Tag: marine invertebrates

Spying on filter-feeders

Posted on by Allison J. Gong

Late yesterday afternoon I met my friend Brenna at the harbor to go on a slug hunt. Brenna is working on the taxonomy of a group of nudibranchs for her dissertation, and we’ve gone collecting out in the intertidal together a few times. I knew I’d need some harbor therapy after teaching a microscope class in the afternoon so when she suggested a slug hunt I didn’t have to think twice about saying “Yes!”

I arrived at the harbor before Brenna did, and spent some time lying on the docks taking pictures of the fouling community that lives there. The late summer afternoon light was perfect for picture taking, and I got some great shots.

Mussel (Mytilus sp.) at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Mussel (Mytilus sp.) at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

This is one of my favorites. It’s a view into the posterior end of a live mussel (Mytilus sp.). Mussels live inside a pair of shells and open up only the posterior end to suck in water for respiration and filter feeding. They shut the shells very quickly when disturbed, so I had to sneak up on this individual and take a picture before it knew I was there. Looking through the opening you can see a blurry pale structure running from left to right; I think this is the mussel’s gill. The elaborately fringed dark structure that looks like a pair of curtains extending towards each other is the edge of the mantle. Because most of the mussel’s body is enclosed within the shells, the mantle edge contains most of the animal’s sensory organs. Mantles are exquisitely sensitive to touch, light, and certain chemicals; scallops, another type of bivalve mollusk, often have actual eyes on the mantle edge.

In addition to spying on mussels, I also tried to catch polychaete worms off-guard. There are several different types of tube-dwelling polychaetes living at the harbor. Most of the ones I saw yesterday were serpulids living in meandering calcareous tubes. Like these:

Serpulid polychaete worm at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Two examples of Serpula columbiana, a tube-dwelling polychaete worm, at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Polychaete worm tubes come in many different materials and morphologies. These serpulids live in calcareous tubes that snake over surfaces. Because the tubes are mineralized, they can extend upwards from a surface, too. The worm spends its entire post-larval life in the tube that it secretes, extending only its “head”, visible as a tentacular crown, for filter-feeding. Like the mussels, serpulid polychaetes are very quick to respond to anything they perceive as a threat. Even a mere shadow passing over them can cause a rapid retreat into the tube finalized by sealing off the tube with the trumpet-shaped operculum.

One of the most conspicuous animals at the harbor is an invasive encrusting bryozoan, Watersipora subtorquata. This animal is one of the first to colonize new real estate. Nothing else looks like it, so it is easy to identify.

Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Watersipora grows as a crust on surfaces such as mussel shells and floating docks, but when two colonies meet they use each other as surfaces, forming these curling sheets. The faint fuzziness that you see sort of hovering above the surface of the sheets is due to the lophophores extending from the zooids. Here’s a closer shot:

Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Watersipora subtorquata, an introduced bryozoan at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

Another of the common introduced species at the harbor is the colonial sea squirt Botrylloides violaceus. This animal comes in a wide range of oranges and even purple. Here’s a colony that seems to understand the visual impact of pairing high-contrast colors:

Colony of the colonial sea squirt Botrylloides violaceus growing over mussel shells at the Santa Cruz Yacht Harbor, 29 August 2015. © Allison J. Gong
Colony of the colonial sea squirt Botrylloides violaceus growing over mussel shells at the Santa Cruz Yacht Harbor, 29 August 2015.
© Allison J. Gong

What looks like a mass of pale orange doughnuts is actually a strictly organized colony. Each of the doughnuts is a zooid, and the hole of the doughnut is the incurrent siphon through which the zooid draws water in. Each zooid has its own incurrent siphon. In this photo you can see several larger holes; these are excurrent siphons, shared by several zooids, through which waste water is expelled. It’s difficult to see in the photo, but the excurrent siphons are raised up above the level of the colony, so water that has already been filtered doesn’t get sucked in again. This is exactly the reason that human structures such as smokestacks and chimneys are tall.

