Every once in a while some random person drops off a creature at the marine lab. Sometimes the creature is a goldfish that had been a take-home prize at a wedding over the weekend (now weddings taking place at the Seymour Center are not allowed to include live animals in centerpieces). Once it was a spiny lobster that spent the long drive up from the Channel Islands in a cooler, and became the Exhibit Hall favorite, Fluffy. This time the objects had been collected off the beach and brought in by somebody who thought they might still be alive.
These white objects are egg masses of the California market squid, Doryteuthis opalescens, that had been cast onto the beach at Davenport. Sometimes the masses are called fingers or candles, because they're about finger-sized. Each contains dozens of large eggs. Squids, like all cephalopods, are copulators, and after mating the female deposits a few of these fingers onto the sea floor. Many females will lay their eggs in the same spot, so the eggs in this photo represent the reproductive output of several individuals. The cephalopods as a group are semelparous, meaning that they reproduce only once at the end of their natural life; salmons are also semelparous. After mating, the squids die. Not coincidentally, the squid fishing season is open right now, the idea being that as long as the squids have reproduced before being caught in seines, little harm is done to the population. Most of the time the squids are dispersed throughout the ocean, and the only time it is feasible to catch them in large numbers is when they gather to mate.
These egg masses look vulnerable, but they're very well protected. The outer coating is tough and leathery, and the eggs must taste bad because nothing eats them. I've fed them to anemones, which will eat just about anything, and they were spat out immediately.
The eggs were brought to the Seymour Center because the person who brought them in thought they might make a good exhibit. I happened to be there that day and got permission to take a small subset of the bunch so I could keep an eye on them. And they did and still do make a good exhibit.
16 April 2018: I obtain squid eggs!
At this stage it is impossible to tell whether or not the eggs are alive. The only thing to do was wait and see.
30 April 2018: After waiting two weeks with apparently no change, I decided it was time to look at the egg fingers more closely again. Lo and behold, they are indeed alive! Look at the pink spots in the individual eggs--those are eyes. And if you can see the smaller pink spots, those are chromatophores, the 'color bodies' in the squids' skin that allow them to perform their remarkable color changes.
9 May 2018: A week and a half later, the embryos definitely look more like squids! Their eyes and chromatophores have darkened to black now. The embryos are also more active, swimming around inside their egg capsules. You can see the alternating contraction and relaxation of the mantle, which irrigates the gills. Squids have two gills. More on that below.
At this point the squid fingers began to disintegrate and look ragged. They became flaccid and lightly fouled with sediment.
14 May 2018 (today): Almost a month after they arrived, my squid eggs look like they're going to hatch soon! I didn't see any chromatophore flashing, though.
In the meantime, some of the eggs on exhibit in the Seymour Center have already started hatching. The first hatchlings appeared on Friday 11 May 2018. The hatchlings of cephalopods are called paralarvae; they aren't true larvae in the sense that instead of having to metamorphose into the adult form, they are miniature versions of their parents.
Peter, the aquarium curator at the Seymour Center, allowed me to take a few of the paralarvae in his exhibit and look at them under the scope. The squidlets are about 3mm long and swim around quite vigorously. Trying to suck them up in a turkey baster was more difficult than I anticipated. But I prevailed!
You can actually see more of what's going on in a video:
The cup-shaped layer of muscular tissue that surrounds the squid's innards is the mantle. When you eat a calamari steak, you are eating the mantle of a large squid.The space enclosed by the mantle is called the mantle cavity. Because the paralarvae are transparent you can see the internal organs. Each of those featherlike structures is a ctenidium, which is the term for a mollusk's gill. The ventilating motions of the mantle flush water in and out of the mantle cavity, ensuring that the gill is always surrounded by clean water.
And now we get to the hearts of the matter. At the base of each gill is a small pulsating structure called a branchial heart ('branch' = Gk: 'gill'). It performs the same function as the right atrium of our own four-chambered heart; that is, boosting the flow of blood to the gas-exchange structure. So that's two hearts. Between the pair of branchial hearts is the systemic heart, which pumps the oxygenated blood from the gills to the rest of the squid's body. This arrangement of multiple hearts, combined with a closed circulatory system, allows cephalopods to be much more active swimmers and hunters than the rest of their molluscan kin.
