Invertebrate zoology at COA

polychaete setae

2010-10-04T14:43:00.008-04:00

A conspicuous characteristic of most polychaetes are the many setae found on each segment. Here’s a photo of a fireworm, which I promised in class. Their setae are extended further from the body when the worm is disturbed so that an agitated worm is covered along each side with bright white tufts of setae. These setae contain a toxin, and just a slight brush up against them causes them to pierce the skin, break off, and cause a most unpleasant burning sensation. Look, but don’t touch.

Setae are definitely worth a close up look if you get a chance to see them under a compound microscope. The setae are formed during development and throughout the life of the adult worm as they break off during use. As larval polychaetes grow, the setae can be easily seen on each new segment.

vroom vroom veligers

2010-10-02T11:41:00.006-04:00

If I were to choose a favorite larval type, it would certainly be the veliger. While photos of these baby mollusks are lovely, their true charm can only be fully appreciated when you see them in motion.

Mollusks pass through an earlier larval stage, the trochophore, which is a larval type also seen in annelids. Although trochophores are cute in their own right, the lively action of the cilia on the margin of the velum and their tiny shells make veligers a special treat to run across in a plankton sample. Even nudibranchs, which lack a shell as adults, pass through a veliger stage.

Veligers have been famously celebrated in verse by Walter Garstang whose “Ballad of the Veliger” not only described the larvae, but also proposed an adaptive explanation for torsion. During development, molluscan larvae undergo a 180-degree twist of the body, which brings the gills and mantle cavity from where they start at the back of the body into position directly over the head. Perhaps, Garstang suggested in his poem, the mantle cavity provides a space for the larval head to retract into when threatened by enemies, which would make post-torsional larvae less vulnerable to predation. Almost six decades later, Pennington and Chia performed a series of feeding experiments and found no evidence to support this hypothesis, as a variety of predators, including hydromedusae, ctenophores, and crab larvae happily gobbled up abalone larvae whether they had undergone torsion yet or not. A complete understanding of the evolution of the gastropod body plan is likely to be rather more complicated than can be captured in verse.

Otter Cliffs field trip

2010-09-23T12:11:00.006-04:00

The class went on a field trip yesterday to my favorite intertidal site on MDI, Otter Cliffs. Everyone saw various species of hydroids and bryozoans in the wild, as well as sponge. The stinkiness of the sponge provided a memorable demonstration of the secondary compounds used by these critters to protect themselves from being eaten. The pungent odor of rotten garlic mingled with gunpowder seems a convincing predator deterrent. We did happily sample the red alga, dulse, for an interesting intertidal snack.

Communicating Science via Film

2010-09-18T11:33:00.005-04:00

I'm currently reading Randy Olson's Don't Be Such a Scientist, hoping to broaden my perspective on effective science communication. The book's subtitle, "talking substance in an age of style," captures what is challenging and aggravating to scientists who encounter resistance to evidence-based, fact-filled explanations about topics such as evolution and climate change.
Dr. Olson, a PhD from Harvard, with a background in evolution and ecology, also has an MFA in fimmaking from USC. He left the narrow arena of peer-reviewed journals and significantly expanded the audience he reaches through his website and films. Next week, he'll be at the University of Maine at Orono for three days, where panel discussions will follow screenings of several of his films, including Flock of Dodos: The Evolution-Intelligent Design Circus, Salt of the Earth: A Journey into the Heart of Maine Lobster Fishermen, and the improbably titled, Sizzle: A Global Warming Comedy. I'm heading up Thursday for Sizzle, leaving the COA campus at 2:30. Students, let me know if you'd like a ride.
He's come a long way as a filmmaker, but Randy Olson's early short, Barnacles Tell No Lies, is still an excellent illustration of the contrast between the accurate, thorough, and fact-filled, yet ultimately unilluminating approach of a college lecture (however unfairly stereotyped) and the power of humor and compelling visuals that film is so good at.