Oh, and since you asked, Brenna did indeed find slugs! And she taught me some field characteristics to help me ID slugs that I find. We both got what we needed on our little jaunt to the harbor.

Hanging on

Posted on by Allison J. Gong

Day 3 of wasting in Leptasterias

The saga continues. When I checked on my ailing stars yesterday I saw, as expected, that most of what I had called Leptasterias #1 (the pink star that had ripped itself into pieces the day before) had disintegrated into small piles of mush. There was no sign of life in any of the small fragments so I threw them away. The largest piece, consisting of two adjacent arms attached to what looks like most of the central disc, was still walking around so I kept it. Today I was surprised to see that it hasn’t died yet. In fact, it looks a little better, with both of the arms active and the central disc appearing to be somewhat more contracted and less sloppy.

Remnant of wasting Leptasterias star, 30 August 2015. © Allison J. Gong
Remnant of wasting Leptasterias star, 30 August 2015.
© Allison J. Gong

The two arms appear to be working together, rather than trying to walk away from each other. I think this is a good sign, although it’s too early tell how much longer this fragment of a star will survive.

The star I had designated Leptasterias #2, which had the very large lesion on Friday, had died and dissolved into a mass of amorphous tissue and skeletal ossicles when I looked at it yesterday.

On the other hand, Leptasterias #3, the larger of the two gray stars, seems to be holding its own, or at least not getting any worse. On Day 1 of the outbreak this star had a small fluffy lesion on its aboral surface. Today the wound appears to have grown a bit but its edges look a little cleaner:

Leptasterias star affected by wasting syndrome, 30 August 2015. © Allison J. Gong
Leptasterias star affected by wasting syndrome, 30 August 2015.
© Allison J. Gong

This star was particularly active this morning. I didn’t want to disturb it or give it any incentive to autotomize its arms, so I left it in its screened container to take pictures and video. It was zooming around and acting, for all intents and purposes, like a normal healthy star.

Fingers crossed that this one makes it!

Whiskey Tango Foxtrot

Posted on by Allison J. Gong

Sometimes the only word that will do is a bad word. I generally try not to use a lot of bad language because on the occasions when I do swear I want my f-bombs to really mean something. Late this afternoon I was on my way out of the lab when I made a quick last trip through the wet lab just to make sure everybody would be okay for the night, when out of the corner of my eye I saw a few odd pink bits in one of my screened containers.

This container held three small six-armed stars of the genus Leptasterias. I had collected them earlier this summer with the goal of showing them to my students when we do the echinoderm diversity lab at the end of the semester. Stars in this genus are interesting because their normal arm number is six and they brood their babies instead of broadcasting gametes into the sea to meet, fertilize, and develop on their own. Plus, like all their echinoderm kin, they are pretty animals. Lastly, enamored as I am of oddballs and out-of-the-ordinary things, I am charmed by Leptasterias‘s six arms because most stars have only five.

So when I opened up the screened container and saw that one of my Leptasterias stars had torn itself into pieces, I let fly with a few f-bombs and other choice expletives. I removed the star pieces into a bowl for a better view.

Leptasterias star dismembered due to wasting syndrome, 28 August 2015. © Allison J. Gong
Leptasterias star dismembered due to wasting syndrome, 28 August 2015.
© Allison J. Gong

Seeing a star that had ripped its own arms off is every bit as horrifying when the star has six arms as when it has five. This act of self-mutilation had probably occurred today, as the star looked fine when I checked on it yesterday. All of the pieces were still alive and crawling around:

Actually, if you examined each of the pieces independently and didn’t know that it was only part of a greater whole, you’d think that they were entirely viable. I put these pieces aside in a separate bowl, although honestly I don’t know why. I’m almost certain they’ll be dead when I check on things at the lab tomorrow morning, and even if they aren’t they’ll be decomposing while still sort of alive, which is even worse. I must be a glutton for punishment.