I expect that my fingers will hatch very soon. If and when they do, it will be a challenge getting them to eat. I've never tried it myself, and cephalopods are known to be difficult to rear in captivity. But I'm willing to give it a shot!
We humans are accustomed to thinking of sexual function as being both fixed and segregated into bodies that we designate as either Female or Male. And while we, as a species, generally do things this way, in the larger animal kingdom sexual function doesn't always follow these rules. Many animals are monoecious, or hermaphroditic, having both male and female sex organs in the same body. Not only that, but lots of animals change from one sex to the other. As in so many aspects of biology, the way humans do things may be thought of by us as "normal," but it isn't the most interesting way.
Take, for example, the slipper shell Crepidula adunca. This is a small limpet-like creature that lives on the shell of a larger snail. Around here the usual host is a turban snail, either Tegula funebralis or T. brunnea.
There are several species in the genus Crepidula, including C. fornicata, which lives on the Atlantic coast of North America. The species epithet gives an inkling of how reproduction occurs in at least these two species of the genus.
Sometimes C. adunca is found in stacks. I've never seen a stack taller than three individuals, but C. fornicata occurs in stacks of about six. The animal at the bottom of the stack is always the largest, and a given turban snail can play host to more than one stack at a time.
As you might guess, it isn't mere happenstance that these stacks of C. adunca occur. It turns out that this unusual living arrangement is key to both sexual function and eventual reproduction in this species. The individual on the bottom of the stack (i.e., the oldest) is always a female; those at the top of the stack (i.e., the youngest) are males. However, every stack begins with a single individual, and the default sex in newly settled C. adunca is male. An experiment conducted at Friday Harbor in Washington State1 showed the change from male to female began when the snails reached a size of 7 mm, and all animals larger than 10 mm were female. Animals that begin life as male and transform into females are described as protandrous hermaphrodites. How common is this phenomenon? Not uncommon among fishes, actually. Clownfishes in the genus Amphiprion are protandrous. Remember how in the beginning of the moving Finding Nemo, Nemo's mom dies? Well, in real life Nemo's dad would have become his new mom!
In any case, all C. adunca begin adult life as males. If they live long enough to reach about 7 mm in length, they might get to become females. Crepidula adunca's unusual living arrangement also facilitates reproduction. Unlike most limpet-like gastropods, C. adunca isn't a broadcast spawner. Rather, it copulates, as hinted at by the species epithet of its congener C. fornicata. A female slipper shell with a male on her back has a convenient source of sperm with which to fertilize her eggs: the male reaches into her mantle cavity and transfers sperm to her. Given the constraint of copulation, a female cannot mate until she carries at least one male on her back, and a male cannot reproduce unless he settles atop a female. Once the eggs have been fertilized, they develop within the mother's mantle cavity until she pushes them out as little miniatures of herself.
Cool little animals, aren't they? They remind us not to think of ourselves as The Way Things Are Done. We have a lot to learn from creatures that are not like us, and it's stories like these that ensure I will never lose my appreciation and love for the marine invertebrates.
1 Collin, R. 2000. Sex Change, Reproduction, and Development of Crepidula adunca and Crepidula lingulata (Gastropoda: Calyptraeidae). The Veliger 43(l):24-33.
One of the defining characteristics of the Phylum Mollusca is the possession of a shell, which serves both as a protective covering and an exoskeleton. We've all seen snails, and some people may have noticed that snails often withdraw entirely into their shells and even have a little door that they can use to seal up the opening of the shell. That little door is called the operculum. Opercula occur in non-molluscan animals, too, such as some of the tube-dwelling polychaete worms and some of the thecate hydroids. Snail opercula come in lots of different shapes, depending on the aperture of their owner's shell.
Given the enormous morphological diversity within the Mollusca it shouldn't be surprising that their shells vary immensely in prominence and shape. In fact, molluscan shells demonstrate quite beautifully the relationship between form and function. The benthic and most familiar molluscs, the gastropod snails, generally have coiled shells. Notable exceptions to this generality are the marine opisthobranchs (nudibranchs and sea hares) and the terrestrial slugs. And for the most part snail shells look recognizably like snail shells, even though some are plain coils, others may be flattened (e.g., abalones), and still others may be crazily ornamented. Aquatic animals crawl around in water, which helps to support the weight of heavily calcified shells. Terrestrial snails, on the other hand, live in a much less dense medium (air) and have lighter, less calcified shells. The trade-off for a more easily transportable shell is that air is also very drying, and a thinner shell provides less protection from desiccation.
