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Remember those little urchins I brought into the world back in January? Well, they're doing well, for the most part. About a month ago I took about 250 of them, measured them, and divided them into three feeding treatments:  one group I left on the coralline rocks they all cut their teeth on, one group is eating the green alga Ulva, and the third group is eating the kelp Macrocystis pyrifera. My plan is to keep the groups on these foods and monitor growth and survival.

After one month it appears that mortality and growth are not related. I have lost more urchins from the Macrocystis treatment than from the other two, and yet those that have survived this far have grown quite a bit. A month of the experiment gives me exactly two data points, which may over time indicate the beginning of a trend but for now are entirely meaningless. I'll have to wait at least another month to see if what's happening now continues.

However, I also took pictures of the urchins, and some of them are getting so pretty! I'm curious to see if the two macroalgal diets (Macrocystis and Ulva) affect the color of the urchins as they grow. Of course, color is very subjective and I can't duplicate the exact lighting conditions when I take microscope pictures of different subjects, so at this point they all look the same no matter which food they've been eating.

Juvenile Strongylocentrotus purpuratus feeding on Macrocystis pyrifera, age 167 days. 6 July 2015. © Allison J. Gong
Juvenile Strongylocentrotus purpuratus feeding on the kelp Macrocystis pyrifera, age 167 days. Major mark on scale bar indicates 1 cm. 6 July 2015.
© Allison J. Gong

and

Juvenile Strongylocentrotus purpuratus feeding on the green alga Ulva sp., age 167 days. 6 July 2015. © Allison J. Gong
Juvenile Strongylocentrotus purpuratus feeding on the green alga Ulva sp., age 167 days. 6 July 2015.
© Allison J. Gong

My most colorful urchin at the moment is a little guy from the Ulva food treatment. Its test diameter is only about 4 mm, but its color is very vibrant:

Juvenile Strongylocentrotus purpuratus, age 167 days. 6 July 2015. © Allison J. Gong
Juvenile Strongylocentrotus purpuratus, age 167 days. 6 July 2015.
© Allison J. Gong

In addition to the five distinct reddish-purple bands on the body, I like that this urchin has so much color on its spines. This individual looks like it may skip the green stage that urchins of this species go through and go straight to purple.

Aren't these animals beautiful?

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I did a quick search, and there doesn't seem to be a collective noun for sea stars. I'm going to remedy that by declaring "constellation" to be the official term for a group of sea stars. And by "official" I mean that's the term I'm going to use. Who knows, maybe it'll take.

In any case, I certainly have a constellation of sea star larvae in each of my jars. Today I pipetted a lot of them into a bowl, and they look pretty cool all swimming together, like strange alien spaceships. What do you think?

The largest of the larvae are over 2 mm long now, and the brachiolar arms have grown much longer. They have three adhesive papillae on the ventral side of the anterior projection and well-formed juvenile rudiments, where the water vascular system is forming. They're much too big to fit under the compound scope, so the only way to get pictures of the entire body is through the dissecting scope:

Brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015. © Allison J. Gong
Brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015.
© Allison J. Gong

In the above photo you are looking at the larva's ventral surface, so the animal's left side on the right side of the photo, and vice versa. If you squint you might be able to convince yourself that you see a small whitish bleb on the left side of the stomach; that's the rudiment. Since it doesn't make much sense under this magnification, I removed this individual to a slide and put it under the compound scope. It doesn't fit in the field of view, so I took pictures of each half of the body. If I were clever with photo editing software I'd be able to mesh these photos into a single image. Alas....

Ventral view of the anterior end of a brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015. © Allison J. Gong
Ventral view of the anterior end of a brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015.
© Allison J. Gong
Ventral view of the posterior end of a brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015. © Allison J. Gong
Ventral view of the posterior end of a brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015.
© Allison J. Gong

This gives you a better view of the juvenile rudiment on the animal's left. Those three roundish blobs are tube feet! I think it's likely that at some point in the not-too-distant future the larvae will be competent, which means they'd be physiologically and anatomically capable of metamorphosis. It seems to me that they are still developing very quickly, and with seawater temperatures consistent at 15-16°C I don't expect that to change. So far, so good!

Edit 4 July 2015:  Look at what my online friend Becca can do! She was able to merge my photos into a single image. Now you can see the entire body! Thanks, Becca!

