End of a long odyssey

For Eric’s summer class, we used a small plankton net to collect some plankton near the mouth of Bodega Harbor during a flooding tide last week.  The students sorted through the plankton sample in lab to see what larval forms they could find.  One of the students (Zack) spotted an amazing larval form.

This is a brachiolaria, a late-stage larva of a seastar, that appears to be the Ochre Seastar (Pisaster ochraceus).  The photo above was taken under the microscope, but the specimen is quite large for a planktonic larval stage, close to 2 mm long and visible with the naked eye. This larval form is beautiful and alien in appearance and doesn't look much like an adult seastar!   

A surprising feature of the brachiolaria larva is that the juvenile seastar begins developing within the transparent larval body.  In the photo above, the juvenile body is visible near the bottom of the larva and is shiny white in color.  With a closer view, you can see that the developing juvenile body already includes the start of calcareous ossicles that will become the internal skeleton of the juvenile and adult seastar!  In the photo below, the developing ossicles look like intricate snowflakes (white arrow).

 

This brachiolaria appeared to be nearing the completion of its planktonic larval phase, which can be a long odyssey in seastars.  Under laboratory conditions, the planktonic phase has been reported to last from ~40 to 228 days in Pisaster ochraceus, depending on temperature and food.  Pisaster spawns in the spring in California, so this larva likely spent at least several months at sea before entering Bodega Harbor.

When the brachiolaria returns to a rocky shore and finds suitable habitat, it will initially attach to the rock with a short stalk.  Remarkably, the transparent larval body is reabsorbed into the juvenile body during a dramatic metamorphosis. Soon after settlement, the juvenile sea star breaks off its stalk and crawls away as a tiny sea star. 

The larval phases of a sea star.  Illustrations compiled and modified from various sources.

Eric was able to capture some video under the microscope of this beautiful sea star larva.  In the video, notice the long ciliated larval arms used for swimming and gathering food from the plankton. You will also see a close-up of the developing juvenile body (white in color) and the snowflake-like ossicles.  (If you can't see the video player below in the e-mail message, click here to go directly to the video.)

With many thanks to Zack for spotting this planktonic wanderer!  And to Eric for his microscope camera skills and the helpful diagram.

P.S.  For more information about development in sea stars, see earlier posts on the larvae of the Bat Star (Patiria miniata) — "A new star(t)" in 2013 and "A profound change" in 2023.

P.P.S.  As a reminder, when juvenile Pisaster are first visible to human eyes in rocky shore areas, it's about 4-6 months after metamorphosis.  Here's an example of one that's about 4.5 mm across (between ¹/₈ inch and ³/₁₆ inch), photographed in November 2014.

 

Close to the bark

  

I returned home from the farmers' market to hear a Brown Creeper calling in our front yard.  Luckily my camera wasn't too far away, and the creeper spent some time feeding in a few different trees.  

Here it is searching crevices in the bark:

 

 

The creeper appeared to be successful locating prey, but the prey was too small for me to see while watching.  However, zooming in on photos later revealed a couple of prey items.

 

A small insect larva at the tip of the bill:

 

 

 

 

And possibly a small spider?

 

 

 

 

Turned out there were two creepers, both feeding along different tree trunks.

 

I love how well Brown Creepers blend in with the landscape of the trees—  the bark and lichens and mosses:

 

 

 

I'm also grateful for such wonderful visitors to our yard!

A profound change

  

For Eric’s class this summer, he raised the early life stages (larvae) of the Bat Star (Patiria miniata).  Eggs and sperm from spawning can be mixed in the laboratory to produce fertilized embryos.  Like many marine invertebrates, the fertilized embryos of sea stars develop into a swimming larval stage that looks very different from the adult form.  The photo above shows the larval stage (called a brachiolaria) of the Bat Star about 25 days after fertilization.  This stage uses cilia to swim through the water as it feeds on phytoplankton. 

By about 45 days after fertilization, the juvenile sea star is starting to form at the base of the larval body.  In the photo below, the golden-white dome-like section is the developing juvenile body (called the juvenile rudiment), which is already forming its skeleton (made of shiny calcareous plates called ossicles) and its tube feet (that it will use to crawl on the bottom).  