I should state for the record right now that I'm not talking about the many molluscs that don't have shells at all, or that have much reduced shells.
The bivalve molluscs (mussels, clams, oysters, etc.) live inside a pair of shells. They are sedentary animals, living either attached to a hard surface or buried in sand or mud. Not being able to run from predators (although some scallops can swim!), their only defense is the toughness of their shells and the strength of the adductor muscles that hold the shells closed. Most bivalves feed by sucking water into the shells through an incurrent siphon, using their gills to filter food particles from the water, and expelling the water through an excurrent siphon. To do so they must open their shells enough to extend their siphons, or at least expose inhalant and exhalant openings, to the water current surrounding them.
So, snails have one shell and bivalves have two. Some of the most interesting molluscs, in terms of shell morphology, are the chitons. The Polyplacophora (Gk: 'many plate bearer') have a shell that is divided into eight dorsal plates. This makes them immediately distinguishable from just about any other animal.
Chitons live from shallow water to the deep sea, but the majority of species live in the intertidal. This is a high-energy habit characterized by the bashing of waves as the tide rises and falls twice daily. Any organism living here must be able to hang on for dear life or risk being swept away to certain death. Chitons are certainly well equipped to survive in this habitat. They have a low profile, offering minimal resistance to the waves. Rather than stand tall and face the brunt of the wave energy, chitons cling tightly to the rocks and let the waves wash over them.
The chiton's shell, divided into eight articulating plates, gives the animal a much more flexible shell than is found in any other mollusc. This allows them to conform to the topography of the rocks, giving them an even lower profile than, say, a limpet of the same overall shape and size.
While most chitons are pretty sedentary, at least during the low tides when we can see them, some of them can move pretty quickly when they want. So what, exactly, motivates a chiton to run? One species, Stenoplax heathiana, lives on the underside of rocks in the intertidal; it comes out at night to forage on algal films and retreats back under its rock with the dawn. I've seen them at Pistachio Beach, where I turned over rocks and watched them run away from the light. This video is shot in real-time; the chitons are really running fast!
When the eight shell plates are visible it's easy to identify a chiton as a chiton. But not all chitons are quite so obliging with their most chiton-ish characteristic, and one is downright misleading.
Below is Katharina tunicata, one of the largest chitons on our coast. Its shell plates are barely visible, as they are almost entirely covered by the animal's mantle, the layer of tissue that covers the visceral mass and encloses an open space called the mantle cavity in which the gills are located. In chitons, the mantle extends onto the dorsal side of the animal and is called the girdle. Katharina's girdle is smooth and feels like wet leather.
The largest chiton in the world is the gumboot chiton, Cryptochiton stelleri, and it lives on our coast. This beast is about the size of a football, reaching a length of 30 cm or so. It lives mostly in subtidal kelp forests, but can be found in the very low intertidal, which is where I usually see it. At first encounter it's hard to figure out what this animal is. It certainly doesn't look like a chiton.
If anything, it looks like a mostly deflated football, doesn't it? Turning it over to look at the underside doesn't help much, either, although this photo does give an idea of how big the animal can get:
Cryptochiton goes one beyond Katharina and covers its plates entirely. Just looking at the animal you'd have no idea that there are eight plates underneath the tough reddish-brown mantle, but you can feel them if you run your finger along the midline of the dorsum. Living subtidally as it does, Cryptochiton doesn't have the ability to cling tightly to rocks that its intertidal relatives do, and it tends to get washed off its substrate and cast onto the beach during storms. I've never seen one on the beach that wasn't very dead. Once a friend and I were trudging back up the beach after working a low tide, and encountered a dead softball-sized Cryptochiton. I mentioned that it would be nice to have a complete set of shell plates from one of these animals. My friend always carries a knife in her pocket, so we started an impromptu dissection right there on the beach. It didn't take long to learn that the mantle of a gumboot chiton is really tough and difficult to cut through with a pocket knife. And even once we got through the mantle, dissecting the plates from the underlying tissue wasn't going to happen with the tools we had with us. Besides, the stench was godawful even with our unusual tolerance for the smell of dead sea things. We abandoned that corpse.