For a while I held out a teensy glimmer of hope that the other two stars might be okay, but that didn’t last long. It took only a glance to see a big aboral lesion on the center of one of them:

Leptasterias star with large aboral lesion, 28 August 2015. © Allison J. Gong
Leptasterias star with large aboral lesion, 28 August 2015.
© Allison J. Gong

Examination under higher magnification shows just how deep and intrusive these lesions are. The body wall is entirely compromised, resulting in the exposure of internal organs to the outside environment.

Lesion on aboral surface of Leptasterias star, 28 August 2015. © Allison J. Gong
Large lesion on aboral surface of Leptasterias star, 28 August 2015.
© Allison J. Gong

It turns out that none of these Leptasterias is unaffected. The third star in my container has a small aboral lesion:

Small aboral lesion on Leptasterias, 28 August 2015. © Allison J. Gong
Small aboral lesion on Leptasterias star, 28 August 2015.
© Allison J. Gong

Whether or not this third individual will survive is up for grabs, but I wouldn’t bet on it. From my experience with wasting syndrome in Pisaster and Pycnopodia, the disorder progresses extremely rapidly once the animal starts showing signs of illness. And all of these animals appeared just fine yesterday. The small pink star is essentially dead already, it just hasn’t realized it yet. The gray star with the large lesion may very well be dead tomorrow, too. The star with the small lesion might still be alive tomorrow, and this is the only one for which I have a bit of hope for survival.

About a week ago the seawater temperature dropped to 16°C for a few days, but then started creeping back up; today it topped out at 19°C. Correlation is not causation, but I do wonder if another spike in the 19-20° range, on top of stress caused by the ongoing period of warm water, is the proverbial straw that broke the camel’s back. These poor stars have gone through hell lately, and there’s no indication that the water will cool off any time soon. I’d throw up my hands and ask, “What’s next?” but I have a sneaking suspicion that I’ll find out soon enough.

Falling in love

Posted on by Allison J. Gong

Today Scott and I gathered all of our tiny Pisaster stars and assigned them to food treatments. We’re not doing a feeding experiment per se but have the goal of getting these juveniles to grow, and to do that we need to figure out what they eat when they’re this small. Nobody knows, or at least we haven’t been able to find any literature on the subject, so we’re trying a shotgun approach and offering them several different items.

One of the food items is the bryozoan Membranipora membranacea, which I wrote about yesterday. Scott picked up some fresh kelp yesterday afternoon and several of the blades were encrusted with Membranipora. We thought these new colonies might be a more appetizing meal for the stars. We knew we’d have to remove any of the Corambe slugs that might be feasting on the bryozoan, so I put a piece under the scope. And. . . whoa. . .

So lively! The bryozoan colony was unbelievably gorgeous. All of the zooids were active and reactive, with lophophores extended and tentacles flicking. This video is taken in real-time. Note how the zooids act independently, but REact as a group. They share enough neural apparatus that stimuli are perceived almost instantaneously by all the zooids in a region.

One of the things I love about colonial and clonal animals is that they upend our preconceived notions of what an individual is. In an animal like a bryozoan, what is the individual? Is it the zooid, possessing its own feeding apparatus that it employs independently from the other zooids to which it is genetically identical? Or is it the colony, consisting of many zooids? And what role does genetic identity play in the definition of individual? How much integration among units is required before they collectively form what we call a body? So many fascinating questions to ponder!

Anyway, Scott had the brilliant idea of gut-loading the bryozoans before feeding them to the stars, so I fetched a couple mL of the green alga Dunaliella tertiolecta that we have growing in pure culture and gave them a few drops, just to see what the zooids would do.

Wow.

This video is also shot in real-time. The zooids are kind of just doing their thing, but when I add the drop of algae about halfway through the video they kick into high gear and go hyper. I didn’t expect such an energetic response.

