Tag: marine invertebrates

A little less confounded now

Posted on by Allison J. Gong

So. Last week when I looked at my sand dollar larvae I wasn’t at all sure what to make of them. I thought that all of the offspring from one of the matings (F2xM1) were going south and didn’t know how much longer they would survive. The offspring from the other two matings seemed to be doing much better.

Fast forward a week and a half and my, how things have changed. I have some juvenile sand dollars now! And so far they are all from the F2xM1 mating, the ones that had started looking strange and that I thought might die. I’m surprised that any of the larvae metamorphosed, as my general understanding of sand dollars was that competent larvae settle among adults of their species, so that when they finish metamorphosis they would be in a suitable location to grow up. However, the animals is always right, and in this case I was happy to learn that my understanding was wrong.

This larva is almost competent. The main part of its body is almost completely filled by the juvenile rudiment (the tannish structure on the left side of the more reddish stomach) and the arms are shorter.

Almost-competent pluteus larva of Dendraster excentricus, age 30 days. 22 April 2016 © Allison J. Gong
Almost-competent pluteus larva of Dendraster excentricus, age 30 days.
22 April 2016
© Allison J. Gong

And here is a video of a trio of competent larvae.

Their bodies are almost entirely opaque now but they are unquestionably pluteus larvae.

As metamorphosis begins, the tube feet in the juvenile rudiment rupture through the body wall and the animal starts sticking to a hard surface, in this case a glass slide. For a while the animal is suspended between the larval and juvenile forms, in a state I call a larvenile. Hopefully the time spent in the larvenile stage is short, as to be neither larva nor juvenile is a bad thing. I’ve seen both sea urchins and sea stars get stuck in the larvenile stage, and they all died.

Larveniles are strange things. See for yourself.

In this video the right side of the animal (not the anatomical right but the right side of the image as it is presented on the screen) is the juvenile, and the left side is the larva. The larva half still has its fenestrated arm rods, which will eventually be dropped and left behind. It also retains for the time being the ciliated band which it used both to swim and to capture food. Another weird feature of the larvenile is the transition between the bilateral symmetry of the larva and the pentaradial symmetry of the juvenile. The bilateral symmetry has been more or less obliterated by the process of metamorphosis, but there isn’t enough of the juvenile to have complete pentaradial symmetry yet.

And, finally, metamorphosis is complete and a little sand dollar walks around on tube feet.

Yesterday this animal was a larva, and today it’s a juvenile. The sea urchins do the same thing. But these sand dollars have done everything faster than the urchins, and that includes development immediately after metamorphosis. You may recall that the purple urchins have only five tube feet when they metamorphose, and they struggle to coordinate them to walk. From what I can see these sand dollars have at least twice that many tube feet very shortly after metamorphosis, and they can walk much more quickly.

The tube feet themselves are different, too. Urchins’ tube feet are suckered and look like little plungers. Sand dollars’ tube feet have those pincher-looking tips (although I haven’t seen them open up and grab things yet). Adult sand dollars live partly buried in sand and don’t use their tube feet to cling to surfaces; they do use their tube feet to grab food, though.

Speaking of food, I don’t know what these juvenile sand dollars will be able to eat. Fortunately I have a while to figure out what to try feeding them, as their mouths won’t open up for at least a week (I hope). While it’s easy to observe what happens on the surface of the animal as it metamorphoses, it’s impossible to see what’s going on with the internal reorganization of the body. I do know that an entire new gut will have to be formed before the animal can eat. In the meantime it will have to survive on energy stores stashed in all that opaque part of the body.

Stay tuned!

Confounded

Posted on by Allison J. Gong

Remember that one batch of sand dollar larvae that were looking weird on Monday? Well, they still look weird. In fact, all of the larvae looked the same yesterday as they did on Monday, which seems strange, considering how quickly they galloped through development for the first three weeks of larval life. It’s as though they’ve entered some stasis period during which developmental progress slows way down. Or maybe I just can’t see the signs of change.

Pluteus larva of Dendraster excentricus, age 23 days. 15 April 2016 © Allison J. Gong
Pluteus larva of Dendraster excentricus, age 23 days. Mating: F2xM1. Diet: Rhodomonas only
15 April 2016
© Allison J. Gong

If I had seen these larvae for the very first time yesterday, I might not suspect that anything was strange. But having watched them twice weekly since fertilization and knowing how different they looked a week ago, my Potential Weirdness-o-Meter™ is redlining. These larvae have definitely changed in a week, and not in the way that I’m used to echinoid larvae developing. With their much shorter arms and overall stunted appearance, these guys appear to be regressing. However, they aren’t dying and they don’t really look bad. As I said on Monday, they just look . . . weird.