Many beachcombers have found white butterfly-shaped objects in the sand, but not known what they are. They are definitely calcareous and feel like bone, but what kind of animal makes a bone shaped like this? Turns out this object is one of the shell plates from C. stelleri. They wash up frequently, never attached to their neighbors so they provide no clue as to what organism they came from.
In order to obtain a complete set of Cryptochiton plates, I'd have to start with an intact chiton corpse. I did happen upon another dead Cryptochiton on a beach somewhere I was allowed to collect organisms, and I brought it back to the marine lab. I remember spending a smelly afternoon cutting the plates out of the corpse and removing as much of the tissue as I could, then feeding the plates to various hungry anemones to take care of the rest. Some of the plates got a little broken during the extraction process, but I do have my very own full set!
Some day I will figure out a way to mount those plates permanently.
One final question to ponder. Does a chiton have one shell, or eight shells?
This past Monday I did something rare for me: I returned to the same intertidal site I had visited the previous day. I enjoyed myself so much the first time that I wasn't able to refuse an invitation to go out there again. The site, Pigeon Point, is one of my favorites, especially in all of its spring glory as it is now. It has always been a hotspot especially for macroalgal diversity, and so far this year appears to be living up to its reputation. The day before I collected several reds that I got to spend the next two days trying to identify.
On Monday I was less overwhelmed by obsessed with algae and able to focus more on the animals, and was delighted to find a small cluster of Thylacodes squamigerus, the strange and fascinating vermetid snail. Nearby one of the vermetid snails was a yellow nudibranch (Doriopsilla albopunctata) and one of the common turban snails (Tegula funebralis). The chance proximity of three different gastropods brought to mind the incredible diversity of this group of molluscs.
The Gastropoda are the largest group within the phylum Mollusca, and can claim a fossil record that dates back to the early Cambrian, some 540 million years ago. They have been extremely successful throughout that long time and are the only molluscan group to have established lineages in both freshwater and on land (of the other molluscs, only the bivalves have made it into freshwater, with the remaining groups restricted to the sea). As you might expect, this evolutionary history has given rise to a mind-boggling array of body types and lifestyles. Let's investigate this diversity by taking a closer look at the three gastropods in the photo above.
Gastropod #1 (Thylacodes squamigerus): Very few people, on seeing this animal for the first time, would guess that it's a snail. Most would say that it's a serpulid worm. The tube is calcareous, as it is for serpulid worms, and winds around over rocks in the intertidal.
A close look at the opening of the tube, however, reveals snail-like rather than worm-like features. Thylacodes even has a snail's face, although I'll admit it isn't easy to see if you don't know to look for it. And despite crawling under a ledge with my camera, I didn't get the best view of a face. In this photo, however, you can at least see one of the cephalic tentacles:
Living in a tube cemented onto a rock means that Thylacodes can't go out and find food. It must instead catch food and bring it in. Thylacodes does so by spinning threads of sticky mucus that are splayed out into the water, where they capture plankton and suspended detritus. The threads are then reeled in and everything--mucus and food--is eaten by the snail. Thylacodes tends to occur in groups, and individuals within an aggregation contribute threads to a communal feeding net, which presumably can catch more food than the sum total of all the snails' individual efforts.
Pretty unexpected for a snail, isn't it?
Gastropod #2 (Tegula funebralis): The black turban snail is probably one of the most common and commonly overlooked animals in the intertidal. People don't see them because these snails are, literally, everywhere from the high- down into the mid-intertidal. They are routinely stepped over as visitors rush to the lower intertidal, and ignored again as these same visitors leave the seashore. I love them. I keep them in the lab as portable lawnmowers for the seawater tables. They are incredibly efficient grazers, keeping the algal growth down. Plus, I think they're cute!
If there's such thing as a 'typical' marine snail, T. funebralis may very well be it. This little snail exemplifies several of the traits we use to define the Gastropoda: it lives in a coiled shell, it uses a radula for scraping algal film off rocks (yum!) and is torted. The shell is easy enough to understand, as everyone has seen a snail at some point, even if it was a terrestrial snail. The radula and torsion, however, may take a little explaining.