sponges: simply splendid

2010-09-12T15:39:00.006-04:00

Sponges are typically described as the simplest of animals. In some ways, that’s a fair label. Their bodies are composed of only a handful of cell types responsible for all the functions in a living sponge: covering the outside, pumping water through the inside, digesting food, making the skeleton (yes, sponges have skeletons), and making gametes. These processes are all conducted at the cellular level, with no higher organization imposed. In contrast, there are hundreds of unique types of cells in humans, which are arranged into tissues, organs, and systems.
But sponges should not be underestimated; they have some special attributes.
Archaeocytes, a cell type that is dispersed throughout the body of the sponge, are totipotent, meaning they retain the ability to give rise to any type of cell in the sponge. Totipotency is the quality that makes human embryonic stem cells so attractive as a research tool and as a potential therapy for patients with certain types of cell damage due to disease or injury. Actually, embryonic stem cells cannot make the extra-embryonic membranes or placenta, so they are not, strictly speaking, totipotent, and are more precisely defined as pleuripotent. Virtually all animals begin life as a single, totipotent cell, the fertilized egg or zygote. (There are some exceptions to this assertion; can you think of an example?) During development, cell division and differentiation result in an increase in the number of cells and cell types, with various cell lines specialized for different tasks within the organism. Sponges are likely to be the oldest animals. Thus, the retention of a large population of totipotent cells could be an ancestral trait within our kingdom. Amazing regenerative ability and powers of asexual reproduction, which depend on totipotent or pleuripotent stem cells, are widespread among invertebrates. It’s our bad luck as mammals that our cells that are capable of differentiating into all cells in the body are so elusive, found only very early in development, when the embryo is but a tiny ball of cells.

Phylogenies

2010-09-02T15:15:00.005-04:00

I'm teaching Invertebrate Zoology again this fall, and I intend to blog regularly throughout the term. For starters when I teach this class, before delving into the morphology, physiology, behavior, and ecology of the various groups, I like to think about the larger context and how invertebrates fit into the big picture of life on Earth. One way to visualize this big picture is in a phylogentic tree, which depicts patterns of evolutionary relationships among the groups represented by branches on the tree. This one includes everything from bacteria to people, although it gives short shrift to some important groups, like the Protists, and inflates others. It's odd that the mere 4500 mammalian species take up such a significant proportion of this figure, which represents tens of millions of species, at least. There are fuller treatments of mammalian phylogenic patterns available. Ignoring the bacteria for the moment, this tree of eukaryotes gives a rather different representation of protist diversity relative to the metazoans, which occupy only a modest corner in the lower right of the figure. The textbook for this class presents multiple versions of metazoan phylogeny, and we'll be discussing evolutionary relationships among animal phyla throughout the term.
I love phylogenetic trees and the evolutionary context they offer for considering life's diversity, although there are clearly others who are more committed to this view of the world than I am. This image is from Carl Zimmer's Science Tattoo Emporium, and if you're really excited about scientists acknowledging their passions in ink on their skins, you'll be happy to know there is a book coming out soon.

Bill and TED's malarial adventure

2009-02-11T08:48:00.003-05:00

It's rather old news by now, but I wanted to bring your attention to the events at last week's TED conference. Bill Gates gave a talk that centered largely on education and socioeconomic patterns in the United States. He said plenty about teaching excellence and the impact of talented teachers on their students. He drew a number of conclusions, some I agree with, and some I would argue about. It's a rich subject, with a great deal of controversy, and high very high stakes. However, the headline-stealing event happened early in the talk when he was discussing malaria. As he opened a jar of mosquitoes in the auditorium, he said "there's no reason only poor people should have the experience." In the very next moment he assured the audience that those mosquitoes were not infected with malaria, and no one seemed panicked about contracting a dreaded disease. The only discomfort in the room seemed to stem from the knowledge that the attendees of the conference were part of a privileged society that spent more money on research and medicine for baldness than for malaria. It often seems to me that people who are out "raising awareness" might spend their time more productively "raising money." But Bill Gates has done that and through the Bill and Melinda Gates foundation continues to support work on a range of neglected diseases, including malaria. So I applaud the mosquito stunt. I wish there were an analogous act that could drive home that shameful fact mentioned by Gates in his talk that a poor person in the U.S. is more likely to go to prison than to earn a college degree.