It is difficult to convey just how mesmerizing these bryozoans are. They are a fantastic example of animals that are completely overlooked even by many biologists because to understand and appreciate them you need to look at them under a microscope. Without magnification they really don’t look like much, just whitish gray crusts growing on kelp blades. But the microscope opens up a view into their lives and shows us how complex and beautiful they are. Sometimes the most amazing and gorgeous things are the ones you can’t see with the naked eye. And that is exactly what I love about them.

The Enemy of the State

Posted on by Allison J. Gong

I came of age, in an academic sense, working as a technician in a lab where the research focused on colonial hydroids. The other tech in the lab, Brenda, and I would get sent out to collect hydroids, then spend another day or so picking the predatory nudibranchs off the colonies. The PI of the lab called nudibranchs “the enemies of the state” and they really did have a way of showing up out of nowhere and then eating a hydroid colony down to nothing. It was rather amazing, actually. Brenda and I would swear we’d picked off all the nudibranchs, and more would show up the next day. This same PI had another saying:  “For every hydroid there’s a nudibranch that lives on it, eats it, and looks just like it.”

Case in point. Today Scott and I were examining not hydroids, but bryozoans, which are a completely unrelated type of colonial animal. We want to see if our tiny juvenile Pisaster stars will eat the bryozoan. It didn’t take long to see this:

The nudibranch Corambe sp. on the encrusting bryozoan Membranipora membranacea. 13 August 2015. © Allison J. Gong
The nudibranch Corambe sp. on the encrusting bryozoan Membranipora membranacea. 13 August 2015.
© Allison J. Gong

A bryozoan colony consists of many units, called zooids, that are connected in some way to form a functioning larger body. The brick-like white structures in the above photo are the zooecia, or “houses” of the bryozoan zooids. The round object near the center of the photo with wavy white lines is the nudibranch Corambe. The white lines on the back of the slug make it blend in very nicely with the bryozoan on which it feeds, and break up the outline of the body to disguise its size; how can you determine how big something is if you can’t see its edges? This slug is probably 2-3 mm long. As with most creatures this size and so effectively cryptic, it is very easy to overlook the slugs and never see them; however, once you have a good search image they become much more conspicuous and you find them everywhere. Search images are great things.

It’s also easier to see something if it’s moving, and it turns out that this slug can move pretty fast:

The voice that you hear is Scott’s.

Corambe lives primarily on Membranipora and eats it. Membranipora responds to this predation by forming spines along the edges of the colony; the spines make it more difficult for the nudibranch to crawl around. This kind of response is called an inducible defense. The same thing occurs when plants begin to produce noxious chemicals after being munched on by an insect herbivore. Scott and I will set up some feeding treatments for our juvenile stars and Membranipora will be one of the courses served, so we were both glad to see that despite all the slugs we picked off there were still lots of viable zooids remaining.

Here’s what a bryozoan is all about. Each zooecium forms the outer casing of one zooid. The zooecium itself is non-living but contains the living part. In Membranipora all of the zooids in the colony are the same, and each one possesses a ciliated tentacular crown called a lophophore. The cilia on the tentacles produce a current that directs food particles to the mouth, which is located at the base of the lophophore. In this video you can see particles moving in the current, and one zooid accidentally sucks in a glom of stuff that is too big. Watch how it tries to get rid of the piece it doesn’t want.

See how the individual tentacles sort of bend and then straighten up? I call that tentacle flicking.

If you spend a couple of hours looking at something through a microscope it’s inevitable that you’ll see something different and new. In one of the bryozoan pieces I saw two little pink blobs in an otherwise empty zooecium. It looked like they were moving, so I zoomed in and saw that they looked like shmoos. “Shmoo” has become my term for any undifferentiated, unsegmented, worm-like thing that I can’t identify. These pink shmoos were definitely moving, and here’s the video to prove it:

That little squeal at the end of the video? That’s me. I was delighted to see that the shmoos have two eyes and turn somersaults. I still have no idea what they are, and I’m totally okay with that. It’s enough to know that they exist.