Remember how I said I’d split this cohort of larvae into two batches and fed them different things? At first I thought this strange appearance was due to the change in diet from a Rhodomonas/Dunaliella mixture to Rhodomonas only. The larva in the photo above was from the Rhodomonas-only jar, and perhaps its odd appearance could be explained by some deficiency in the monoculture diet. Then I continued on my rounds and looked at the larvae from the same mating that were still on the Rhodo/Dun diet.

Pluteus larva of D. excentricus, age 23 days. 15 April 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 23 days. Mating: F2xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong
Pluteus larvae of D. excentricus, age 23 days. 15 April 2016 © Allison J. Gong
Pluteus larvae of D. excentricus, age 23 days. Mating: F2xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong

All the larvae in these photos remained on the mixed diet, and they look pretty much the same as their siblings eating the monoculture diet. So I don’t think the change in diet explains the appearance of the larvae.

Okay, then. If it’s not the food that accounts for what these larvae look like, maybe it’s something about the mating itself. These larvae, from both food treatments, are all full siblings from one mother mated with one father. As full sibs they share, on average, 1/4 of their DNA with each other, which could account for the similarity in their appearances. Perhaps this “strange” look is due more to genetics than to the environment (i.e., food).

I can test this hypothesis by examining larvae from the other crosses. Rather fortuitously, as it turns out, when I spawned the adult sand dollars a little over three weeks ago now, only one male contributed enough sperm for me to use. Three females spawned usable amounts of eggs, so I set up three matings:

  • F1xM1
  • F2xM1
  • F3xM1

The female designated F2 gave the most eggs, and her offspring are the ones that I split into the Rhodo-only and Rhodo/Dun diets. Note that all of the larvae in this little experiment have the same father. This gives me the opportunity to test for maternal effects on development; in other words, having controlled for the effects of different fathers–ha! I make it sound as though I did that on purpose–I can now assume that differences (in growth rate, survivability, and successful metamorphosis if we get that far) between the different matings are at least partially due to differences in egg quality among the three mothers. Or to differing gamete compatibilities between each female and the one male.

So now let’s take a look at the larvae from other matings. We’ll start with F1xM1:

Pluteus larva of D. excentricus, age 23 days. Mating: F1xM1. Diet: Rhodomonas/Dunaliella mix. 15 April 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 23 days. Mating: F1xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong

This larva looks normal to me, or at least what I’ve come to assume is normal. And wow, that was one filthy cover slip,wasn’t it?

The offspring of the F3xM1 mating look very much the same:

Pluteus larva of D. excentricus, age 23 days. Mating: F3xM1. Diet: Rhodomonas/Dunaliella mixture. 15 April 2016 © Allison J. Gong
Pluteus larva of D. excentricus, age 23 days. Mating: F3xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong
Pluteus larvae of D. excentricus, age 23 days. Mating: F3xM1. Diet: Rhodomonas/Dunaliella mixture. 15 April 2016 © Allison J. Gong
Pluteus larvae of D. excentricus, age 23 days. Mating: F3xM1. Diet: Rhodomonas/Dunaliella mixture.
15 April 2016
© Allison J. Gong

And here’s a short video of that same pair of larvae. They look like they’re singing a duet. If I were the clever sort I’d dub in some music; alas, I’m not that clever. Does somebody want to do this for me?

Sexy time for sea anemones

Posted on by Allison J. Gong

This morning I went out on the first morning low tide of the season. I was so excited to have the morning lows back that I got to the site early and had to wait for the sun to come up. Awesome thing #1 about early morning low tides: Having the intertidal to myself.

Dawn over Davenport Landing. 9 April 2016 © Allison J. Gong
Dawn over Davenport Landing.
9 April 2016
© Allison J. Gong

The purpose for the trip was to collect some algae for a talk I’m preparing; I’ll be speaking to the docents at Natural Bridges State Beach at their monthly meeting this coming Wednesday. They invited me to talk to them about algae. I already have a lecture on algae prepared, but last year I set the bar pretty high with this particular audience and want do something a little different. So I’ll talk to them for a bit, show them some of my pressings, and invite them to press a couple of specimens. This morning I collected a few pieces of algae and took a bunch of pictures.

