Tidepooling at 66° North

During our first few days in Iceland, we were fortunate to find some excellent tidepooling locations.  We've been taking lots of photographs, but it's hard to find time at the end of the day to write a complete post , so I'm sharing a few fun highlights for now.

 

 

Silver-spotted Anemone (Aulactinia stella)

 

 

 

 

Northern Red Chiton (Boreochiton ruber) 

 

 

 

  

A small staurozoan (Haliclystis sp.).  This stalked jellyfish was very active so the image is a little blurry, but we were excited to find a couple of them! 

 

 

 

  

A striking Daisy Brittle Star (Ophiopholis aculeata).  We found quite a few individuals all with different color patterns.

 

We've been impressed with the diversity of marine invertebrates in the tidepools in Iceland and feel fortunate to be exploring and learning more about them.  We hope you enjoy meeting them, too!

Rock star?

  

Whew, we were busy with field work during the low tides this past week, but we managed to take a few photos on the side.  

Here's one that Eric took in Mendocino County today (23 May 2026) -- a beautiful Daisy Brittlestar (Ophiopholis kennerlyi) on the underside of a rock with clusters of small tubeworms. 

Upcoming

  

For all of the marine invertebrate enthusiasts out there — I wanted to mention that Eric will be presenting a webinar for Bay Nature magazine this week on Wednesday, Feb. 5, from 12-1 p.m. PST.  He'll be discussing the local diversity of marine invertebrates and some new discoveries, accompanied by lots of great photos and videos!

If you're interested in checking it out, you can register to join the talk online here.

P.S.  This is a Dwarf Brittle Star (Amphipholis squamata) photographed on Bodega Head last week.

Glass-spined

  

Glass-spined Brittle Star (Ophiothrix spiculata) photographed in Bodega Bay on 27 January 2025.

Spotted and striped

Just a quick photo of some nice Long-armed Brittle Stars (Amphiodia occidentalis) that Eric discovered in the intertidal zone in San Diego today:

 

 

The lowest individual is upside down, but check out the interesting color patterns, especially the spotting on the central disc between the arms.  [You can click on the image for a larger version.] 

 

There's an older NHBH about this species from 2013, so if you'd like to see a video of this species in action, see the post called "Fastest digger in the West".

Peanut brittle?

  

Okay, I know I've shown a few peanut worms recently, but this was a nice view of several different peanut worms (Phascolosoma agassizii) extending their introverts from a crevice and using the short ring of tentacles at the end to feed.  You can also see several arms of a brittle star extending out of the crevice and even lying across one of the peanut worms.

P.S.  If you want to play the "phyla game" again, look around to see what you can find.  Below I'll list the phyla in this image.

1. Peanut worm (Phascolosoma agassizii), Phylum Sipuncula
2. Brittle star, Phylum Echinodermata
3. Barnacle, Phylum Arthropoda
4. Limpet (checkered, in lower left corner), Phylum Mollusca
5. Tube worm (orange tentacles, upper right corner), Phylum Annelida
6. Flatworm (gray/white, same species as last night), Phylum Platyhelminthes

Orange dots

 

Glass-spined Brittle Star (Ophiothrix spiculata) photographed in the low intertidal zone along the Sonoma Coast on 1 January 2018.

 

Super star

Joe and Sam dropped by to say they had found something interesting in an aquarium at the marine lab.  I was a little surprised to look down and see one of the largest brittle stars I've ever seen!

 

We found a smaller Flat-spined Brittle Star (Ophiopteris papillosa) last year, but the size of this individual was notable.  The central disc alone was ~3 cm (~1 inch) across!

Here's a close-up of the disc:

 

 And a view of the flattened spines at the tip of one arm:

 

 

Amazingly, the largest specimens of this species have central discs up to 4.5 cm across!

Many thanks to Joe and Sam for sharing this impressive brittle star.

 

For a look at the smaller individual we photographed last year, along with a short video clip, see the post from 1 March 2017. 

Digging it

A few years ago, I introduced the Long-armed Brittle Star (Amphiodia occidentalis).  

 

You can review the earlier post here, but I'm excited to share even better footage of this amazing brittle star in action.

Take a look!

