March Madness

Over the last few years, I've come to realize that March (and April) are good months to look for interesting pelagic invertebrates washing ashore on local beaches.  I'm guessing it has to do with the beginning of upwelling season, strong winds, and big waves.

So although some people call this time "March Madness" for other reasons, I've also come to know it by that name.  Partly because the intense weather during this month can feel somewhat "mad."  And partly because I'm "mad" about these fascinating animals that we don't get to see very often.

For example, if you look back at the blog during previous Marches and Aprils, we've documented a hyperiid amphipod living in a salp, sea angels, siphonophores, and salps.

A few days ago we came upon another species of salp.  It didn't look like much at first — mostly clear and elongate, with a large orange/reddish spot at one end.  This individual was ~5 cm long.

 

 

However, when we brought it in to identify it under the microscope, it was a different story!  Many of its organs were visible through the transparent body wall.  (Note that because the salp had washed up on the beach, there are scattered sand grains in the background.)

 

To make this easier, here's a diagram with some of the organs labeled: 

 

Modified from The Biology of Pelagic Tunicates (Bone 1998)

A salp has a similar body plan to its close relative the sea squirt (an ascidian), except that the salp's incurrent and excurrent siphons are on opposite ends of the body.  Water enters at one end and passes through a mucous net that is produced by an organ called the endostyle.  The mucous net is suspended between the endostyle and the gill bar and traps fine particles of food.  Periodically the food-laden net is rolled up and moved into the stomach to be digested.  The muscle bands contract to force water through the net and the excurrent stream of water also moves the salp via jet propulsion.

And now I'll go back and identify these same organs in the picture I showed above: 

 

 

Below is an even closer view of the heart and a portion of the gill bar and endostyle.  The tubular heart is intriguing because it periodically reverses its direction of pumping which drives the clear blood through the circulatory system in the opposite direction! 

 

I think this is Salpa fusiformis.  Although this species is known to occur along the West Coast, this is the first time I've documented it washing ashore in the Bodega Bay area.

For more general information about salps, you can review the post from 29 March 2013.

And here's a photo of March Madness weather when we found these salps:

 

Mystery below the sand

A few days ago, Eric and I were walking on Salmon Creek Beach and noticed an unusual pattern in the sand.  Most of the sand we'd been walking by had been very smooth, but this patch was marked with lots of nooks and crannies:

 

We decided to take a closer look to try to identify what was causing the pattern.  We started by swiping away the top layer of sand to see what was below.

This revealed a very high density of small animals!  Can you tell what they are?

 

To confirm their identity, Eric scooped up a small handful of sand and poured a little water over it for a better view of the animals:

 

Ah ha!  What an amazing number of juvenile Mole Crabs (Emerita analoga)!

I can't resist showing a few more pictures:

 

They burrowed into the sand very quickly.  Look for the paired dark eyes among the sand grains:

 

The next image is a little blurry, but I like it because Eric's fingers provide a sense of scale.  Each Mole Crab was ~5 mm long.

 

The entire roughened patch in the sand was about 6 meters long by 2 meters wide.  If the density of juvenile Mole Crabs was consistent across the patch, there were a lot of Mole Crabs in that area!

This made me think about the Sanderlings we observed feeding so intensively — see post from 24 March 2014.  Peter mentioned the possibility of them feeding on small Mole Crabs.  There are other options (e.g., amphipods or isopods), but it's intriguing to discover such a high density of juvenile Mole Crabs and to wonder about their vulnerability to shorebirds.

Coming to you from Westfield, MA

 

This is an interesting nemertean, or ribbon worm, that Eric found in a kelp holdfast a couple of weeks ago.  When fully extended, it was ~8 cm long.

The first features we noticed were the chocolate brown coloration, the cream-colored rings, and the bright white borders to the head.  

When viewed from the side, we were impressed with this ribbon worm's extremely long cephalic grooves (see below) — look for the slit or furrow along the lower edge.

 

At the posterior end there was a long appendage called a caudal cirrus (next picture).

 

After looking at all of these features and checking The Light and Smith Manual (2007), we were pretty sure this was Micrura wilsoni.  We looked for photographs online to confirm, but unfortunately couldn't find any pictures.  Eventually we located a copy of Wesley Coe's Nemerteans of the West and Northwest Coasts of North America (1905) with its wonderful set of color plates.

And there was Micrura wilsoni on Plate 3! 

 

Modified from Coe, W.R. (1905). Nemerteans of the West and Northwest Coasts of North America.  Bulletin of the Museum of Comparative Zoology 47: 1-319.