Composite image of brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015.
Composite image of brachiolaria larva of Pisaster ochraceus, age 31 days. 3 July 2015.

 

You know how the saying goes. I just wanted to share how beautiful this larva is.

Brachiolaria larva of Pisaster ochraceus, age 20 days. 22 June 2015. © Allison J. Gong
Brachiolaria larva of Pisaster ochraceus, age 20 days. 22 June 2015.
© Allison J. Gong

I have nothing to add. More on Friday, probably.

 

What a difference a week makes! The Pisaster larvae have grown and developed quite a bit since I looked at them a week ago. Here they are as little space ships again.

Early brachiolaria larvae of Pisaster ochraceus, age 17 days. 19 June 2015. © Allison J. Gong
Early brachiolaria larvae of Pisaster ochraceus, age 17 days. 19 June 2015.
© Allison J. Gong

Since they are getting so big, Scott and I decided to redistribute the larvae from four jars into six. This will give them room to grow and ensure that they aren't overcrowded. To do this we first concentrated them all into a single beaker, then divided the entire population into two jars, then subdivided each jar into three jars, for a total of six. See all the larvae in the beaker?

Brachiolaria larvae of Pisaster ochraceus, aged 17 days. 19 June 2015. © Allison J. Gong
Brachiolaria larvae of Pisaster ochraceus, aged 17 days. 19 June 2015.
© Allison J. Gong

The largest larvae are ~1200 µm long, getting big enough to fill up the field of view under the lowest magnification of the compound microscope. The most noticeable difference from last time, aside from the overall increase in size, is that the ciliated band is becoming more lobed. These lobes will eventually be elaborated into the long arms of the mature brachiolaria larva ('brach-' is Greek for 'arm'). See below:

Brachiolaria larva of Pisaster ochraceus, age 17 days. 19 June 2015. © Allison J. Gong
Brachiolaria larva of Pisaster ochraceus, age 17 days. 19 June 2015.
© Allison J. Gong

The other rather obvious development is that the left and right coeloms from the previous observation a week ago have fused together in the anterior (top of the picture) and posterior (bottom of the picture) region of the body.

From here on out the larvae won't get too much bigger; if I remember correctly they'll grow until they're about 1500 µm long. Their brachiolar arms will get really long and pretty, though, greatly increasing the length of the ciliated band. Eventually their juvenile rudiments will form . . . but that's a post for another day. More on that when it happens.

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Today my Pisaster ochraceus larvae are 10 days old. Although they seemed to be developing slowly, compared to the urchins that I'm more used to, in the past several days they have changed quite a bit. They've also been growing quickly, which makes me think that they're off to a strong start. Of course, there's still a lot of time for things to go wrong, as they have another couple of months in the plankton. However, at this point in time I feel optimistic about their chances.

In the dish under the dissecting scope they swim around like bizarre space ships. All the bits of detritus in the water add to the effect. The only thing missing is the sound effects.

The magnification of my dissecting scope goes up to 40X. To see any details of anatomy I have to use the compound microscope, through which I can see this, under 100X magnification:

10-day-old bipinnaria larva of Pisaster ochraceus, 12 June 2015. © Allison J. Gong
Ventral view of 10-day-old bipinnaria larva of Pisaster ochraceus, 12 June 2015.
© Allison J. Gong

Aside from the dramatic increase in overall size (almost 1 mm long now!), the larva's body has gotten a lot more complicated. For one thing, the animal's marginal ciliated band, which propels the larva through the water, has started becoming more elongate and elaborate. In this view the larva is lying on its back, and I have focused on the plane of its ventral surface. The left and right coeloms are in the plane of the dorsal surface, and thus are not really in focus. You should still be able to see how long they have gotten, though. Eventually they will fuse anteriorly to form a single cavity. The stomach of the larva has a nice green-golden color due to the food it has been eating. It makes perfect sense, as we are feeding them a cocktail of green algae and a diatom-like golden alga.

The larvae are very flexible and can be quite animated when they're swimming around. They bend, scrunch up, and swallow food cells. They have already gotten so big that they take up much of the field of view under the microscope, even at the lowest magnification. Watch some larval gymnastics:


Part of the reason that I wanted to spawn Pisaster and raise the larvae this summer is that I want to put together a series of pen-and-ink drawings of the developmental stages. I did the same for the bat star Patiria miniata several years ago, but the Pisaster larvae will have longer and more elaborate arms when they mature; capturing these in drawings will be a challenge for me. I also hope to include the juveniles in this set of drawings. With that goal in mind, I've been sketching the larvae every few days, just to get some practice under my hand and remind myself what it feels like to draw. I've missed it!