This video is shown in actual time.  Note the extremely long, flexible arms of the brittle star; the impressive digging behavior (the sand grains appear to be "boiling"); and close-ups of the tube feet flicking upwards.  The tube feet are visible on the under sides of the arms (below the spines) — watch for them especially during the interval at 30-35 seconds.

[If you can't see the video clip below, click on the title of the post above to go directly to the web site.]

longarmed_brittle_star_sanford from Jackie Sones on Vimeo.

 

I hope you dig this video as much as we did!

A little different

Remember the Glass-spined Brittle Star that was featured on 18 December 2016?

Well, we found one last weekend, but soon after Eric noticed a second brittle star and he knew right away that it looked a little different.  I snapped a quick picture of the two brittle stars side-by-side.  In the photo below, the Glass-spined Brittle Star is on the right.  Look for differences in the overall color; the patterns of banding along the arms; and the spines:

 

Eric managed to get a much better close-up of the second brittle star:

 

Meet the Flat-spined Brittle Star (Ophiopteris papillosa)!  Now you can see the distinctive arm spines — opaque brown, smooth, with blunt (rounded) tips.

And lucky for us, Eric also filmed this brittle star in action.  Here's a short video clip.  Watch for the very active tube feet (below the spines).  Many brittle stars move by "rowing" with their arms.  Although this species uses its arms, you'll see that its tube feet also play an important role in locomotion.  [If you can't see the video clip below, click on the title of the post above to go directly to the website.]

Crystal connections

Brrrr!  It was a chilly 30°F in Cotati this morning — a brisk morning in this part of the world.  Here are some frost crystals that were on my car in the front yard:

 

When we were looking at the frost this morning, we were struck by the similarities to something quite different:

 

Although they resemble sparkling frost crystals, these are the calcareous spines of a Glass-spined Brittle Star (Ophiothrix spiculata). You might recall an earlier post (from 9 November 2014) when I described how these brittle stars feed — by wiping their spines with their tubefeet to pick up small organic particles stuck on the sharp points and then transferring the particles to their mouth (on the underside of the central disc).

Recently, Eric captured some footage of this behavior.  First, here's another still image.  If you look carefully, you can see a long flexible tubefoot being drawn along one of the spines:

 

And, for an outstanding view of this feeding behavior in action, here's a video clip.  There are some general views of the brittle star crawling, and then watch for the feeding behavior between ~16-40 seconds. [If you can't see the video in the e-mail, click on the title of this post to go to the web page.]

Glass-spined Brittle Star from Jackie Sones on Vimeo.

Pretty amazing!  

Thanks to Eric for sharing these photos and the video clip.

P.S.  Stay warm, everyone!
 

Colorful discs

Last night I mentioned we've been finding some kelp washed up on the beach.  Recently, one Bull Kelp specimen still had a relatively large holdfast at the bottom of the stipe, shown at the right in the photo below.  (A smaller kelp, Laminaria setchellii, was also attached to the Bull Kelp holdfast.)

 

Eric and I have been doing surveys of holdfasts for several years, so we took a closer look at this one.

Almost immediately, Eric noticed some very nice Daisy Brittle Stars (Ophiopholus kennerlyi) on and inside the holdfast.

Here are two close-up examples:

 

 

We kept looking, and it turns out there were more than 35 individual brittle stars on this holdfast (and we probably missed some).  We were especially fascinated by the diversity of color patterns on their central discs. 

So we took pictures of many of the individuals, and then Eric did something pretty special, just for you!

You can click on the photo below to see a slightly larger version (and to truly appreciate these spectacular brittle stars!).

 

In some ways, it's hard to believe this variety is seen in a single species.  Daisy Brittle Stars are known for amazing variation in the colors and patterns of their central discs (and their arms).

Moment (1962) seems to have been one of the first scientists to document this phenomenon in a related North Atlantic species, Ophiopholus aculeata:

"...out of hundreds of individuals collected at low tide in about an inch of water in a single cove on the coast of Maine it is not possible to find two exactly alike."

Here are examples of the patterns in Moment's brittle stars:

 

From Moment, G.B.  1962.  Reflexive selection: A possible answer to an old puzzle.  Science 136: 262-263.