 

At this point, the larva is ready to make its way back to the rocky shore where it will attach and metamorphose into a juvenile sea star!  Metamorphosis requires profound changes, as the larval arms and larval body (transparent structures in image above) are completely reabsorbed into the juvenile body.

Now for the best part.  Eric was able to capture some microscope video of the bat stars over the course of their development!  In the video below you will see the larvae swimming about at ~25 days (where the pink structure is their stomach), and at ~45 days (with the developing juvenile body clearly visible).  In the final video clips from about 50 days, you will see the metamorphosed juveniles walking along the bottom using their first tube feet.  These new juveniles are very tiny (< 0.5 mm across)!

[If you can't see the video player in your e-mail, click on the title of the post above to watch the video on the NHBH website.]

You can read more about this amazing process of development in Bat Stars in some previous posts, "A new star(t)" on 12 August 2013 and "First steps" on 8 August 2017.

P.S.  Many thanks to Ellie and Christina for spawning the Bat Stars, and to Eric for the great video!

Leaving the lair

  

Okay, have you been wondering about the Turquoise Dragon and her developing larvae?  (See posts on 24 July 2023 and 29 July 2023.)

The larvae hatched on 2 August 2023 and Eric caught some of them crawling and swimming away in the video clip below.

The epitoke (reproductive stage of the worm) brooded the embryos/larvae for at least 12 days.  It's likely that the larvae will spend some time swimming in the plankton and growing (adding more body segments) before settling to the bottom and metamorphosing into juvenile worms.

[If you can't see the video player in your e-mail, click on the title of this post above to directly to the NBHB website.]

Thanks to Eric for sharing this great video clip!

The Dragon's Treasure

 

 

As you’ll recall, last week Eric’s class found an amazing reproductive worm swimming in the plankton (see "Turquoise dragon!" on 24 July 2023).  She was protecting a brood of fertilized eggs, but they were very early in development.   

 

Eric kept the worm in the lab, and now about a week later her embryos have developed into a treasure hoard of crawling 4-eyed larvae (called trochophores).  We suspect that sometime soon the larvae will break free of the brood sack and swim away!   

 

Here's a short video clip where you can see the larvae.  They're quite active!  [If you can't see the video player below, click on the title of this post to watch the video on the NHBH website.]

 

The Dove Snail Attacks!

I had a bit of an eyebrow-raising experience today.  I was trying to photograph a common snail, the Carinate Dove Snail (Alia carinata).  This marine snail can be found in a variety of habitats, e.g., rocky shores in tidepools and among surfgrass and seaweeds and in harbors among eelgrass.  It's fairly small (most individuals are probably ~10 mm long), elongate, and usually brownish/black in color.  Here's an example:

 

 

This species is common enough that you can overlook it.  But I needed a photograph, so I was looking at several of them under a microscope today when I came across one in a puzzling position.  I wasn't sure what was going on at first:

 

 

 

So that's the snail, with its siphon extended up and to the right and its foot flat against the surfgrass blade (in this photo the foot has blue highlights).  You can see the snail's short tentacles, and you can also see a small dark eye on the right hand tentacle.  But what's below the tentacles?  Here's a side view:

 

 

 

Ahhh!  The snail had extended its proboscis (a tubular feeding structure) into an egg capsule filled with developing larvae.  It was vacuuming up the veliger larvae!  I hadn't seen this behavior before, so I wasn't sure I was interpreting it correctly at first, but there was no doubt.  The snail reached around inside the egg capsule and cleaned out almost every developing larva.  (The egg capsule/larvae belong to a different snail species, Lacuna marmorata.)

 

Even better, Eric wasn't far away and he came over just in time to capture a video of this fascinating feeding behavior (see below).  

 

I loved learning something new and unusual about a common local snail.  In some ways the name "dove snail" suggests a rather sedate snail, but I'll never look at Alia the same way again!

 

And here's the best part — the video!  Watch for the snail approaching the egg capsule, inserting its proboscis inside, then using suction and its tongue-like radula to ingest the tiny larval snails.  You'll see the radula flicking in/out at the tip of the proboscis.  (At this stage, the larval snails have shiny little shells.)