10-day-old bipinnaria larva of Pisaster ochraceus, drawn from life. 12 June 2015. © Allison J. Gong
10-day-old bipinnaria larva of Pisaster ochraceus, drawn from life. 12 June 2015.
© Allison J. Gong

For whatever reason, I really like how this sketch turned out. It's not pretty, but it does truly represent what I saw under the microscope. I'm going to have to work on depicting three-dimensional structures on a two-dimensional page, which will take some practice. Fortunately I have several weeks to brush up on my skills!

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This spring and summer the local beaches have at times been covered by what appear to be small, desiccated, blue or white potato chips. They would typically be seen in windrows at and just below the high-tide line, or blown into piles. The most recently washed up ones are a dark blue-violet color, while the ones that have been on the beach for more than a day or two are faded to white.

Windrows of Velella velella (by-the-wind sailor) washed up on the beach at Point Piños, 9 May 2015. © Allison J. Gong
Windrows of fresh Velella velella (by-the-wind sailor) and algal detritus washed up on the beach at Point Piños, 9 May 2015.
© Allison J. Gong
Desiccated Velella velella on the beach at Franklin Point, 22 April 2015. © Allison J. Gong
Desiccated Velella velella on the beach at Franklin Point, 22 April 2015.
© Allison J. Gong

These animals are Velella velella, commonly called by-the-wind sailors. Taxonomically they are in the Class Hydrozoa of the Phylum Cnidaria. Other members of this class are the colonial hydroids and siphonophores (such as the Portuguese man-o'-war, Physalia) as well as the freshwater hydras that you may have played around with in high school. Technically speaking, Velella isn't a jellyfish. Actually, if we want to get uber-technical about it, there's no such thing as a jellyfish at all; or if there is, it's a vertebrate (i.e., some kind of actual fish) rather than a cnidarian. Most of the gelatinous creatures that people generally refer to as "jellyfish" are in fact the medusae of cnidarians.

That said, Velella is a special kind of hydrozoan. Its body consists of an oblong disc, 3-10 cm long, with tentacles and such hanging down and a sail sticking up. The little sail catches the wind that propels the animal:

Single Velella velella washed up on beach at Franklin Point, 22 April 2015. © Allison J. Gong
Single Velella velella washed up on beach at Franklin Point, 22 April 2015.
© Allison J. Gong

How do so many of these animals end up on the beach? The answer is that they float on the surface of the ocean and are at the mercy of the winds, hence their common name. This is an extremely specialized habitat called the neuston. Organisms living here have to be adapted to both aerial and marine factors. In fact, the blue pigment in these animals is thought to act as a sunscreen, reflecting the blue (and probably UV) wavelengths and protecting the underlying cells. We all know that UV radiation damages DNA, right? That's why we wear sun protection. Other cnidarian inhabitants of the neuston are things like Physalia and Porpita porpita (blue buttons), which are also blue in color. A former boss of mine used to say that for every hydroid there's a nudibranch that lives on it, eats it, and looks just like it. Porpita isn't exactly a hydroid, but it does have a predatory nudibranch, Glaucus atlanticus, which is (of course) blue-purple! Glaucus eats Velella, too.

Porpita porpita (left) and its predator, the nudibranch Glaucus atlanticus. Diameter of P. porpita approx. 2 cm.
Porpita porpita (left) and its predator, the nudibranch Glaucus atlanticus. Diameter of P. porpita approx. 2 cm.

 

 

 

 

 

 

 

 

The Monterey Bay Aquarium Research Institute (MBARI) has, of course, one of the best video explanations of what Velella is all about. I certainly can't do any better, so you should watch this:

By the way, MBARI's YouTube channel is like marine biology and oceanography porn. Just sayin'. If you have some time to kill on the Internet, you could certainly do worse than to spend it there!