snail tentacles

2009-01-22T12:47:00.003-05:00

As I mentioned in a recent post, ants that are infected with the trematode, Dicrocoelium, are compelled by the presence of the parasite in their brains to march to the top of a blade of grass, bite down, and hang on. This behavior would seem to make it more likely that the fluke will be eaten by a grazing mammal like a cow or sheep, which needs to happen if the parasite is to complete its life cycle. It looks like a fascinating adaptation on the part of the parasite to modify the behavior of its host allowing the parasite to be transmitted more readily to the next host. Ideally, there would be data to document that the parasitized ants are eaten at higher rates than are uninfected ants. But this is not the ideal system in which to gather that kind of data. In fact, even though the manipulation of host behavior by parasites is not considered to be a controversial phenomenon, rigorous studies that are well supported by behavioral data are not as common as you might think. One of the best is Janice Moore's work on birds, pill bugs, and their acanthocephalan parasites, a system I also mentioned earlier. Moore discusses several other examples in her book, Parasites and the Behavior of Animals.
One of the earliest suggestions that parasites might modify the behavior or appearance of their host came from Wesenberg-Lund in 1931. He was studying another trematode, Leucochloridium. In typical trematode fashion, a snail serves as the initial host and a vertebrate, in this case a bird, serves as a final host. There is no arthropod (no insect or crustacean) anywhere in the life cycle, which is a challenge for the parasite, as the bird prefers insect prey and doesn't typically eat snails. To get itself from the snail into the bird, so the story goes, the fluke moves into the snail's tentacles, making them look like colorful, wiggly, and oh-so-tasty caterpillars, which the bird happily gobbles up, thus infecting itself. Alas, experimental confirmation of this tale is lacking. There haven't even been any reports of natural occurrence of predation by birds of these parasitized snails in the wild. But the behavior is pretty cool anyway, and you can be the judge regarding its adaptive significance and consider what sort of evidence would convince you that the parasite is modifying the snail host so that transmission to the bird is improved. As my father, my initial teacher in skeptical thinking, would say, "interesting if true."

California dreaming

2008-12-22T13:04:00.003-05:00

I was supposed to fly out to visit family in California for the holidays, but the nor-easter that blew through Sunday has adjusted our schedule rather dramatically. Our flight's been postponed 5 days. On the bright side, I love the white Christmas in Maine. It's also Nina's birthday, and Isaac Newton's, too, so there's much to celebrate. Unfortunately, my husband traveled a few days earlier to spend extra time with his mom and to work on a paper with a colleague in San Diego, so he's already been out there for some time. I keep reminding myself that we spent the first year of our marriage on separate coasts, while I was finishing grad school and he was starting up at COA. This helps put one Christmas 22 years later into perspective.

ant brains

2008-12-19T12:04:00.003-05:00

Winter break and holiday plans aside, I'm already thinking about the parasites tutorial I'll be teaching next term. Carl Zimmer's book, Parasite Rex, makes the case very persuasively: parasites are so much more than grotesque little footnotes in life's pageant. They are major players in the ecology and evolution of many species. Of course, in addition to their ecological and evolutionary heft, many of them exhibit some really weird and creepy lifestyles. One of the most disturbing tricks that some parasites have developed is that of mind control. An infected host's behavior is altered by the parasite in a way that increases the ability of the parasite to complete its lifecycle. In many cases, parasites gain access to the final host, where reproduction occurs, by first infecting an intermediate host that is later eaten by the final host. Any behavior by the intermediate host that makes it more likely to be eaten benefits the parasite (but not the intermediate host, of course). Some parasites are able to manipulate theirs hosts, actually causing them to engage in reckless behavior. Pill bugs harboring acanthocephalan parasites may spend more time in dryer places and even prefer walking around on whiter surfaces. This may not sound like especially exciting risky behavior, but compared to the safety of the dark, moist leaf litter, where healthy pill bugs prefer to be, the infected pill bugs are more easily seen by birds, which gobble up the pill bugs and serve as the final host of their parasites.
Mind control of ants by liver fluke parasites has been colorfully presented in this video.