Many molluscs have a radula, a file-like ribbon of teeth that can be stuck out of the mouth and used for feeding. In gastropods the radula can be a scraping organ (as in Tegula and other herbivores such as limpets), a drill (as in the predatory moon snails, which drill holes into unsuspecting clams and then slurp out their soft gooey bodies), or a poison dart (as in the venomous cone snails). The radula of a grazer such as Tegula bears many transverse rows of sharp teeth, which are regularly replaced in a conveyor belt fashion as they are worn down. This assures that the teeth being used are always nice and sharp. Remember the radula marks made by the owl limpet (Lottia gigantea)?
Those zig-zaggy marks are made by the scraping of the radula as the limpet crawls over her farm. Tegula funebralis makes the same type of pattern in my seawater tables. All of that white territory is area that had been scraped clean of algae in about a day. Tegula is a very industrious little snail! And they're not shy, either. I don't have to wait a day or so for them to get acclimated when I bring the back to the lab. I can move them around from table to table and after a few seconds they poke their heads out and start cruising around. I've learned from watching them over the years that they seem to have an entrained response to the rising and falling of the tides, even after I bring them into the lab. For the first few weeks of captivity, every morning when I first get to the lab I find that several Tegula have climbed up the walls. I think they're crawling up when the tide is high. I really should look at that more carefully. They never go too far, but sometimes they do drop onto the floor and I find them by stepping on them. Fortunately they are hardy creatures and the floor is always wet with seawater so as long as I find them within a day and plunk them back into the table they're fine.
Now on to torsion. Torsion is difficult to explain, but let me try. The word 'torsion' refers to the twisting of the nerve cord and some internal organs that occurs during larval development of gastropods. Here's how it works. Imagine a closed loop, like a long piece of string with the ends tied together. Lay the loop down on a table and it is just a simple loop. Pick up one end of the loop, twist it counterclockwise 180°, and lay it down again. Now you have a figure-8, right? That's not exactly what happens in the living snail, but you get the picture.
Tegula and other snails have an elongated body that is coiled and crammed to fit inside the shell. If you could take Tegula's body and stretch it out without breaking it (impossible to do, BTW), you'd see the figure-8 configuration of the nerve cord. Other internal organs are re-arranged by torsion, too. As a result, both the gill(s) and the anus now open into the mantle cavity which has been relocated over the head. This arrangement is ideal for keeping the gill(s) irrigated, but not so good for hygienic reasons. Fortunately, the mantle cavity itself is angled so that water flows through it in a more-or-less unidirectional manner, passing over the gill before the anus. Tegula and other marine snails undergo torsion while in the larval stage, and remain torted as adults. This is not the case in other gastropods, as we'll see next.
Gastropod #3 (Doriopsilla albopunctata): Everybody loves the nudibranchs, because their brilliant colors make them easy to love. Unlike the oft-undetected Thylacodes squamigerus and the ignored Tegula funebralis, many of the nudibranchs are somewhat easy to spot in the field because of their flamboyance. This is a crappy picture, but you get the point.
Doriopsilla albopunctata is one of several species of yellow dorid nudibranchs lumped together under the common name 'sea lemon'. Instead of the long fingerlike processes (cerata) that adorn the backs of the aeolid nudibranchs such as Hermissenda spp., the dorids have smooth or papillated backs that may be decorated with rings or spots. Dorids also have a set of branchial plumes on the posterior end of the dorsum; the number and color of these gills can often be used to distinguish similar species. Doriopsilla albopunctata has a smooth yellow back with little white spots, hence the species epithet (L: 'albopunctata' = 'white pointed'), and white branchial plumes.
Nudibranchs are gastropods, although in a different group from Thylacodes and Tegula. The marine slugs, of which the nudibranchs are the most commonly encountered, are in a group called the Opisthobranchia, whose name means 'gill on back' and refers equally to the cerata of aeolids and the branchial plume of dorids. In fact, these animals lack the typical molluscan gill that the snails have. They do have a radula, however, and crawl around on a single foot exactly like Tegula does.
An adult nudibranch's body is elongated, unlike the coiled body of Tegula, and has no apparent signs of having undergone torsion. However, examination of larval nudibranchs shows that they do undergo torsion just like any other respectable gastropod. The weird thing is that some time during the transition from pelagic larva to benthic juvenile they de-tort, or untwist their innards so that their internal anatomy matches their external shape. Instead of having to poop on their own heads, nudibranchs have an anus that is sensibly located at the rear (no pun intended) of the body.