The Anthopleura anemones continue to fascinate me. At Davenport Landing there’s an area where the rock has eroded and forms a sort of channel. In this channel at low tide the water comes about up to my knees. The rock in the channel remains clear of algae but sometimes contains sand. Scattered over the bottom of this channel are several A. artemisia anemones, which can burrow into the sand when it is present. I’ve photographed these animals many times, as they are magnificently photogenic and in deep enough water that I can just stick my camera below the surface and click away.

This morning the first anemone I looked at in this channel had some orange gunk on its oral surface. At first I thought it had latched onto a piece of bleached algae, but then noticed that others had the same thing. My second thought was, “Ooh, eggs!” If I were at the lab I’d have sucked up some of the gunk and examined it under the microscope.

Spawning female Anthopleura artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning female Anthopleura artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong

Usually when animals spawn the gametes are quickly dispersed by water currents. But this channel is high enough that at low tide it doesn’t exchange water with the ocean so there are no currents except those generated by the wind. Awesome thing #2 about early morning low tides: No wind. Once I used the camera as a sort of underwater microscope I could see the granular texture of the orange gunk, which told me that these were, indeed, eggs. Cool! Because I was on a hunt for algae I didn’t spend a lot of time censusing these anemones, but I figured that statistically speaking they couldn’t all be females. And sure enough, after a very short search I found some males.

Spawning male A. artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning male A. artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong
Spawning male A. artemisia at Davenport Landing. 9 April 2016 © Allison J. Gong
Spawning male A. artemisia at Davenport Landing.
9 April 2016
© Allison J. Gong

So today I learned that April is when the A. artemisia anemones have sex. Makes sense, as spring is the time of year when many organisms (algae and invertebrates) in the intertidal reproduce. Reproduce sexually, that is.

Some animals reproduce clonally as well as sexually, and while sexual reproduction tends to be seasonal, clonal reproduction doesn’t seem to be. Along the coast of central/northern California we have four species of anemones in the genus Anthopleura:

  • A. artemisia, the moonglow anemone (see above)
  • A. elegantissima, the aggregating anemone
  • A. sola, the sunburst anemone
  • A. xanthogrammica, the giant green anemone

Of these four species, only A. elegantissima clones readily. It does this by ripping its body in half in a process called binary fission. The two halves of the animal pull away from each other and the tissue between them gets stretched thinner and thinner until it rips. Then each former-half heals the wound and gets on with life, completely independent of the other. It sounds rather awful but is a very effective way to form clones of genetically identical units that can monopolize large areas in the intertidal.

Anemone (Anthopleura elegantissima) undergoing binary fission, at Davenport Landing. 9 April 2016 © Allison J. Gong
Anemone (Anthopleura elegantissima) undergoing binary fission, at Davenport Landing.
9 April 2016
© Allison J. Gong

It’ll probably take this anemone another day or two to completely tear itself into two pieces. Anemones can continue to clone like this, with each individual splitting into a pair of individuals, for a long time. Eventually this process can form large clones. More about the ecology of these clones in a separate post some time.

Still on the fast track

Posted on by Allison J. Gong

Because I was so surprised at how quickly my sand dollar larvae (Dendraster excentricus) were developing, I checked my notebook from the invertebrate embryology course I took while in grad school to see if what I’m observing now is normal for these animals. It turns out that yes, Dendraster does develop at a much quicker rate than its cousin the sea urchin. And now that I think of it, when I took that 5-week embryology course the sand dollars were the only echinoids that we followed all the way to competence; we spawned and observed urchins as well, but none of them were as far along as the sand dollars by the time the class ended and we “graduated” our larvae off the dock.

Yesterday my Dendraster larvae were five days old. They already had two well-developed pairs of arms and were working on the third pair.

Pluteus larva of the sand dollar Dendraster excentricus, age 5 days. 28 March 2016 © Allison J. Gong
Pluteus larva of the sand dollar Dendraster excentricus, age 5 days.
28 March 2016
© Allison J. Gong

These larvae are big, too–500 µm long. Of course, they started from eggs that were over twice the size of urchin eggs, but they’ve still grown a lot in only five days. The fourth pair of arms will be the preoral arms. At the rate these larvae are developing, I wouldn’t be surprised if these arms show up in the next few days.