Endangered Marine Invertebrate

2008-12-04T12:28:00.004-05:00

A physicist friend recently sent me a link to 20 strange and exotic endangered species, saying that the list was "sufficiently yucky and biological" to appeal to me, and it got me thinking about endangered marine invertebrates. The white abalone is the only marine invertebrate that's been listed as endangered under the Endangered Species Act. "Only one? Those marine inverts must be in pretty good shape," you might be tempted to surmise. But you're more sophisticated than that, so you probably wouldn't. There is a long list of assaults on marine invertebrate species: habitat loss, overharvesting, invasive species, disease outbreaks, pollution, global climate change, and more. Most marine invertebrates just haven't been studied in sufficient depth to be listed as endangered, and there are only a handful that are considered to be "threatened" or "species of concern," which are lesser categories than "endangered." To read more about threatened and endangered marine species, you can find plenty here.
White abalone have suffered dramatically from overharvesting. Here's the somewhat oversimplified ecological tale: Usually as population size goes down, individuals enjoy enhanced rates of growth and reproduction, because competition between individuals decreases as populations shrink. But there's a limit. When populations get extremely small (and what's extreme will vary with the ecology of each species), individuals may suffer reduced rates of growth and reproduction. If you do better with some neighbors around, the benefits of reduced competition that come with a shrinking population ultimately lead to other challenges, the most obvious being finding a mate. The general phenomenon of individuals doing worse as population size gets even smaller is called the Allee effect. This is what happened to white abalones. Mating in abalones is not a particularly touchy-feely process. Males and females shed gametes directly into the ocean where fertilization and subsequent embryonic and larval development occur. Fertilization cannot happen if spawning partners are too far away from each other; even a few meters can result dilution of gametes that is severe enough to eliminate the possibility of fertilization. Moving adult abalone closer to each other in the field, as well as spawning them in the lab to produce offspring are management measures that are being taken to rescue this species from the threat of extinction. There's plenty to read about regarding sustainable seafood (white abalone clearly not included) at this month's Carnival of the Blue.

hermit crab home improvement

2008-11-26T11:34:00.008-05:00

Among the favorite characters in the touch-tank in the museum at College of the Atlantic are the Acadian hermit crabs. Hermit crabs typically live in empty snail shells, which offer protection for their soft, slightly curved abdomens. There are some exceptions to this pattern: a few hermit crabs have straight abdomens and live in worm tubes; others, like the giant coconut crabs, don't use extra coverings at all during adulthood, relying solely on their chitinous exoskeleton for protection. The large Acadian hermit crabs we see here usually inhabit the old shells of moon snails (Lunatia heros) or ten-ridged whelks (Neptunea decemcostata). An odd thing about these shells is that they are often missing chunks along the margin of the shell opening. Odder still, the hermit crabs hack away these chunks themselves, once they've taken up residence in the shell. Diver Ed has captured this behavior on film, and he has routinely seen them doing it during his tens of thousands of hours underwater. Maybe they're getting the size of their shell JUST right. If they left it any bigger, a larger hermit crab might want it and could easily wrestle it away from the smaller resident. Hermit crabs are certainly known to compete for shells. But if customizing the shell is a way to limit competition from larger hermit crabs, why do we see this phenomenon only among the largest individuals? Do bigger hermit crabs have disproportionately larger and stronger claws, capable of pinching off pieces of shell margin, or do the largest snails have disproportionately thinner shells, making modification possible only for the hermit crabs that inhabit the largest shells? I suspect some size-related pattern, but of course I would suspect that. I'm rather obsessed with size-related patterns; my favorite mathematical expression is the allometric equation.