If you look closely at the drawing above, you can see a red spot at the back edge of the head.  We wondered what that was, so we read the species description.  Coe and the illustrator were highlighting the rosy-colored brain of Micrura wilsoni!  Could we see the brain in this individual?  Sure enough, in the right light, a reddish glow was visible (see below).

 

A few more fun things about Micrura wilsoni —

Sometimes it would contract and look somewhat like a leech:

 

Other times it would move via peristalsis — a series of wave-like muscle contractions: 

 

We wondered who Micrura wilsoni was named after.  Surprisingly, there's a connection to western Massachusetts!  Coe says: 

"The species is named in honor of Prof. C. B. Wilson, of Westfield, Mass., well known for his work on Nemertean development, to whom I am indebted for several specimens of this and of other Nemerteans, and for valuable notes on a number of the species described in this paper."

P.S.  Last March, we found a different species of Micrura in a kelp holdfast.  Click here for pictures of Micrura verrilli. 

Jagged blue

Just a few quick pictures of a chiton found in a kelp holdfast a couple of weeks ago.  It was ~14 mm long.

 

The jagged blue lines against the bright orange background of the plates were striking:

 

I'm still working on the identification of this chiton.  It's probably a species of Mopalia.  For this group, the number and arrangement of bristles on the setae (or hairs) along the edge of the chiton are important:

 

I hope to enlist the assistance of a Mopalia expert and will report back if we can confirm which species this is.

March flowers

Once again I have Michelle and Kyle to thank for sharing some spring wildflowers with me...and with you!  Here are two highlights from a walk last weekend near Occidental.

 

 

Few-flowered Collinsia or Spinster's Blue-eyed Mary (Collinsia sparsiflora)

 

 

California Saxifrage (Micranthes californica, formerly Saxifraga californica)

I was especially intrigued by the saxifrage flowers (below).  I think the colorful structures are the stamens — the male reproductive parts that release pollen.  However, what's the difference between the red and purple stages?  Are the little red parts (that look a bit like hearts) "covers" that will eventually fall off to reveal the purple and orange parts below?  (Is the orange pollen?)  If you know, please write in!

 

Touching down

 

 

 

 

 

Seventeen Whimbrel (Numenius phaeopus) touching down on Salmon Creek Beach, 26 March 2014.

Offshore showers

 

After a winter with so few rainy days, it was nice to see some showers offshore today (25 March 2014).

 

Magnetic attraction

About a week ago we came across a flock of Sanderlings on the outer beach.  They were in the swash zone, but didn't seem to be feeding there.

 

Soon they would run up the beach towards this one discrete, darkened patch in the sand:

 

And then they would start to probe very actively.  Below, note the difference in sand texture at the top and bottom of the picture.  (The smooth sand at the top of the picture is outside of the probed area.)

 

After a few minutes, the Sanderlings would run back down the beach to the water's edge.  But they couldn't seem to stay away from this patch.  It was like a magnet to them!  They would return to the patch over and over again.  There must have been a high density of prey at that site!

As the Sanderlings made their way to the water, their bills were noticeably coated in sand: 

 

Just looking at this picture makes me want to shake my head (to get the sand off).  And that made me wonder about why the Sanderlings were returning to the water every now and then.  Were they washing the sand off their bills in between feeding bouts?

 

Dynamite Dynamenella

 

Amazing, right?

How about another one? 

 

And a couple more?

 

 

We think these wonderful isopods are Dynamenella dilatata.  Eric spotted them in a Bull Kelp holdfast.  They ranged in size between 5-10 mm long.

There are a couple of important characteristics to pay attention to.  Believe it or not, the dynamite color pattern isn't one of them!  

According to the identification key in The Light and Smith Manual (2007), Dynamenella dilatata has (1) a distinctive "forehead" — that is, the frontal margin projects forward as a quadrangular process; and (2) inflated antennules — that is, the first two articles of the antennules are dilated.

Here's a closer look at both of those characteristics.  Note how there's a flat "shelf" in front of the eyes, and that the bases of the antennules are quite large.  The inflated antennule bases give this isopod a "moustached" appearance.

 

In this diagram of Dynamenella dilatata (see below), you can see the projecting frontal margin on the head, and the inflated antennules.  In the lower drawing, note also the three parallel ridges in the center of the pleotelson (basically the tail). 

From Richardson, H.R.  1899.  Key to the Isopods of the Pacific Coast of North America, with Descriptions of Twenty-two New Species.  Proceedings U.S. National Museum 21: 815-869.