As beautiful as those long arms are, they may be a little too long. The larvae swim and gather food using a band of cilia that runs up and down all the arms; the entire body is ciliated, but the ciliated band is the primary locomotory system. I remember the instructor of my embryology course telling us that echinoid plutei will respond to lack of food by growing longer arms, which increases the length of the ciliated band and thus (presumably) the animal’s ability to capture the food that is available. There are two pieces of circumstantial evidence that my larvae may be a little food-deprived: (1) the really long arms; and (2) the lack of visible food cells in the stomachs. In urchin plutei that are feeding well I can see food cells churning away in the stomachs. These Dendraster plutei have beautifully transparent bodies, but I don’t see food in the guts. On they other hand, they are growing, so obviously they are eating. Just in case they are short of food, though, I’ll increase their food ration for the next few days and see how the animals respond.

In the meantime, I continue to be fascinated by the intricacy of the larval skeleton and the complexity of the skeletal rods themselves. Next time I’ll try to take photos of these.

A new obsession

Posted on by Allison J. Gong

This afternoon I met up with Joanna and Amy, who had come to the marine lab with some sand dollars (Dendraster excentricus) to try to spawn. Since sand dollars are in the same taxonomic group (the Echinoidea) as sea urchins, I’d try the same techniques on these animals I’d never spawned before. I did have to modify some things a bit, mostly to account for the difference in body shape between sand dollars and urchins. Urchins are globular, with quite a large internal body volume, while sand dollars are flat. There’s much less space inside a sand dollar for gonads and guts.

Gravid echinoids such as urchins and sand dollars can be pretty easily induced to spawn by injecting their internal body cavity with a solution of KCl. We shot up all eight sand dollars and five of them spawned, two males and three females. One of the males didn’t give enough sperm to be collected, so we didn’t use his gametes. The other male, though, gave us lots of sperm. And they were good sperm, too.

Live sperm of the sand dollar Dendraster excentricus, 400X magnification. 23 March 2016 © Allison J. Gong
Live sperm of the sand dollar Dendraster excentricus, 400X magnification.
23 March 2016
© Allison J. Gong

If you’ve never had a chance to see swimming sperm under a microscope, today is your lucky day!

And the eggs. Wow, sand dollar eggs are freakin’ cool! For one thing, they’re big, ~130 µm in diameter, compared to the 80 µm eggs of the purple urchin Strongylocentrotus purpuratus. Plus, they have a really thick jelly coat that contains red pigment cells; urchin eggs don’t have the pigment cells, either.

Eggs of the sand dollar Dendraster excentricus. 23 March 2016 © Allison J. Gong
Eggs of the sand dollar Dendraster excentricus
23 March 2016
© Allison J. Gong

The eggs themselves were a little lumpy, not as perfectly round as I’m used to seeing with the urchins, but they fertilized just fine. In all three of the crosses, the fertilization rate was 90-95%. Apparently the sperm have no problem digging through the jelly coat to get to the egg surface.

Zygote of D. excentricus. 23 March 2016 © Allison J. Gong
Zygote of Dendraster excentricus
23 March 2016
© Allison J. Gong

In this photo you can see the familiar fertilization envelope raised off the surface of the egg, as well as the red pigment cells in the jelly coat. This may very well be the most beautiful zygote I’ve ever seen. How many people can say things like that?

After an hour and 20 minutes sitting on my desk at room temperature the zygotes started to cleave:

2-cell embryos of Dendraster excentricus 23 March 2016 © Allison J. Gong
2-cell embryos of Dendraster excentricus
23 March 2016
© Allison J. Gong

The blastomeres are still a little wrinkled and lumpy, but I think they’ll be okay. I’ve poured them into 1000-mL beakers and they’re sitting in one of my seawater tables. Tomorrow afternoon I hope to see them swimming up in the water column. Fingers crossed!

Seeing (wannabe) stars

Posted on by Allison J. Gong

So. I have a batch of larvae from a spontaneous spawning of the leather star, Dermasterias imbricata, that occurred four weeks ago tonight. Until now I’ve never had an opportunity to work with this species, even though we have quite a few of them at the marine lab. I had my own for several years, until they became casualties of the plague about a year into the current sea star wasting syndrome event. In any case, this is the first time I’ve been able to spend time with larvae of this species. At the very least I wanted to see how big they would get and how quickly they would develop, compared to the species I’m more familiar with, Patiria miniata (bat star) and Pisaster ochraceus (ochre star).