Torsion is one of those biological curiosities whose evolutionary origin is shrouded in mystery. How did such anatomical contortions evolve? Why do gastropods, and only gastropods, undergo torsion? And why do some gastropods tort as larvae, only to detort as they become adults? There are scientific hypotheses about the benefits of torsion, particularly to the larval stages, but nobody knows for sure. After all, none of use were there to watch when it happened.
This is just a tiny taste of the diversity of the Gastropoda. I think it's cool to see three such different gastropods in a small spot of the intertidal. And no doubt there were more that I didn't see. That's one of the joys of working in the intertidal: that I so often see things I wasn't even trying to find.
Before Christmas I was invited to speak at one of the monthly public talks hosted by the Seymour Marine Discovery Center. I'm always happy to be asked to speak to students or the public, so my default answer to these requests is "Yes!" Usually for this kind of presentation I get to choose the topic, but this time my name came up because one of the Seymour Center staffers came up with "bees, banana slugs, and bat stars" so that's what I was given to work with. When my brain took hold of this topic and these very disparate animals, the common theme that came to mind was . . . wait for it . . . reproduction. So yes, this is going to be another sex talk.
What this means is that I need to provide some information on the talk and photos so that the Seymour Center can start publicizing the event, which is in March. Banana slugs are still in the mix, and I don't have any pictures of them, so this afternoon I took advantage of a break between storms to go hiking in the forest and look for slugs. I'd been feeling a little cabin fever for the past few days because of the rain and my own recovery from bronchitis which sapped all of my energy, so I was grateful for an excuse to leave my desk and get outside for a bit.
I headed out to the Forest of Nisene Marks State Park, knowing that where there are redwood trees there should also be banana slugs, especially after all the rain we've had recently. You know how when you're looking for something you can't find it, and when you're not looking for it you see them all over the place? That's how this hike began. It turns out that looking for banana slugs under a deadline makes them very hard to find. And I did have a deadline, as I'd promised to have the blurb and photos for my talk ready today.
After about half an hour of slowly meandering along the trails and getting distracted by all the fungi that popped up after the rains, I did see a banana slug:
That is such a gastropod face! Banana slugs are really cool (and ectothermic, too) animals. One of my buddies in grad school kept one for a pet in our office bullpen; we called it Terry, because slugs are hermaphrodites and deserve androgynous names. Terry really liked eating mushrooms and lettuce.
Banana slugs, and all of the terrestrial snails and slugs, are pulmonate ("lung") gastropods. Most of their marine relatives, with whom I spend so much quality time in the lab and in the field, are prosobranch ("gill in front") gastropods. The nudibranchs and sea hares, which are so photogenic and conspicuous, are opisthobranch ("gill on back") gastropods. As these names imply, the prosobranchs and opisthobranchs possess gills (although they are very different kinds of gills) and thus live in water. The pulmonates don't have gills; they live on land and breathe air. [There are aquatic pulmonates, too. Only a few are marine, and most live in fresh water. They have to come to the surface to breathe.]
So, what is the lung of a banana slug? It's actually the mantle cavity, that oh-so-molluscan feature, that in prosobranchs contains the gill(s). In the pulmonates, the mantle cavity is highly vascularized, as you'd expect from any gas-exchange surface, and opens to the outside by a hole called a pneumostome.
Here's the pneumostome of my first banana slug of the afternoon:
The pneumostome is always on the right side of the animal's mantle. You can actually watch it open and close as the slug breathes.
I found a second slug about an hour into the hike.
See? No pneumostome on the left side.
If I'd had the time, I would have put the slugs together to see if they'd mate. It is a sex talk I'm prepping for, after all. Heck, what would be even better would be to find two slugs already in copulo. No such luck today, though. What's good about not finding everything that I was looking for today is that it gives me incentive to keep going out to search for it. And in the meantime, I've got to start studying up on local fungi. I saw so many different kinds of mushrooms today that now I'm motivated to fill in this particular gap in my knowledge. Might as well take advantage of the El Niño rains, right?
