in action
  

Thanks for the terrific video, Eric!

Hauling in the net

 

A few years ago, I was excited to write about one of our local tube snails, Petaloconchus montereyensis.  (You can review that post from 11 June 2012).  

I mentioned that Petaloconchus produces mucus nets to capture food particles from the water.  Well, just last month, Eric caught some of their feeding behavior in a short video.

Before watching the video, it will be helpful to remember a few things:

Petaloconchus has two sets of tentacles: the cephalic tentacles are larger, darker, closer to the edge of the shell, and near their base, have a black spot, which is the eye.  The pedal tentacles are smaller, paler, and closer to the operculum (the round "trap-door").  Look for both types of tentacles in the photo below and in the video.  (The pedal tentacles help guide the mucus nets when feeding.)

 

To feed, Petaloconchus spreads a large mucus net into the water for capturing drifting particles.  Then they use their radula (tongue-like organ lined with rows of shiny teeth) to grasp the mucus net and haul it back into the mouth using a very rhythmic motion.  This is one of the behaviors highlighted in the video.

vermetid feeding sanford from Jackie Sones on Vimeo.

These tube snails are relatively small — the largest tube openings are ~2 mm across — so Eric filmed them under a microscope.  Otherwise, it wouldn't be easy to observe this behavior and to watch these fascinating snails in action.  Thanks, Eric!