When the Dermasterias spawned, the first thing I noticed was that the eggs are huge. I measured them at 220 µm in diameter, which is big even compared to what I’ve seen in other stars. Hatch rates were pretty good, and four days later the larvae were already in the 400-430 µm range. Since I have no experience culturing this species, I thought I’d divvy up my larvae and put them into three feeding treatments to see which larval diet resulted in the best overall success. According to the literature, Dermasterias larvae can be raised on a mixture of the unicellular algae Dunaliella tertiolecta (green) and Isochrysis galbana (golden). My three feeding treatments are: Dun only, a Dun/Iso mix, and Iso only.

A week into the experiment there was a clear difference between the larvae eating only the green food, and those eating either a mixture of green and golden or only the golden. Larvae from all food treatments were about the same size, but the ones eating only Dunaliella had noticeably green guts.

Bipinnaria larva of Dermasterias imbricata. 29 February 2016 © Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on Dunaliella tertiolecta, age 7 days.
29 February 2016
© Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on a mixture of D. tertiolecta and I. galbana. 29 February 2016 © Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on a mixture of Dunaliella tertiolecta and Isochrysis galbana, age 7 days.
29 February 2016
© Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on I. galbana. 29 February 2016 © Allison J. Gong
Bipinnaria larva of Dermasterias imbricata, fed on Isochrysis galbana, age 7 days.
29 February 2016
© Allison J. Gong

Fast forward two weeks, and the larvae were 20 days old. By this time they had progressed from the bipinnaria stage to the brachiolaria stage. The interesting thing was the absence of green pigment in any of the guts, even those that were eating only green food. The D. tertiolecta larvae looked good, actually. They were a little smaller than the other larvae but were perfectly formed.

Brachiolaria larva of Dermasterias imbricata, fed D. tertiolecta, age 20 days. 14 March 2016 © Allison J. Gong
Brachiolaria larva of Dermasterias imbricata, fed D. tertiolecta, age 20 days.
14 March 2016
© Allison J. Gong
Brachiolaria larva of Dermasterias imbricata, fed D. tertiolecta and I. galbana, age 20 days. 14 March 2016 © Allison J. Gong
Brachiolaria larva of Dermasterias imbricata, fed D. tertiolecta and I. galbana, age 20 days.
14 March 2016
© Allison J. Gong
Brachiolaria larvae of Dermasterias imbricata, fed I. galbana, age 20 days. 14 March 2016 © Allison J. Gong
Brachiolaria larvae of Dermasterias imbricata, fed I. galbana, age 20 days.
14 March 2016
© Allison J. Gong

Obviously all of the larvae are assimilating enough of their food to grow and develop normally. I looked at them today but didn’t have time to take pictures. Qualitatively there is no difference between the Dun larvae and the Dun/Iso larvae. In the Iso jars, however, there are many larvae at earlier stages; some are still at the “jellybean” stage. I don’t know if this is because these larvae are developing more slowly, or because of some nonrandom distribution of earlier stages into those jars when I was setting up the feeding treatments.

Next week I’ll measure the larvae again, and will have three data points to track growth trajectories.

Swimming jellybeans

Posted on by Allison J. Gong

When serendipity strikes, I try to go with the flow and ride it as long as I can. The latest wave is my batch of Dermasterias larvae, which are developing nicely for the first four days of life. And now they look just like jellybeans!

They have complete guts now and have already grown a bit, measuring 400-430 µm long. It’s not always easy to catch these guys in the right orientation to take a photo, as they are spinning and swimming through three-dimensional space, but I got lucky:

4-day-old dipleurula larva of Dermasterias imbricata. 26 February 2016 © Allison J. Gong
4-day-old dipleurula larva of Dermasterias imbricata.
26 February 2016
© Allison J. Gong

For now I’ve got the larvae divvied up into different feeding treatments. More on that later.