That cute little Melibe I found last week is still alive, and still super cute. It lost one of the two large cerata on its back the second day I had it, and I wasn't sure it would be able to survive long without it, but it has hung in there and started growing a replacement. This afternoon it was crawling on the underside of the surface tension in the bowl:
It is extremely difficult photographing transparent animals; this is the best shot I got. You are looking at the animal's ventral surfaces. It is using its elongate foot to stick to the surface, and the rest of the body is suspended from the foot. The oral hood is wide open and you can see the little blue spots at the base of each tentacle.
The best news is that the tiny Melibe has learned how to eat! The first couple of days I offered it live brine shrimp nauplii, and the Melibe didn't seem to like the thrashing of the nauplii. It cowered and shrank instead of trying to eat them. Then it occurred to me to mush up the nauplii first, so they wouldn't be so active. I also thought that the Melibe might be able to eat the mush itself. Aha, success! Except that I wasn't able to capture any video or photos then.
Today, though, the Melibe did this, while I had the camera all set up and ready to go:
Instead of cringing from the nauplii, today the Melibe was actively going after them. In this video it encloses its oral hood around a handful of nauplii and collapses the hood, forcing the nauplii into its mouth. You can actually see the nauplii stop struggling as they are ingested.
I think the Melibe is growing, too. I'll have time to measure it on Monday.
This morning I was doing some routine cleaning of animal-containing dishes at the marine lab when I noticed a little blob of snot on the outside of the bowl I was working on. Normally I just wipe off blobs like that, but something about this one caught my attention in a different way and I paused to take a closer look at it. What I saw made me glad I hadn't given it the old Kim-Wipe™ treatment.
It was this:
This little 3mm blob of cuteness is the tiniest Melibe I've ever seen. Melibe is one of my favorite creatures of all time. It's an entertaining animal that has unfathomable amounts of charm. Unlike most other nudibranchs, which prey on other animals (typically cnidarians, sponges, or bryozoans), Melibe is a filter feeder. It sweeps its large oral hood, visible to the right, through the water to capture plankton. The flat large-ish structures projecting from the animal's back like wings are cerata, of which there will eventually 4-5 pairs when the slug reaches adult size. The cerata function as gas exchange surfaces; they also contain extensions of the digestive system. When a Melibe is mishandled or stressed, it drops cerata, which can then be regenerated.
Melibe is the most animated of slugs. I dropped a few brine shrimp nauplii on this little guy to see if it would be able to catch them. Unfortunately it looked more like the nauplii were ganging up on the Melibe than the other way around. However, I know from experience that even larger Melibe take a while to figure out how to eat brine shrimp.
But isn't that the cutest slug you've ever seen? It has tiny bright blue dots on its body! Those two little flaps on the top surface of the oral hood are rhinophores. I know they look like ears, but they are chemosensory rather than auditory organs.
And look how fast this little nudibranch can crawl! Remember, it's only 3mm long, and it's making pretty good progress getting to the corner of the bowl.
When dislodged from whatever it's crawling on, Melibe can swim. I thought this one would attach itself to the underside of the surface tension, as they often do, but it thrashed for quite a while before sort of accidentally finding the bottom of the dish again.
And do you know what the best thing about Melibe is? It smells like watermelon. I kid you not. If you touch a Melibe, your finger will smell like watermelon Jolly Ranchers. How could an animal possibly be any cooler than that?
. . . clam, right? Yes, except in this case the bivalve is not a clam, but a scallop. I was out at the harbor with Brenna again this morning, looking for molluscs for tomorrow's molluscan diversity lab. Brenna was hunting for slugs, of course, and had drawn up a rope that had been hanging in the water for god knows how long. Neglected ropes like this are the stuff of dreams for people like Brenna and me, as all sorts of animals recruit to and colonize them. Hauling one up is like going on a treasure hunt.
Two of the animals that had attached to the rope were small kelp scallops, Leptopecten latiauratus. The smaller of the two was about the size of my thumbnail and the larger was about 1.5 times that size. Their shell patterns are very beautiful:
But really, you don't get a feel for how much fun these animals are until you watch them. Scallops are the most animated of the marine bivalves. They have eyes and sensory tentacles along the ventral edge of the mantle, and react strongly to stimuli. They can clap their valves together so quickly that they actually swim. I wasn't able to make either of mine swim, but did get to watch them for a while.
The whitish object waving around on the left side of the frame is the scallop's foot. Rock scallops are not permanently attached to surfaces (if they were, they wouldn't be able to swim!) but they do use the foot to stick. If they find a spot they like, they try to wedge the dorsal, hinged area of the shell into a crevice.