 

 

 

Many thanks to Eric for a memorable video!

 

Mystery on the tidal flats

Last week Eric and I were exploring the tidal flats in Bodega Harbor when we noticed these patches of orange and white in shallow pools on the surface of the mud:

 

 

 

When we looked closer, we could tell that something had been spawning — releasing eggs (orange) or sperm (white) — but we weren't sure what type of animal was responsible.

 

Here are two close-ups showing the vast number of eggs:

 

 

 

 

 

 

 

We kept wondering who was releasing these eggs/sperm, and eventually we came across an animal in the act of spawning:

 

 

 

This is a fairly large polychaete worm.  We're not sure which species it is, but after consulting with some experts, it's possible it's in the family Amphinomidae.  [I'll update this post if we learn more.]

Many marine invertebrates reproduce by broadcast spawning — releasing gametes into water.  The strategy involves some luck in that the sperm need to encounter the eggs.  In the situation below, you can see how that might happen (with the sperm drifting over the eggs), but if they were farther apart, it might be less likely:

 

 

Although many marine invertebrates spawn in this manner, you don't get to see it that often in the field.  Because larval forms can sometimes be useful for species identification, we decided to mix some eggs and sperm together to see if they'd develop into planktonic larvae in the lab.  A week later, here's what we found under the microscope!

 

 

 

This is a larval form called a trochophore.  Those long spines (or chaetae) are likely used to defend the larva against predators and might also slow sinking in the water (they can spread the spines out to the side).  Many worms might spend weeks developing and growing in the plankton before undergoing metamorphosis into a juvenile worm that will burrow in the mudflats.

 

Many thanks to Eric for this wonderful photo of a fascinating trochophore larva!

 

P.S.  For a couple of other examples of broadcast spawning, see the posts called "Fortuitous" on 28 June 2013 (sea anemones) and "Broadcast news" on 2 May 2019 (sea stars).

 

Pelagic Red Crab zoea!

Okay, here we go — the answer to last night's mystery photo.  As a reminder, here's the image:

 

We received several correct guesses.  This is the zoea (free-swimming larval stage) of a Pelagic Red Crab (Pleuroncodes planipes)!  The photo below shows the entire zoea:

 

We haven't been able to find many pictures of Pelagic Red Crab larvae, so we thought it would be fun to share a few.  Eric also recorded some video (see below)!

Here's the basic sequence of events:

After finding live Pelagic Red Crabs on 24 January 2017, I was measuring them and counting the number of males and females.  I discovered that several of the females were carrying eggs.  Similar to lobsters, they brood their eggs attached to the underside of the abdomen (see below):

 

We wondered if the embryos would develop in Northern California waters.  Based on a previous study that found they did well at 12°C, it seemed like they should develop and hatch in ~22 days.

Right on schedule, the embryos hatched today (after a minimum of 22 days)!  This is what we saw when we came into the lab this morning — an adult female surrounded by hundreds of larvae, each ~2 mm long:

 

And here's a close-up of some of the larvae in the jar:

 

Carl Boyd described the larval stages of Pelagic Red Crabs in 1960.  This drawing shows the first zoea:

 

Modified from Boyd, C.M.  1960.  The larval stages of Pleuroncodes planipes Stimpson (Crustacea, Decapoda, Galatheidae).  Biological Bulletin 118: 17-30.

And here's a close-up of a zoea in a similar position (shown in dorsal view, from above):

 

As mentioned, Eric took advantage of a rare opportunity to film some live Pelagic Red Crab larvae.  You'll see the very active newly-hatched zoeae zipping around.  (Among the swimming sequences and close-ups, watch for the rapidly beating heart.)  Note: If you receive this via e-mail and can't see the video file below, click on the title of the post above to go directly to the web site.

pelagic_red_crab_zoea_sanford from Jackie Sones on Vimeo.

 

I can't help showing a couple more pictures — two extreme close-ups.  Check out the beautiful telson (last abdominal segment or "tail")...

 

...and the wonderful second antenna (the outermost antenna, adjacent to the eye):

 

We feel very fortunate to have observed and photographed these fascinating larvae.  We hope you enjoy them, too!