Serendipity strikes again

Posted on by Allison J. Gong

Actually, it was a fortunately placed phone call from an aquarium curator that struck the other night. I was at home, having eaten dinner and reviewed my lecture for the following morning, when my phone rang. It was the curator, saying that he was making his last rounds of the evening and had noticed that some of his sea stars were spawning. Echinoderm sex–more specifically, the opportunity to collect gametes and observe larval development–always grabs my attention, so I told him I’d throw on some shoes and meet him at the marine lab in five minutes.

Lo and behold, there were leather stars (Dermasterias imbricata) spawning in several of the tanks and seawater tables. Many of the tables were cloudy with sperm, but I found only one female, which seems strange but isn’t so unusual. These spawning events occur in response to some environmental cue, such as day-length, a chemical of some sort, or the phase of the moon. When a sea star (or sea urchin) spawns it also releases chemicals that trigger spawning in nearby conspecifics, as to spawn by oneself is an enormous waste of energy. A single spawning animal can result in all the others of its kind spewing out huge numbers of gametes in an orgy of passive sex. However, an animal can be induced to spawn only if its gonads are ripe. Ripeness depends on the overall health of the animal and requires adequate food; animals that don’t receive enough food don’t have energy to allocate towards gamete production. As eggs are energetically expensive to produce, compared to sperm, it is not unusual for males of a species to mature earlier in the reproductive season than the females. In Washington the spawning season for D. imbricata is April-August. Here in California the reproductive season hasn’t been clearly defined, but I do remember a springtime spontaneous spawning event in the lab several years ago.

Spawning female leather star (Dermasterias imbricata) at Long Marine Lab. 22 February 2016 © Allison J. Gong
Spawning female leather star (Dermasterias imbricata) at Long Marine Lab.
22 February 2016
© Allison J. Gong

That creamy looking mass of goo on the star’s aboral surface is a pile of eggs. Sea star eggs are fairly large, compared to the urchin eggs I’m used to, and sticky. They tend to clump together in stringy globs until they are dispersed by water currents. The star whose arm is photobombing in the lower right corner is a male. He was also spawning copiously and is probably the individual who fertilized most of this female’s eggs.

Given the lateness of the hour and the fact that I had to get up early the next morning I didn’t take many pictures of the eggs, although I did look at them to make sure they were fertilized. They were, so I put them into a 1000-mL beaker of seawater and let them do their thing.

Fast forward to today, about a day and a half after fertilization. About two-thirds of the embryos had hatched and were swimming in the water column. Here’s what they look like under the dissecting scope:

I poured off the swimmers into jars and set them up on the paddle table. I gave them a little bit of food, in case their mouths break through before I can get back to the lab tomorrow afternoon. In the meantime, I took a sample of embryos and examined them under the microscope. They look really cool!

Almost-two-day-old embryo of Dermasterias imbricata. 24 February 2016 © Allison J. Gong
Almost-two-day-old embryo of Dermasterias imbricata.
24 February 2016
© Allison J. Gong

The embryos are almost spherical, measuring 290 µm long and 270 µm wide. They are ciliated all over and swim with the rounded end forward. The flattened end is where the process of gastrulation started. That visible invagination begins at a section of the embryo called the blastopore; the channel is the archenteron, the first gut of the larva. In echinoderms, as in chordates (including us humans), the blastopore will end up being the larva’s anus; the mouth breaks through later at the other end of the archenteron. This is why I don’t need to start feeding the larvae right away even though their gut has begun forming.

Tomorrow afternoon I’ll have a brief window of time when I can check on the larvae and see how they’re doing. I think they may have complete guts by then!

All anemones, all the time

Posted on by Allison J. Gong

While much of America was glued to the television watching a football game, I went out to the intertidal at Davenport Landing to do some collecting and escape from Super Bowl mania. The Seymour Center and I have a standing agreement that some animals–small hermit crabs and certain turban snails, for example–are always welcome, which gave me an excuse to look for them. I also needed to pick up some algae for labs that I’m teaching later this week, so it was an easy decision to be alone in nature for a couple of hours.

As usual, I was easily distracted by the animals, especially the anemones. They are simply the most photogenic animals in the rocky intertidal. And we have an abundance of beautiful anemones in our region; I feel very lucky to photograph them where they live. I would like to share them with you.