growing clams

2008-11-19T08:15:00.005-05:00

Here is some additional information about Sarah D's clam monitoring project, that the invertebrate zoology class helped out with last month. The main part of her project involves measuring recruitment rates for soft-shelled clams (Mya arenaria, also known as "steamers" on local menus) as well as understanding what kinds of factors may enhance recruitment. A definition is probably needed here: when a larval clam, which has spent a couple weeks swimming and feeding in the plankton, encounters a suitable site, it will metamorphose from a larva into a juvenile clam, burrow into the sediment and take up residence, thus recruiting into the local population. Clearly, the larval supply will affect recruitment rate, but larval choice also plays a role, and marked preferences for a variety of factors including substrate texture, flow regime, presence of conspecifics, presence of prey, and absence of competitors or predators, have been demonstrated among a wide range of larvae of marine invertebrates. They may be tiny, but those larvae can exercise some sophisticated decision-making. For one of Sarah's treatments, she added adult clams to her site to measure the effects of adult conspecifics on recruitment rate. These adults were not enhancing the local supply of larvae; any offspring they produced would be widely dispersed during their weeks-long larval life in the plankton. But the adults do provide settling larvae with the information that the site can support clams from settlement to adulthood, and might be a good choice. As long as Sarah and her project supervisor, Chris Petersen, were moving clams (they added hundreds of clams to several large treatment plots), they decided to also measure growth rates of the clams. They marked the outer margin of the shell with permanent marker in the spring, when they added the clams to their site, with the help of students from MDI High School. Then, this month, they measured the marked clams that they found while they were monitoring clam density and recruitment rate. I was surprised that the marks persisted for 6 months, even though the method was suggested by Brian Beal, from U Maine Machias, who definitely knows his way around clam flat research. The marking technique works, and growth rates were quite variable, even among clams in the same plot, with some showing obvious, substantial shell growth, and others not changing size at all since spring. There are clearly plenty of future projects there waiting on the clam flat for some curious and energetic students. Climbing into a pair of waders and splooshing around on the mudflat offers its own unique rewards: fingers numbed from sorting through samples in November, the aroma of anaerobic sediment (think rotten eggs), gooey mud covering everything from tools to clothes to data sheets. What's not to love?

isopods...oh so pretty

2008-11-07T12:23:00.011-05:00

Isopods are not generally described as pretty. No worries. Beyond their less-than-obvious beauty, there is plenty to admire about them. This order of crustacean arthropods contains over 4000 described species including the pill bugs; they are the most successful terrestrial crustaceans. However, most isopods are marine, and can be found in habitats from tidepools to the deep sea. They're only cockroach-sized in the tidepools, but the deep sea species are bigger than guinea pigs. Even creepier than the giant deep sea isopods are the isopods that make their living as external parasites of fish. Some will enter the fish's mouth and nibble at the tongue, eventually replacing it altogether. As alarming as this sounds, significant effects on the host fish seem to be minimal. To see more photos of parasitic isopods, and read what Richard Brusca, one of the world's experts on this group has to say about them, go here. If you decide to advertise your newfound excitement about isopods and want a shirt like the one I wore in class today, I ordered it from Questionable Content. It was Miriam at The Oyster's Garter who initially led me there via her post on giant isopods, which is definitely worth checking out; the video is nightmare-inducing.

more soon

2008-11-06T08:31:00.002-05:00

I've been gone too long! I was hit by the double whammy of grading a thick stack of midterms and then faculty retreat, which disrupted the fragile momentum I was developing in posting to this blog. The grading was time-intensive although gratifying (the students did well on the exam and are enthusiastic and articulate about what they're learning), and the faculty retreat was productive. Just when I was thinking about an arthropod post, we had the elections, which left me happily contemplating things other than exoskeletons and appendages for a while. I cheerfully ignored invertebrates for another day, threw caution to the wind, and rode a very pleasant wave of euphoria. Now I'm back.

hot nudibranchs

2008-10-21T12:22:00.003-04:00

As my students recover from turning in their midterms, the various viruses that seem to be sweeping campus, as well as sundry surgeries, I thought this slideshow might prove therapeutic. But don't get so dazzled by those lurid colors and such that you stop thinking altogether. Remember that one of the special things about gastropods is that they exhibit torsion, a 180-degree twist of the visceral mass (including most internal organs and nervous system) relative to the foot. Among many consequences of torsion is the loss of the left post-torsional gonad and displacement of all the pipes that empty into the mantle cavity over to the right, downstream of the gills, which is a better place to dump your urine, feces, and gametes, after all. While nudibranchs and their sea-sluggy opisthobranch kin are detorted (untwisted) as adults, notice they all retain a penis that emerges from the right side. Yes, they ALL have a penis, being simultaneous hermaphrodites, and it's on the right side for all of them. A remnant of torsion past, both ancestrally and developmentally.

