Tiny shells and spines

Well, I'm running out of time tonight, but I thought it would be fun to share this photo:

 

While doing intertidal surveys this past weekend, we noticed quite a few Sandcastle Worm (Phragmatopoma californica) tubes that were built primarily out of Foraminifera (informally called "forams") shells and small sea urchin spines.  [Forams are single-celled amoeba-like protists.]

More often, these worm tubes are made of darker colored sand grains (see the post "A close call" for examples of the more typical tubes).  But the tubes we saw this weekend really stood out — beautiful white foram shells cemented together with green and purple urchin spines and skeleton pieces.

I'm not sure if the forams are more common right now for some reason, but the worms sure did a good job at finding them and using them to build their tubes!

Electric blue

I first posted about Sandcastle Worms (Phragmatopoma californica) on 8 January 2012.  They're amazing worms, and it's worth sharing a few more things about them.

After 8 years, we've noticed that the abundance of Sandcastle Worms on Bodega Head varies quite a bit among years.  Many were visible when we first moved here in 2005, but they've been relatively sparse during the years since then.  This, however, is a banner year for them.  In some places in the middle intertidal zone (near mussel beds), it's difficult to walk without stepping on a cluster of them.  Here are a few recent photos showing dense aggregations of their tubes.  (Most of the tube openings are ~5 mm across.)

 

Sandcastle Worms feed by extending a crown of purple tentacles into the water.  Outside of tidepools, the tentacles won't be visible unless it's high tide.  But in pools where the worms are submerged, you can see their beautiful tentacles.

 

I think the electric blue highlights are rows of cilia that are reflecting light at certain angles (see below).  The worms use the cilia to move captured particles (plankton, organic detritus, sand grains) towards the mouth.  Food is eaten, while sand grains are transferred to a special organ that adds liquid cement to bind the sand to the tube.

The operculum that seals the opening of the tube when the worm is withdrawn is made of fused setae (bristles).

Below is a close-up of a tube as seen under the microscope.  Note that along with sand grains and shell fragments, there are also quite a few forams, or foraminifera.  They're the very round, white, spherical shells with a nice chambered pattern (the forams are scattered across the tube, but see lower left corner for the clearest individual).  

 

Forams are amoeba-like protozoans with hard shells or tests.  There are over 200 species present in shallow coastal waters of California.  I haven't tried to identify this species, but if someone out there knows what it is (Tessa?), please let me know and I'll post its name.

Interestingly, I don't know if the worm attached the forams to its tube, or if the forams nestled into the wall of the tube on their own.

Sandcastle Worms

During a low tide this afternoon, I photographed a small cluster of Sandcastle Worms (Phragmatopoma californica) in the rocky intertidal zone.  In the first photo you can see two size classes -- this is a head-on view of the worm tube openings.  Sandcastle worms have free-swimming, planktonic larvae that settle gregariously.  I wonder if the two different sizes represent worms that settled in different years (e.g., larger in 2010, smaller in 2011), or if they just settled at different times within one year?

 

In this second photo notice the disc-like purplish black operculum (lower right) sealing the opening to the tube.  This is similar to the "trapdoor" of a snail -- a hard covering that protects the animal from desiccation at low tide.

And here is a photograph of a Sandcastle Worm larva taken under a microscope (the larva is ~1 mm long).  The anterior end (or the head end) is on the left.  Two bands of cilia (they look like short hairs) encircle the larva and are used for locomotion and feeding.  The long bristles (or setae) can be extended out to the sides and are used for defense.