Today the Pisaster larvae that Scott and I are following are a week old. Happy birthday, little dudes! Yesterday we did the twice-weekly water change and looked at them. They're getting big fast since we started feeding them on Saturday when their mouths finally broke through. At this stage they are sort of jellybean-shaped and extremely flexible--they don't have the calcified skeletal rods that sea urchin larvae have so they bend and flex quite a lot. They are also beautifully transparent, which allows us to see their guts in fine detail. We can even watch them swallow food cells!

Front view of Pisaster ochraceus bipinnaria larva, age 7 days, 8 June 2015. © Allison J. Gong
Front (ventral) view of Pisaster ochraceus bipinnaria larva, age 7 days, 8 June 2015.
© Allison J. Gong

In profile view you can see that the larvae are shaped sort of like fat C's. Here's a side view of a different individual:

Right side view of bipinnaria larva of Pisaster ochraceus, age 7 days. © Allison J. Gong
Right side view of Pisaster ochraceus bipinnaria larva, age 7 days.
© Allison J. Gong

In the short term (over the next couple of weeks or so) the larvae will continue to get longer. Their guts won't change much, but their coelomic systems will develop and become more complex. I'll try to capture that in photos and drawings to share with you.

 

I've been fielding questions about my recent sea star spawning work from people I've shared this blog with, which is a lot of fun! To streamline things and make the info available to anybody who might be following, I decided to put together a very brief FAQ-like post to address the most recent questions.

Question:  Can you watch the eggs divide in real time?

In a time-lapse sense you can watch cleavage divisions occur, but not in real time. What I can do is set up a slide on the microscope and leave it there for a while. The gradually warming temperature speeds up development to the point that I can sort of see the division in real time. Of course, the danger is that the embryo will cook on the slide. I generally figure that once I've pipetted some embryos onto a slide and dropped a cover slip on top of them, they're goners (it's not really possible to remove the cover slip without damaging the cells underneath it) so I feel marginally less bad about sacrificing a few to the gods of observation.

Questions:  I’m fairly certain that the stars can go back to the sea, but are you able to keep their eggs with them, too? How difficult is that transport?

Actually, my scientific collecting permit specifically states that I'm not allowed to return animals to the wild. If I needed to, I could apply for additional permits but it has never been necessary for the work I do. Surplus eggs and larvae, therefore, are discharged into the seawater outflow at the lab and do return to the ocean but the parents remain in my care.

Question:  Are orange and purple stars usually able to cross with each other?

As far as anyone has been able to determine, the color of stars has zero effect on whether two individuals' gametes are able to do the nasty together. The sea stars that I'm working with--Pisaster ochraceus, the ochre star--are broadcast spawners, meaning that each individual spews his/her gametes into the water, where fertilization and development occur. The stars are also synchronous spawners, meaning that if one individual in an area begins spawning other stars in the immediate vicinity will also spawn. After all, it does take two to tango, and to spawn while nobody else does is a tremendous waste of energy.

So yes, a purple star and an orange star should be able to mate without any problems... at least not any problems due to the parents' colors.

Question:  If so, what color do they end up being, statstically?

This is a very interesting question. Two of my colleagues are going to spawn Patiria miniata (bat stars) next week to address this. Their plans are to cross a Blue female with an Orange male, an Orange female with a Blue male, and both pure-color matings. They did a preliminary version of this experiment a couple of years ago but didn't end up with enough juveniles at a size that color could be ascertained; thus they couldn't calculate any statistically meaningful color ratios.

Questions:  Do you suppose that the wasting disease could be now in the genetic makeup? Any thoughts (unofficial of course) about this?

My thought is sort of the opposite, actually. The animals that we brought in from the field are all survivors of SSWS; if anything, I'd expect them to be resistant to whatever causes the plague, and to (hopefully) pass on this resistance to their offspring. Of course, there's no way of knowing if and how exposure to SSWS affects the quality of the gametes. It's quite possible that these survivors are less fit after the SSWS outbreak than they were before.

Question:  Purple Male with Purple Female developed well and purple Male with Orange female didn’t…some sort of incompatibility?

Well, given what I saw today the Orange (female) x Purple (male) cross almost certainly did not work. Fertilization occurred, but almost none of the embryos had any indication of normal development. Since we know the Purple male was able to mate successfully with the Purple female, we can infer that his sperm were fine. It could be that there was something going on with the Orange female's eggs; there were a lot of them, but maybe their quality just wasn't very good. Or perhaps we somehow mistreated and wrecked them the other day.