First up, Anthopleura sola:

Anthopleura sola 7 February 2016 © Allison J. Gong
Anthopleura sola specimen #1
7 February 2016
© Allison J. Gong
Anthopleura sola 7 February 2016 © Allison J. Gong
Anthopleura sola specimen #2
7 February 2016
© Allison J. Gong

Second species, Anthopleura xanthogrammica:

Anthopleura xanthogrammica 7 February 2016 © Allison J. Gong
Anthopleura xanthogrammica
7 February 2016
© Allison J. Gong
One large and one small Anthopleura xanthogrammica 7 February 2016 © Allison J. Gong
One large and one small Anthopleura xanthogrammica
7 February 2016
© Allison J. Gong

Along the central California coast we have four species of anemones in the genus Anthopleura. Two of them, A. xanthogrammica and A. sola, are large and solitary; in other words, they do not clone. The geographic ranges of these two species overlap in central California. Anthopleura xanthogrammica has a more northern distribution, from Alaska down to southern California, while A. sola typically lives from central California into Mexico.

I’ve seen these congeneric anemones living side-by-side in tidepools at Natural Bridges and at Davenport. Here is a photograph from yesterday. The animals are almost exactly the same size, and are separated by about 30 cm. Can you tell which is which?

So, which is which? 7 February 2016 © Allison J. Gong
So, which is which?
7 February 2016
© Allison J. Gong

The pièce de résistance yesterday was a treasure trove of Anthopleura artemisia anemones. I’d seen and photographed them several times before, and always appreciated the variety of colors they come in. For some reason, though, yesterday they really caught my eye. I had a number of “Wow!” moments.

Anthopleura artemisia specimen #1. 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #1.
7 February 2016
© Allison J. Gong
Anthopleura artemisia specimen #2 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #2
7 February 2016
© Allison J. Gong
Anthopleura artemisia specimen #3 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #3
7 February 2016
© Allison J. Gong

Sometimes two colors are combined:

Anthopleura artemisia specimen #4 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #4
7 February 2016
© Allison J. Gong

Stunning, isn’t it?

But this next anemone is unlike any I’ve ever seen before. Get a load of this:

Anthopleura artemisia specimen #5 7 February 2016 © Allison J. Gong
Anthopleura artemisia specimen #5
7 February 2016
© Allison J. Gong

These stark white tentacles are new to me. The anemone measured about 4 cm across. In every other aspect it looks like A. artemisia, and I’m almost entirely certain that’s what it is. It does feel special to me. I will hopefully be able to keep an eye on this individual and see if its colorless tentacles are a temporary or long-term condition. And now that my eye has been primed to see the colors that A. artemisia comes in, I may notice more unusual color morphs.

Progress report

Posted on by Allison J. Gong

My most recent batch of sea urchin larvae continues to do well, having gotten through the dreaded Day 24. I haven’t written about them lately because they’re not doing very differently from the group that I followed last winter/spring. However, I’ve been taking photos of the larvae twice a week and it seems a shame to let them go to waste, so I’ve put together a progression of larval development. As a reminder, the last time I wrote about these larvae they were six days old.

Age 9 days: The larvae had four arms and were growing their skeletal arm rods. Their stomachs, which we keep an eye on because their size can tell us whether or not we’re feeding them enough, were a bit small but not so much so that I worried.

9-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus. 13 November 2015 © Allison J. Gong
9-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus.
13 November 2015
© Allison J. Gong

Age 12 days: The larvae were growing their third pair of arms. Some had just begun growing the fourth pair of arms. Red pigment spots also start appearing all over the body. Some larvae develop lots of red spots, others have very few. Notice that the stomach is slightly pear-shaped; this is normal.

12-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus. 16 November 2015 © Allison J. Gong
Ventral view of a 12-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus.
16 November 2015
© Allison J. Gong

Age 17 days:  This larva doesn’t look appreciably different from the previous one. This photograph, though, is a bit clearer. The stomach has taken on a pink tinge, due to the red color of the food the animal is eating, and the mouth is the large rounded triangular in the in-focus plane. The pair of skeletal arm rods that are in focus are protruding from the ends of the arms, which raises is something to be concerned about. Sometimes the first sign of imminent doom is the shriveling of the arms, so seeing the rods sticking out makes me think “Uh-oh. . .”