These three raised ridges were easy to see on the larger isopods.  Look for them in the following image.

 

If you want to look at one more thing...or perhaps you've already noticed this?  The smaller individuals (first two images) have a shallow notch at the tip of their pleotelson.  The larger individuals (images three and four) have a very deep notch, like a keyhole (and see image directly above).

We don't know if the depth of the notch is related to the size of the isopod, and if all individuals will develop deeper notches as they get larger?  Or if the depth of the notch might indicate a difference between males and females?  Does someone out there know the answer?  The deeper notch was a little confusing to us at first because it isn't mentioned or illustrated in any of the identification keys.

We had trouble finding information about Dynamenella dilatata.  But Jim Carlton was kind enough to answer a few questions for us.  It appears as though their range extends from British Columbia to southern California.  [Jim told us that he knows of records between Washington and southern California, and there's an unidentified picture of what appears to be Dynamenella dilatata in Marine Life of the Pacific Northwest by Lamb and Hanby (2005).]

I don't know why Dynamenella dilatata is so colorful, or so variable, but it's fun to wonder about!

 

A teaser

 

This will have to be a bit of a teaser.  I'm having some technical difficulties with the blog tonight, so we'll continue this post tomorrow!  

A dynamite little isopod, isn't it?

The Stowaway

This is the final installment of The Velella Chronicles (at least for now!).

While I was watching the gonozooids feeding, something amazing happened.  A small, brownish, worm-like object became visible among the gonozooids.  It's at the top center of this image:

 

I struggled to understand what was happening at first...was this a part of Velella that I hadn't seen before?  But then it emerged fully and I could see that it was a completely separate animal.  Ah ha!  A stowaway!

 

The mystery animal was generally long and slender, but it was sometimes thicker and rounder in the middle.  And the anterior end (on the left) would sometimes contract dramatically:

 

One gonozooid began opening its mouth extremely wide as the stowaway approached.  You can follow the progression of the mouth opening by watching it in the upper right corner of these pictures (start with the first picture of the post above).

The stowaway started crawling along the rim of the open mouth:

 

Here it is fully on the rim, moving to the left: 

 

At one point it started "reaching around" and exploring the opening to the mouth:

 

And then I couldn't believe it, but the stowaway crawled into the mouth of the gonozooid!  The gonozooid didn't seem in a hurry, but it slowly closed in on the stowaway so that all I could see was the posterior end of the stowaway sticking out of a small opening (see below).  And then the stowaway disappeared completely inside of the gonozooid!

 

Wow.  What just happened?  Was the stowaway some sort of parasite?  Did the gonozooid eat the stowaway?  Or would the stowaway have some way of protecting itself against being digested by the gonozooid?

I haven't heard anyone talking about parasites of Velella velella.  And I wasn't really sure where to start learning about them.  Doing a quick search on the Internet didn't reveal much.  But I did find one reference to parasitic flatworms (trematodes and cestodes) in comb jellies, jellyfish, hydrozoans, and siphonophores.

One trematode genus was mentioned that seemed to have potential — Opechona spp.

I don't know if this stowaway is a species of Opechona, but it *might* be a trematode larva.  So it's worthwhile to talk about a basic trematode life cycle, with Opechona as an example.  This gets complicated, but here's a diagram to help visualize the different stages (with an explanation below).  The inner circle shows the life stages of the parasitic flatworm, while the outer circle shows the transitions between its three hosts:

 

Modified from Marcogliese, D.J. 1995. The role of zooplankton in the transmission of helminth parasites to fish. Reviews in Fish Biology and Fisheries 5: 336-371; Koie, M.M.  1975.  On the morphology and life-history of Opechona bacillaris (Molin, 1859) Looss, 1907 (Trematoda, Lepocreadiidae). Ophelia 13: 63-86; and  Siphonophores and Velellids by Kirkpatrick and Pugh (1984)

The stage we saw on Velella was possibly a free-swimming cercaria larva.  Once inside Velella it will lose its tail and encyst in a stage called a metacercaria.  If a fish eats Velella, then the metacercaria will develop into an adult fluke inside the fish (the definitive host).

The adult fluke can reproduce sexually with other flukes.  Fertilized embryos develop into miracidia larvae which leave the host with feces.  Once in the water, the miracidium larva locates and bores into the first intermediate host (e.g., a snail).  

Several additional larval stages occur within the snail (e.g., redia) before free-swimming cercariae leave the snail in search of the second intermediate host (e.g., Velella).

Whew!  Again, we're not sure about the identity of this stowaway, but it's fascinating to think about possible parasites on board Velella velella.