Moment (1962) proposed a possible reason for the variation.  He called it "reflexive selection."  The basic idea is that variable color patterns make it harder for a visual predator (e.g., a fish) to develop a search image for one particular color variant...so predators impose selection for variation per se.  This process can generate something known as "massive color polymorphism" where just about every individual is unique.  According to Owen and Whiteley (1986), "The massive diversity thwarts the learning processes of the predators..."

Eric's fascinating collage is a wonderful demonstration of this individual variation.  Of the twenty shown, do you have a favorite color pattern...or, do you just like the diversity?

Fastest digger -- Part 2

Do you remember the post about the "Fastest digger in the West" from November 2013?

Eric and I found two of these wonderful brittle stars — Amphiodia occidentalis — this past weekend.  Their arms are incredibly long!

This time we noticed the wonderful striped patterning on their arms, although one of the individuals was paler than the other (see pictures of both below).

 

 

And once again, the burrowing ability of this species was on display.  The next picture shows one of the brittle stars partially buried in the sand.  You can see how well the light and dark arm coloration matches the variable sand grains.  Click on the picture for a slightly larger version, and look closely for the central disc and the different parts of the arms disappearing below the surface:

 

P.S.  If you didn't see the earlier post about this species, it's worth watching the video clip!

Spinelets

Here's a mystery close-up for you.  Can you guess what this is?

 

If you'd like to see a little more, scroll to the next image:

 

Perhaps you have some ideas now?  If not, I'll zoom out one more time.  Warning: The next picture will reveal most of the animal:

Those wonderful spines belong to a brittle star known as Ophiothrix spiculata, sometimes called a Glass-spined Brittle Star.  Eric spotted it among the rocks in the intertidal zone last week.  This is the first time we've seen this species in Sonoma County.

The jagged edges of the spines are an important characteristic for identifying this species.  (The smaller spines along the edges of the larger spines are formally called spinelets.)  Ophiothrix spiculata belongs to a family of brittle stars that's primarily tropical in distribution.  It ranges from about San Mateo County to the Galapagos Islands.  There's a record from Victoria, B.C., but otherwise it seems most sightings are from Moss Beach and south.  It can be abundant in southern California.

The arms are usually very long, but this species is prone to autotomizing — dropping its arms (often in self defense, e.g., to escape a predator).  This individual had lost the tips of its arms, but it was regrowing them.  Here's a picture from the field:

 

One more fun fact about the Glass-spined Brittle Star.  Those spinelets come in handy when feeding.  After suspended particles in the water are trapped on the spines, the tubefeet wipe them off and move the food particles to the mouth on the underside of the disc.

 

Fairies of the holdfast

 

When we found these tiny pink brittle stars in a Bull Kelp holdfast recently, Eric called them "fairies of the holdfast."  Somehow it seemed like a perfect match.

I know it's hard to tell how small these animals are when there's nothing in the pictures for scale.  The individuals I'm showing in these first few images were only 5-10 mm across from arm tip to arm tip.

The smallest brittle star was the palest:

 

The largest was the pinkest:

 

Brittle stars species can vary quite a bit in overall size.  Some species are very small even as adults.  So at first I wasn't sure if these were full-size animals or not.  

When I looked under a microscope I noticed that there were lots of spines.  In the picture below, that's a small section of the brownish central disc in the lower right corner covered with tiny spines.  And that's one arm pointing to the upper left corner.  Even the dorsal arm plates and the lateral arm spines projecting out to the sides are spiny!  Although not a given, this made me suspicious that I was looking at juvenile brittle stars (rather than adults) as juvenile echinoderms are often very spiny.

 

While I was looking at these small brittle stars for identification clues, I was surprised to catch a glimpse of these at the tips of their arms:

 

Check out those hooks!  Wow!  I haven't looked at that many brittle stars under the microscope before, so I didn't know if these hooks were common.

We scanned a few books and I couldn't find a species description that mentioned these hooks until once again Philip Lambert (and William Austin) came to the rescue.  In their book, Brittle Stars, Sea Urchins and Feather Stars of British Columbia, Southeast Alaska and Puget Sound (1997) they describe hooks like this for the Daisy Brittle Star (Ophiopholus kennerlyi).  

Well, I am familiar with Daisy Brittle Stars as adults, but I hadn't identified juveniles before.  But it so happens that we had also found an adult Daisy Brittle Star on the same day.  I wondered if I could find the hooks on the adult.