Just like you and me, scallops have bilateral symmetry, complete with left and right sides. Unlike you and me, however, their bodies are laterally flattened and entirely enclosed between the left and right shells. The only parts of the body that extend from between the shells are the foot and the sensory structures on the mantle edge. Leptopecten has many long filament-like sensory tentacles, and brilliant blue eyes.
I thought I'd provoke a reaction by passing my finger over the animal and casting a shadow over it. Nada. But then it closed its shells a couple of times for no reason that I could discern. However, as my graduate advisor Todd Newberry used to say, The Animal Is Always Right™, and what doesn't seem like anything to me could very well be a threat to a scallop.
And by the way, I did also collect a few slugs and a chiton for tomorrow's lab. The highlight for me, though, was the scallops. I hope my students are as captivated by these little bivalves as I was!
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:
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 few months ago, a former student invited me to participate in an activity with local Girl Scouts. The Scouts have a camp this weekend at Henry Cowell Redwoods State Park, and this year their theme is "Commotion in the Ocean." The former student, whose name is Thomas, works for the Squids for Kids program run jointly by the Hopkins Marine Station (the marine lab facility of Stanford University) in Pacific Grove and the NOAA Southwest Fisheries lab here in Santa Cruz. Squids for Kids provides Humboldt squids (Dosidicus gigas) to schools and other kid-focused programs around the country, along with instructions on how to dissect the squids and identify their parts. I think the way it worked is that the Girl Scouts applied for squid and Thomas was assigned the event. He invited me to join him because the Scouts thought it would be good for the girls to see a woman doing the dissection and getting all dirty.
Standard disclaimer: I feel very uncomfortable when people ask me to be a role model for girls, boys, women, men, whoever. It makes me feel self-conscious, as though I'm being scrutinized for a certain intangible quality of role-model-ishness and could somehow come up failing, and that I have to be better than I actually am. So I always go into these things with a little apprehension.
The thing about dissecting a Humboldt squid is that you can't go just part of the way into a squid; you have to dive in with both hands and resign yourself to the smell. Humboldts are large animals, compared to the ones I'm used to working with, and are easy to dissect: All you do is make a cut open the mantle and all the internal organs are there to observe.
Problem with just diving into a squid is that once you do, you can't take any more pictures because your hands get all gunked up. This is the only photo I snapped of the morning's activities before things got very smelly. I really didn't want to smell it on me for the next three days so I wore a lab coat and a glove on my left hand, leaving my right hand "clean" so I could drink my tea and keep an eye on the time. Even so, my right hand still has a bit of squid stink after several hours of near-continual dunking in either seawater or hot freshwater. Maybe I'm just imagining that I still smell it.
Experiences like today remind me that I'm not very good with young kids. I am simply not accustomed to dealing with their short attention spans and don't know how to distill an explanation into 25 words or fewer, which is what seems necessary for the youngest Girls Scouts at camp today.
That said, there was one girl I found very intriguing. I don't know her real name but her camp name was Rockcod. She was maybe 9 or 10 years old. She didn't want to touch any part of the squids even though her friends were getting in there and touching the gills, eyeballs, tentacles, and innards. Rockcod told me that her dad does a lot of fishing and she goes with him. They've never caught squids but catch lingcods and various rockfishes, which they take home and eat. Her uncle once caught a yellowfin tuna that was "as big as the table," probably about four feet long.
Despite adamantly not wanting to touch the squids, Rockcod was clearly fascinated by them. She left our station to participate in other activities but kept coming back and asking questions. She wanted to know what all the parts were and really wanted to be around when we opened up the next squid. She asked all the right questions:
How do you know if it's a boy or a girl?
Where is the ink? Can you write with it?
How come two of its arms are so much longer than the others?
Where is the mouth?
A squid has three hearts? No way!
Can you eat it?
What do they eat?
Several of the other girls (and most of their adult chaperones) were a bit squeamish and/or offended by the smell. I heard "Ew, that stinks!" more than a few times. Well, they do stink, there's no getting around it. Still, I'd rather smell an honestly dead squid than one that has been preserved in formaldehyde. And you do get used to the smell after a while. Except that I still catch a whiff of it emanating from somewhere on my body every once in a while. Hopefully it goes away with my next shower.