Mudflats

2008-10-17T14:26:00.008-04:00

We had a great field trip at Hadley Point this week, where we helped with a student project on clams and collected all manner of worms to look at back in class. More on the worms in a later post. First, we helped Sarah census her baby clams to see if soft-shelled clams, Mya arenaria, exhibit enhanced recruitment in her two treatments (raked and brushed) compared to control plots. Raking roughens the bottom while "brushing," in which small branches of spruce trees are stuck into the mud, provides structure that affects water flow, which may increase the likelihood that clam larvae that are ready to settle out of the plankton encounter the bottom. Using sections of 6 inch PVC pipe to collect core samples, students scooped out the mud and counted all the little clams they found in the sample. I'm hoping Sarah will present her results to the class soon and will also comment here in the blog. Adequate recruitment is only the first step in maintaining a population that's able to be harvested sustainably. Subsequent predation on the baby clams before they reach harvestable size is also an important factor, and some resource managers will seed clam flats with babies from hatcheries or elsewhere, thus ensuring there are plenty of individuals there to start with, and then protect those flats with netting to exclude predators. That's an approach used here on MDI, in Southwest Harbor. Soft-shelled clams are an important component of Maine's fishing industry, although their importance is dwarfed by the commercial lobster fishery. To find out more about Maine's fisheries, including both recreational and commercial, check out the Department of Marine Resources website.

Siboglinidae

2008-10-14T13:38:00.004-04:00

The phylum Annelida, the segmented worms, gets more interesting all the time. In addition to earthworms, leeches, and the marine polychaetes, there have been some recent additions. Creatures such as Riftia, the large, red-tentacled worms that live at hydrothermal vents, once considered to belong in a separate phylum, are now included within the annelids. Morphological and molecular evidence unambiguously supports uniting these vestimentiferans, along with the pogonophorans into a single taxon, the Siboglinidae within the annelids. Most analyses interpret the siboglinids as nesting within the Class Polychaeta, the largest annelidan class.
Even more interesting than their evolutionary relationships is the unusual approach to nutrition employed by some members of this group of worms. Although Riftia is a very large worm, significantly taller than I am, it doesn't eat or have a gut; instead it relies on symbiotic bacteria to fix carbon and generate food from the oxidation of inorganic molecules. The details of the biochemical pathways used in this process are being revealed in spite of the fact that these endosymbiotic bacteria cannot be grown in culture in the lab.

Molluscan Zodiac

2008-10-13T17:48:00.002-04:00

In case the regular zodiac is no longer interesting enough to entertain you as you consult it for "advice," once you know a thing or two about mollusks, this may be a superior alternative. Even though I'm providing this link on my blog, I want to make it perfectly clear to my students that regardless of the form it may take, even molluscan, astrology is bunk. But even this crotchety skeptic is amused to see that her molluscan sign is The Barnacle (which is not actually a mollusk, but more on that another time).

Cephalopod Appreciation and Awareness Day

2008-10-08T13:24:00.005-04:00

I was going to write a post about nudibranchs since we're covering mollusks in class this week, but it's much more timely to mention cephalopods today. October 8 is Cephalopod Appreciation and Awareness Day, and it's a day of celebration. Among the cephalopods, which include octopus, squids, cuttlefish, and nautiluses, the octopuses are most famous for their ability to camouflage themselves. Not only do they have chromatophores in their skin, which are under nervous control and can effect instantaneuos color change, they are able to change the texture of their skin to better match their surroundings as well. In addition to those tricks of color and texture, this Indonesian mimic octopus, only reported in the scientific literature in 1998, changes its behavior, not to match a background, but to mimic other organisms. I'm a bit skeptical about how much of this behavior would be effective as mimicry. However, even though some attempts may look a bit weak, the effectiveness of the flounder mimicry has been pretty well documented. Whether they're actually as adept at mimicking the diversity of models they're been credited for, they are certainly very handsome animals.

Fabulous flatworms

2008-10-03T15:29:00.010-04:00

The phylum Platyhelminthes is so big (a beefy 34,000 species) and so diverse that a single lecture or chapter in an invertebrate zoology text book just can't do them justice. So here's a bit more. First of all, here's a gorgeous, free-living Hawaiian flatworm. Even large flatworms like these typically crawl along the bottom, relying on primarily on ciliary gliding. However, they are also able to swim, relying on exquisite coordination of their muscle layers to generate graceful motion that propels them through the water.