A star is born!

Posted on by Allison J. Gong

I’m sorry. I had to go there. You didn’t really expect me not to, did you?

The reason, of course, is that today we got our first settled and metamorphosed Pisaster stars! We were doing our normal Monday water change when I noticed a teensy orange speck on the bottom of one of the jars. I used my beat-up old paintbrush to remove the tiny dot to a dish, put it under the dissecting scope, and saw this:

Metamorphosing ochre star (Pisaster ochraceus), age 48 days. 20 July 2015. © Allison J. Gong
Metamorphosing ochre star (Pisaster ochraceus), age 48 days
20 July 2015
© Allison J. Gong

From this picture it’s a little hard to see what’s going on. The entire body has contracted a lot, from a 2.5-mm larva to about 1/4 of the original size as a 600-µm juvenile, and become much more opaque. There are tube feet and spines as well as some remnants of larval body (the soft bits at the bottom of the animal) at this in-between larvenile stage.

Here’s a picture of a fully metamorphosed little star:

Newly metamorphosed ochre star (Pisaster ochraceus), age 48 days. 20 July 2015. © Allison J. Gong
Newly metamorphosed ochre star (Pisaster ochraceus), age 48 days
20 July 2015
© Allison J. Gong

I expect we’ll be seeing more tiny orange dots on the bottoms and sides of the jars in the next several weeks. At some point we will have to figure out what they eat and provide it for them. But at least we know we’re able to get them through the larval phase.

Just for kicks, here are some pictures of where we grow the larvae and how we do the twice-weekly water changes.

Larval culturing paddle table. © Allison J. Gong
Larval culturing paddle table.
© Allison J. Gong
Step 1: We pour the larvae into a filter to concentrate them into a smaller volume of water. Then we can wash or rinse the jar. © Allison J. Gong
Step 1: We pour the larvae into a filter to concentrate them into a smaller volume of water. Then we can wash or rinse the jar.
© Allison J. Gong
Steps 2 and 3: We use a turkey baster to transfer most of the larvae from the filter into a jar of clean water. The final step is to turn the filter over and wash the last larvae into the jar. © Allison J. Gong
Steps 2 and 3: We use a turkey baster to transfer most of the larvae from the filter into a jar of clean water. The final step is to turn the filter over and wash the last larvae into the jar. Then we fill up the jar and resume the stirring.
© Allison J. Gong

An update on other matters:

Today is the six-month birthday of my baby urchins! Six months ago to the day these little guys were zygotes, and six-months-plus-one-day ago their parents were roaming the intertidal. They grow up so fast!

Juvenile sea urchin (Strongylocentrotus purpuratus), age 6 months. 20 July 2015. © Allison J. Gong
Juvenile sea urchin (Strongylocentrotus purpuratus), age 6 months
20 July 2015
© Allison J. Gong

And lastly, that little shmoo-type thing that I found in the plankton yesterday has revealed itself to be. . . an anemone!

One of the things I like best about cnidarians is the beautiful transparency of their bodies. I love how you can see fluid circulating through the tentacles. Gorgeous, isn’t it?

The perfect storm

Posted on by Allison J. Gong

Although the last thing that any of us marine invertebrate biologists want to see again is a wasted sea star, the syndrome has once again been making its presence felt at the marine lab. It has been almost two years since I documented the initial outbreak, and while nobody is convinced that it has entirely run its course, most of us, myself included, had thought that perhaps the first wave had passed. Then, back in March of this year, I saw one of my stars doing this:

Bat star (Patiria miniata) showing severe symptoms of wasting syndrome, 16 March 2015. © Allison J. Gong
Bat star (Patiria miniata) showing severe symptoms of wasting syndrome
16 March 2015
© Allison J. Gong

Those large white blotches on the aboral surface are open wounds, or lesions, through which some of the animal’s innards are protruding. The arm towards the top of the photo has also begun dissolving, literally wasting away into the environment. The lesions eat right through the epidermis, liberating the skeletal ossicles that lie underneath it; I’ve circled two of them on the right side of the photo and there are two more at the bottom.