Dorsal view of a pluteus larvae of the purple sea urchin, Strongylocentrotus purpuratus. 21 November 2015 © Allison J. Gong
Dorsal view of a pluteus larvae of the purple sea urchin, Strongylocentrotus purpuratus.
21 November 2015
© Allison J. Gong

Age 24 days: This is about the time in larval development when things often start to go wonky. I’ve looked back at my notes from previous spawnings of S. purpuratus, and seven of the 20 cultures that crashed did so in the week between days 20-28 of development. Some of these cultures were doing well right up to the point that they all died. They were literally there one day and gone the next.

Nonetheless, the current batch of larvae continued to do well. The fourth pair of arms were slow to grow but otherwise the larvae look fine. The top larva in the picture below is lying on its back, so you are looking onto the ventral surface. On the left side of the stomach there’s a little upward-facing invagination; this is part of the initial water vascular system forming. Note also that the overall shape of the larvae is changing a bit. They are becoming less pointy and a bit rounder.

Pair of 24-day-old pluteus larvae of the purple sea urchin, Strongylocentrotus purpuratus. 28 November 2015 © Allison J. Gong
Pair of 24-day-old pluteus larvae of the purple sea urchin, Strongylocentrotus purpuratus.
28 November 2015
© Allison J. Gong

Age 30 days:  At this stage the juvenile rudiment is clearly visible. You can see it as a rather nondescript blob of stuff to the left of the gut. The fourth pair of arms have also grown quite a bit but are still considerably shorter than the others. This individual has two bands of cilia, called epaulettes, that encircle the body. These epaulettes will become more conspicuous as the larva approaches competency.

Ventral view of a 30-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus. 4 December 2015 © Allison J. Gong
Ventral view of a 30-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus.
4 December 2015
© Allison J. Gong

Age 33 days: Today I got lucky! The larvae looked good when I changed their water this morning <knock on wood> and although I’m keeping my fingers crossed I have high hopes for these guys. They’re about as big as they’re going to get, measuring 760-800 µm in length. They will get heavier and more opaque as the juvenile rudiment continues to develop.

33-day-old pluteus larvae of the purple sea urchin, Strongylocentrotus purpuratus. 7 December 2015 © Allison J. Gong
33-day-old pluteus larvae of the purple sea urchin, Strongylocentrotus purpuratus.
7 December 2015
© Allison J. Gong

The really cool thing is that one of the larvae landed on the slide exactly as I wanted it to. It happened to fall onto its left side and stayed there, so I was able to focus up and down through the body to get the rudiment into focus.

Left-side view of a 33-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus. 7 December 2015 © Allison J. Gong
Right-side view of a 33-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus.
7 December 2015
© Allison J. Gong

Do you see five small roundish blobs that are evenly spaced around the larger golden circular blob? The large blob is the stomach, seen in side view. Those smaller blobs are tube feet! Don’t believe me? Then take a look at this close-up:

Juvenile rudiment of 33-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus. 7 December 2015 © Allison J. Gong
Juvenile rudiment of 33-day-old pluteus larva of the purple sea urchin, Strongylocentrotus purpuratus.
7 December 2015
© Allison J. Gong

Now if those don’t look like tube feet, then I’ll eat my hat. What’s also noteworthy about this larva is that its epaulette bands are both visible, especially the posterior-most one.

So far, so good. I won’t know how successful larval development is for these guys until they either make it through metamorphosis, or not. In a very real sense, I won’t be able to draw any conclusions about the success of larval development until they either become established as juvenile urchins, or not. One of my graduate advisors inherited a couple of sayings that he passed on to me, as well as to a whole generation of aspiring invertebrate zoologists:

The animal is always right.

and

The life cycle is the organism.

The first is a given, right? The animal knows what it is and what it’s doing, even if we humans have no clue about what’s going on and can’t decide what its name should be.

The second saying might be a little less intuitive. What it means is that, for organisms with a multi-stage life cycle, you have to consider all of the stages if you want to understand them. This is a much more holistic view of biology, and it’s the one that appeals most strongly to me. When I’m thinking as a naturalist, I find my thought process constantly switching between “forest” and “trees” as I seek to understand even a teensy bit of the world around me. While it’s easy to get distracted by all the cool details of organisms, it’s important to step back and ask myself, “What does it all mean? What is the big picture here?” So yeah. Perhaps when (if!) these larvae turn into urchins and I’ve got them feeding on macroalgae in a few months, I’ll be able to say whether or not larval development was successful. If all goes well this larval phase, as all-consuming and fascinating as it is to me, will be only a small part of these animals’ lives.