 

The adult was very active...and the hooks were hard to see...but there they were!  Look closely to see them in the photo above.  They're adjacent and just to the left of each tubefoot.  (Yes, the tubefeet are papillated in brittle stars.)

I had lots of questions after that...I was hooked!  How do the brittle stars use these hooks?  For grasping the substrate?  Are they more important for juveniles than for adults?  Are they an adaptation for wave-swept environments?  Do the hooks play any role in capturing prey (as they do in basket stars)?  Could the hooks be used in defense?

I posted about adult Daisy Brittle Stars last February, so you can review those pictures here.  And if you'd like to see a closeup of the adult from this year, the following is an exceptional view of its central disc.  And now we know that Daisy Brittle Stars start out pale pink and brown and gradually transition to having a highly patterned disc and arms!

 

Fastest digger in the West

Think of the fastest digging animal you know of.  Now let me introduce you to an animal that might be faster. This is Amphiodia occidentalis, also known as a Long-armed Brittle Star.  

 

Eric found it under a rock in the low intertidal zone on Bodega Head.  After we identified it as Amphiodia occidentalis, we read this about it:

"...burrowing behavior is spectacular and is easily seen if an animal is placed on fine sand under water." 

Who could resist that?

Because this behavior is better appreciated through video, we're providing an action clip below.  Before you press play, keep two things in mind.  (1) It's tempting to focus on the central disk, but most of the action is happening along the arms.  So it's worth trying to watch the arms and to process how fast they are disappearing below the sand.  (2) We've actually done something a little unusual with this video — it plays forward and then in reverse (all in actual time, not sped up!).  We found that the brittle star disappears so quickly it's hard to understand what happened; seeing it in reverse somehow reminds you just how fast the arms sink below the sand.  [If you're reading this in an e-mail, you may need to click on the title of the post above to access the video on the web page.]

Amphiodia Blog from Jackie Sones on Vimeo.

Once buried, only the tips of the brittle star's arms remain above the surface for suspension feeding.

Here's a close-up of Amphiodia under the microscope:

 

It's hard to see them, but the amazing burrowing behavior is made possible by tubefeet located on the underside of the arms.  The tubefeet are long and flexible, and when they bend to kick up sand they fit neatly between the arm spines.

Because the tubefeet are transparent it was difficult to photograph them, but I've highlighted two of them with red arrows in the image below.  The upper arrow is pointing to a tubefoot that is bent and in the process of flicking upward.  The lower arrow is highlighting an extended tubefoot; note the smooth texture at the base (close to the arm) and the rough texture at the tip.

According to Intertidal Invertebrates of California, Amphiodia occidentalis may be found in a variety of habitats: under rocks in sand, in protected tidepools, near the roots of eelgrass, or in kelp holdfasts.  If you're lucky enough to find this brittle star, be sure to watch its magical disappearing act!

Take five

Dwarf Brittle Star (Amphipholis squamata), found in the low intertidal zone on Bodega Head on 28 April 2013 and photographed under a microscope.  It was ~15 mm across.

 

 

 

 

 

I could have stopped with that series of five images, but I was fascinated when I caught a brief glimpse of the underside of the brittle star.  Here's a close-up (below).  The mouth is the dark cavity in the very center of the disk.  But what's perhaps most interesting in this particular image is the white scale with a single pore to the left of the mouth.

 

That modified scale is the madreporite (or sieve plate).  Water is pulled in through the madreporite and enters the water vascular system which powers the tubefeet.  In sea stars, the madreporite is on the aboral surface (opposite the mouth) — for an example, see the salmon-colored spot on the Ochre Sea Star in the photo below. 

 

But in brittle stars, the madreporite is on the underside, adjacent to the mouth.  It's not often as visible as it is here, so this is a nice illustration of one of the differences between a brittle star and a sea star.

Here's another view with the madreporite in a slightly different position.  Can you find it?

 

The madreporite is in the lower right corner (remember it's about halfway between the mouth and the outer edge of the disk).  [If the brittle star was a clock, the madreporite is located between the arm that points to 3 o'clock and the arm that points to 6 o'clock.]

Although this brittle star was small, it revealed a significant lesson!