Any other questions? Use the Comments section to ask them, and I'll address them in a future post.

Wow, they weren't kidding about "early developmental asynchrony" in sea stars! This morning I looked at the embryos that I had started almost 24 hours earlier, and noticed two things right off the bat:

Thing #1:  Within the F1 x M1 (Purple female x Purple male) mating , developmental rates among full siblings were all over the map. Some embryos had progressed to the blastula stage, which is essentially a hollow ball of ciliated cells, while others were still in the early cleavage stages and rather a lot hadn't divided at all. In fact, with 24 hours of hindsight I can see that several of these eggs had not even been fertilized.

Embryos of Pisaster ochraceus, age 24 hrs. 3 June 2015. © Allison J. Gong
Embryos of Pisaster ochraceus, age 24 hrs. 3 June 2015.
© Allison J. Gong

My first reaction upon looking into the microscope and seeing all these assorted blobs was, "Oh, crap." But then I looked more closely at some of the embryos and realized that they had become blastulae!

Here's a picture of a blastula. This embryo is freely swimming inside its fertilization envelope, although it doesn't have a lot of space (remember that narrow perivitelline space from yesterday? that's all the elbow room it has). The hollow space in the center of the embryo is the blastocoel 'sprout cavity.' Given that the embryo hasn't grown (or even hatched) yet, it's still ~165 µm in diameter, the size of the original egg.

Blastula of Pisaster ochraceus, 3 June 2015. © Allison J. Gong
Blastula of Pisaster ochraceus, 3 June 2015.
© Allison J. Gong

The stage that precedes the blastula (a hollow ball of cells) is called a morula (a solid ball of cells). The embryo that is partially visible in the bottom of the above photo may be a morula. Imagine the following sequence of events: (1) an egg is fertilized by a sperm, forming a zygote; (2) the zygote undergoes a number of cleavage divisions, with the cells becoming more numerous and smaller in size; (3) at some stage a solid ball of small cells, the morula, is formed; (4) as cell division continues, the cells migrate toward the outside of the sphere, forming a cavity (the blastocoel) in the middle.

The blastula is a ciliated stage, and in this video clip you can see the cilia moving. I shot this video at only 100X magnification to capture as much depth of field as possible, and suggest viewing at full-screen. This should enable you to see the three-dimensional structure of the embryo, and that it is indeed a sphere.


Thing #2:  The F2 x M1 mating (Orange female X Purple male) isn't doing well at all. I looked at several slides and didn't see any embryos that were developing normally. They had all been fertilized, as I could see the fertilization envelope surrounding each egg, but most had not even divided. The ones that had divided were all strange and just plain wrong. Here, see for yourself:

24-hr embryos of Pisaster ochraceus, 3 June 2015. © Allison J. Gong
24-hr embryos of Pisaster ochraceus, 3 June 2015.
© Allison J. Gong

Many of the eggs are blurry because they're below the focal plane of the microscope. But see how many of them are undeveloped? And how, in the ones that have started dividing, the cells are disorganized and of different sizes? Typical echinoderm cleavage, as I see in echinoids (our local urchins and sand dollars) and in my other crossing of these ochre stars, results in a blastula made up of cells that are all approximately the same size. Most of these embryos, on the other hand, appear to consist of one large cell and a bunch of tiny ones.

I assume that these abnormal-looking-to-me embryos will not hatch, although I could be pleasantly surprised tomorrow. I don't yet have much of an intuition about these Pisaster ochraceus embryos, so this is a huge learning experience for me. I do expect to see hatching in the F1 x M1 cross tomorrow. Fingers crossed!

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A recent college graduate and fellow marine lab denizen (Scott) and I are collaborating on a project to quantify growth rates in juvenile Pisaster orchraceus stars. This is one of the intertidal species whose populations in the field and in the lab were decimated by the most recent outbreak of sea star wasting syndrome (SSWS). We are interested in seeing how quickly the stars grow once they metamorphose and recruit to the benthos, and hope that the information will help researchers guesstimate the age of the little stars that are now being seen in the field. This would in turn tell us whether the little stars are survivors of SSWS or post-plague recruits. I keep seeing people refer to them as "babies," but they could very well be several years old. We just don't know, hence this study.

