Looking for limpets

 

Leather Limpet (Onchidella borealis), crawling across the rock in the mid-intertidal zone on 24 July 2017.

Although this Leather Limpet stands out against the rock, sometimes they're well camouflaged against the background.  How many individuals can you find in the image below?  (Hint: They might be different colors and different sizes.)

 

I've circled the Leather Limpets in the next photo:

 

To learn more about Leather Limpets, and to see fun pictures of juveniles, check out the post called "What's it like on the outside?" from 25 August 2012.

P.S.  Leather Limpets seem to like foggy days, so this can be a good time of year to look for them!

    

Out for a stroll

A couple of weeks ago, Eric spotted this Reticulate Button Snail (Trimusculus reticulatus) out for a stroll.  Note the circular shell and the network of radiating lines.

 

We were very surprised for a number of reasons. These marine pulmonate snails are found in crevices and shaded overhangs in the rocky intertidal zone.  They're often in gregarious clusters (see next image), and are known to be relatively sessile (i.e., they don't move very much).

 

In our experience it was unusual to encounter a single individual, especially one that was out walking around!  In fact, we'd never seen the oral lobes extending in front of the shell before.  The lobes are an unusual shape (unlike the true tentacles of other snails), so we took some time to study them and to wonder about how they would be used.

 

I haven't been able to find anything about how the lobes might function at low tide.  At high tide the snail uses them for feeding.  Reticulate Button Snails are filter-feeders.  They produce mucous nets that collect phytoplankton from the water and then gather the nets with their oral lobes.

A few years ago I was also surprised when I encountered a very large aggregation of this species depositing eggs.  When I looked closely I noticed many egg masses adjacent to the shells.  (Note that often the reticulate pattern for which the species is named is eroded or overgrown.)

 

Intertidal Invertebrates of California says, "The eggs masses are gelatinous and petal-like, and are attached in rosettes on the rock around the animal that laid them.  Egg deposition occurs in April at Tomales Head [sic]..."

I took these pictures in July on Bodega Head:

 

You'll probably notice that some of the egg masses are white and others are brown.  I'm not sure what's going on with the colors, but am wondering if the brown masses are older?

 

Back to the animal we saw in late April.  It's hard not to wonder about its story.  Will it find an aggregation to join, or will it start one of its own?

 

What's it like on the outside?

While doing field work on the Mendocino coast earlier this week, Eric encountered a large concentration of egg capsules on the underside of a plastic washer that had been in a mussel bed (see below).

 

The white eggs capsules were deposited by a Leather Limpet (Onchidella borealis).    There's one adult Leather Limpet in the upper left corner of the photo.  [The yellow capsules are flatworm eggs.]

Leather Limpets aren't true limpets (they're pulmonates), but they look like limpets without shells.  Adults are ~6-10 mm long and live in the mid-high intertidal zone near algal holdfasts and shaded crevices.  Adult coloration is highly variable.  Many are yellowish-green, but others are whitish and some are deep maroon.  They graze on diatoms and microalgae.

 

 

In the photo above, there are two Leather Limpets (one red, one white), along with one true limpet (lower right) and one chiton (upper right). 

A few years ago, Eric found some Leather Limpet egg capsules in various stages of development.  We took some photos under a microscope.

Leather Limpets are direct developers.  The larvae complete their development within the capsule over ~30-40 days and then emerge as tiny juveniles ~1 mm long.

The capsules look a bit like bubbles.  Note that each larva is developing within an individual chamber.

 

This is a late stage larva.

 

  

A juvenile is hatching and crawling over the outside of the capsules.

 

 

 

This next picture always makes me laugh.  I can't help wondering if the juvenile inside (not yet hatched, but with two dark eye spots) is looking at the crawling juvenile and wondering what it's like on the outside.

The subtidal pulmonate

 

Okay, here's a species that I don't know much about, but am too intrigued by not to share.

This is Williamia peltoides, a marine pulmonate.  Most pulmonates are air-breathers (e.g., land snails and slugs), but Williamia lives in the subtidal zone.  I've occasionally found Williamia shells washed up on the beach, but this year I've encountered a few live individuals.

They look very similar to limpets, and are in a family that is sometimes referred to as "false limpets."  The photo above shows their limpet-like shape.  Note the pretty purple-red coloration with radiating white stripes.

They crawl on very large foot (see next photo).

 

In the photo above, you can also see a few interesting features.  Note that they don't really have obvious tentacles (as do true limpets).  Instead, they have rounded tentacular lobes.  I believe that little black spot surrounded by white on the right side of the head is an eye.

Behind the head, on the right side, you'll notice two other mysterious structures (see close-up below).

 

The leftmost structure with several layers or lamellae (that makes it look corrugated) is a gill-like organ.  It's not a true gill, and this feature separates them from true limpets (and is even unusual for pulmonates).  The rightmost structure is rounded and flap-like.  From what I can determine, this is an anal lobe and contains the anal opening.  The undulating purple feature (with white spots) is the side of the foot.

A couple of other interesting notes about Williamia: They have a thin periostracum (a chitinous layer covering the shell) that often extends beyond the edge of the shell (unfortunately, it's not visible in these photos).  And they release a white mucous when disturbed to deter predators.  [Trimusculus, another marine pulmonate on Bodega Head, also releases toxic mucous that can paralyze sea star tubefeet!]

 

Williamia peltoides on Bodega Head, 7 July 2012.