The discovery of this wasting animal was alarming and for a while I held my breath whenever I check on stars at the lab, but after several weeks of not seeing any additional sick animals I relaxed my guard and concluded the incident was a one-off. So imagine my horror to walk in this morning and see this in one of my tables:

Oral surface of a wasting bat star (Patiria miniata), 17 July 2015. © Allison J. Gong
Oral surface of a wasting bat star (Patiria miniata)
17 July 2015
© Allison J. Gong

Sea stars generally don’t just lie on their aboral surfaces, and this animal was making no attempt to right itself. See how the margin between the arms is a little wavy? That isn’t normal, either, and shows that the animal’s ability to regulate its internal water content has been compromised. And while bat stars routinely scavenge by extruding their stomachs through the mouth and digesting whatever it comes into contact with, they don’t leave the stomach hanging outside the body when they aren’t feeding.

All of which gave me a bad feeling in the pit of my own stomach, which only got worse when I turned the animal over:

Bat star (Patiria miniata) with several small aboral lesions, 17 July 2015. © Allison J. Gong
Bat star (Patiria miniata) with several small aboral lesions
17 July 2015
© Allison J. Gong

The animal appears deflated and has small lesions all over its aboral surface. I was feeling a little deflated myself when I saw this. With stars it can be difficult to determine just how alive (or how dead) an individual is. This one didn’t fall to pieces when I picked it up, which didn’t exactly surprise me because Patiria is less prone to losing its arms via autotomy than the Pisaster species (ochre, short-spined, and jewel stars) and Pycnopodia helianthoides (sunflower star), in whom one of the symptoms of wasting syndrome is a violent ripping off of one’s own arms. I suppose this makes the whole episode marginally less horrific than when I saw my Pisaster stars wasting, or maybe I’ve become jaded.

In any case, I had to decide what to do with this sick star. It was in a table with half a dozen other bat stars, so whatever it was exposed to or was itself exuding has already been spread to the others. I couldn’t leave it there to rot in place, but neither did I want to throw it away if it was still somewhat alive. I turned the animal so it was oral-side-up again and left it alone to see what would happen. If it righted itself I’d assume it was more or less alive and isolate it in a quarantine tank; if it didn’t, then all hope was lost and it could be tossed. When I was ready to leave the lab several hours later, it was in the exact same position. Verdict: dead.

So, why now? I’ve been thinking about this, and here’s what I came up with. The densovirus that has been linked to sea star wasting syndrome is always around in the environment. Like other opportunistic pathogens it doesn’t usually cause a problem until a host organism becomes stressed or compromised. For the past two years we’ve been aware of wasting events up and down the coast, which wiped out the most vulnerable individuals. Animals with resistance, however, were able to survive. The survivors may have been weakened, though, and the mild El Niño of 2014 and the much stronger one we have now in 2015 have resulted in water temperatures much higher than normal. I haven’t plotted the data yet, but in June and July the water temperature has been hovering at 15-16°C, with jumps this week up to 18.5°C over the past couple of days. These warmer temperatures can be very stressful to animals, which may be just what the densovirus needed to “announce [its] presence with authority” (that’s a quote from my favorite baseball movie, Bull Durham). Outbreaks of wasting syndrome are probably caused by a combination of factors: population density of the host animal, presence of the densovirus, overall health of the host, water temperature, water chemistry, and others I haven’t thought of. We are certainly not close to a complete understanding of this phenomenon.

At this point I don’t have many stars left in my collection. I hope I get to keep them.

You are what you eat, part the first

Posted on by Allison J. Gong

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?

Constellations

Posted on by Allison J. Gong

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