Large, healthy specimen of Pisaster ochraceus at Davenport Landing. 20 May 2015. © Allison J. Gong
Large, healthy specimen of Pisaster ochraceus at Davenport Landing. 20 May 2015.
© Allison J. Gong

But before we get to measure juvenile growth we have to get through larval development, which is perfectly fine by me because I'm always up for observing marine invertebrate larvae. Two weeks ago Scott and I ventured into the field in search of prospective parents. We brought back eight individuals from two different sites, making sure to leave many more in place than we took away. It was actually rather gratifying to see how many hand-sized-or-larger P. ochraceus there were. This morning we met at 07:30 to shoot up the stars with magic juice and then wait for them to spawn.

We have injected the stars (Pisaster ochraceus) and are waiting for them to spawn. 2 June 2015 © Allison J. Gong
We have injected the stars (Pisaster ochraceus) and are waiting for them to spawn. 2 June 2015.
© Allison J. Gong

It has been a while since I tried to induce spawning in Pisaster, and I had forgotten how much longer everything takes compared to the urchins. For one thing, the magic juice itself isn't the same stuff that we use on the urchins, and works by an entirely different mechanism. The stars' response to the magic juice takes 1.5-2 hours, whereas if the urchins aren't doing anything 30 minutes after getting shot up they either need another injection or simply don't have gametes to share.

However, despite my misgivings the animals spawned. Two large females gave us enormous quantities of eggs, and three more donated trivial amounts that we didn't end up using.

This purple individual is the one we designated Female 1. See the huge piles of salmon-pink eggs?

Large purple female Pisaster ochraceus, spawning. 2 June 2015 © Allison J. Gong
Large purple female Pisaster ochraceus, spawning. 2 June 2015.
© Allison J. Gong

and

Large orange female Pisaster ochraceus, spawning. 2 June 2015 © Allison J. Gong
Female 2, a large Pisaster ochraceus, spawning. 2 June 2015.
© Allison J. Gong

Although we had to wait for a male to spawn, we finally did get some sperm and fertilized the eggs at about 12:30. Another thing I had forgotten was that Pisaster eggs, when shed, are lumpy and strange. I was used to the urchin eggs, which are usually almost all beautifully spherical and small. The stars' eggs are about twice as big, at ~160 µm in diameter. The lumpiness doesn't seem to hamper the fertilization process, as you can see below.

Fertilized eggs of Pisaster ochraceus, 2 June 2015 © Allison J. Gong
Fertilized eggs of Pisaster ochraceus, 2 June 2015.
© Allison J. Gong

In this photo you can see the fertilization envelope surrounding most of the eggs. In stars the perivitelline space (the space between the egg surface and the fertilization envelope) is very narrow, which makes it difficult to see the envelope; in urchins the space is much larger, and as a result the envelope quite conspicuous. The rising of the fertilization envelope off the surface of the egg is referred to as the slow block to polyspermy, a mechanical barrier that keeps multiple sperms from penetrating any individual egg. There's also a fast block to polyspermy, but it happens on a molecular level milliseconds after a sperm makes contact with the egg surface; you can't see it happen in real time.

Cleavage in stars proceeds much more slowly than it does in urchins, too. In embryological terms, "cleavage" refers to the first several divisions of the zygote, during which the cell number increases as the cell size decreases. This inverse relationship between cell size and number logically has to occur because the embryo can't get any larger until it has a mouth and begins to feed, which won't happen for at least a couple of days. It took our zygotes about four hours to undergo the first cleavage division.

2-cell embryo of Pisaster ochraceus, 2 June 2015 © Allison J. Gong
2-cell embryo of Pisaster ochraceus, 2 June 2015.
© Allison J. Gong

I left the slide on the microscope to warm up and speed development a bit, and about 45 minutes later was rewarded with this mishmash of embryos at different stages. Nine hours after we started this whole process, there were 2-cell, 4-cell, and 8-cell embryos, as well as eggs that had not divided yet.

Embryos of Pisaster ochraceus, about four hours post-fertilization. 2 June 2015 © Allison J. Gong
Embryos of Pisaster ochraceus, about four hours post-fertilization, 2 June 2015.
© Allison J. Gong

This asynchrony in early development is another way that stars differ from urchins, and it takes some getting used to. I expect that development will become more synchronized as the embryos continue to cleave, and that hatching will occur for all of them at about the same time, probably before Thursday. At least it won't take another 9-hour day to see how far they've come.

 

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