And then there are those parasitic flatworms. Definitely read about the trematode life cycles that can be found in every invertebrate zoology textbook on the shelf: Chinese liver fluke, blood fluke (the cause of schistosomiasis), and the lancet liver fluke, which infects sheep and other ruminants. In this fluke, one of the intermediate hosts, an ant, has its brains addled by the parasite, causing it to crawl to the top of a grass blade, bite down and hang on. This behavior makes it more likely for the infected ant to be eaten by the final host, a sheep, in which the parasite can complete its life cycle.
I also promised my students more information on other trematodes not mentioned in the text book. The lung fluke, Paragonimus westermani, relies on humans and felines as the definitive host. The adult worms live in small capsules embedded deep in the tissue of the host's lungs. The sexually mature worms produce eggs, which are shed through the host's mouth as they are coughed up, or with the host's feces if they are swallowed by the host after being coughed up. Once released into fresh water, the larva hatches and swims to its first intermediate host, a snail. Several cycles of asexual reproduction occur within the snail (sporocyst produces many rediae; each redia produces more rediae or many cercariae). The cercariae leave the snail and penetrate a crab where they encyst in the muscle. To reach sexual maturity, the immature flukes must be ingested by the final host, which preys on the infected crab. If the crab is not thoroughly cooked, and cats never cook their food adequately to kill parasites, the fluke larvae move through the definitive host's gut wall and burrow into the lungs, where they reach sexual maturity. And one last cool micro-fact: this disease was first describe in two Bengal tigers that died in European zoos in 1878, so says Wikipedia.
And if the flukes aren't alarming enough, there are the tapeworms, another class of flatworms, with 3400 species. These are gut parasites of all major vertebrate taxa, and also typically rely on vertebrate or arthropod intermediate hosts. In contrast with the fluke life cycles, the larval stages of the tapeworms are usually passive, and transmission to the next host relies on the intermediate host being eaten along with its tapeworm parasites. In the tapeworm that affects your dog, eggs are shed via the anus. The eggs are eaten by larval fleas and as the fleas mature, they are swallowed inadvertantly by the dog in its typically routine of licking, nibbling, and grooming. Once in the dog's gut, the tapeworms grow and produce copious eggs. When the eggs leave the dog, they are released in packets, tiny wriggling bits of the tapeworm itself, called proglottids. Dogs that scoot their bottoms along the floor are responding to the sensation of these eggs packets leaving their bodies.
In the pork tapeworm, Taenia solium, humans are the only definitive host. Eggs are shed with the host's feces and must be ingested by an intermediate host to continue the life cycle. The intermediate host is usually a pig, and the larvae encyst in the pig's muscle. Eating undercooked pork results in the cysts developing into adult worms in the intestines of its host. These worms can be several meters long and produce eggs for many years. This may sound plenty gross, but an even worse problem results if a human rather than a pig serves as an intermediate host by ingesting eggs. If a person infected with an adult tapeworm prepares food without adequately washing his hands, eggs can be ingested by anyone eating that food. Also, autoinfection is possible if someone with a tapeworm infection vomits. I leave the details for the reader to discern. In any case, the eggs also make cysts in the human as an intermediate host, but they are typically found in the lung, liver, eye, or brain, and have severe consequences.
That's enough revolting parasite stories for now. Don't worry, we'll get to nematodes shortly. In the meantime, you can always check out the latest from Carl Zimmer.

Trenton bridge

2008-10-01T10:44:00.005-04:00

Yesterday the inverts class went on a field trip to Trenton bridge. We parked along route 3, which was busy with commuters and tourists leaving the island for the afternoon. After clambering down the steep slope under the bridge, we enjoyed the relative calm as the busy traffic we'd left behind made itself known only as muffled whumps as each car passed overhead.
The class cheerfully explored, looking especially at subtidal critters encrusting the kelps that grow lushly at this site, and we saw colonial tunicates, hydroids, hermit crabs encrusted with "snail fur," and bryozoans. During this trip, I was reminded of many earlier visits to Trenton bridge for various collecting trips in the past.

Here is something I wrote in late November a number of years ago:

A Marine Biologist's Thanksgiving Reflections

One of the highlights of my winter break was harvesting seaweed under the Trenton bridge for a Thanksgiving dinner with family and friends. I'd gotten a recipe for fresh sea vegetable salad out of a cookbook I'd recently bought on a trip to New York where I went to visit my sister, Nancy. I'm not much of a shopper, but New York City always leaves me astonished at the variety of things for sale. It's a dazzling contrast to off-season Bar Harbor. Although I passed up a tempting taxidermy peccary, I did buy my daughter a pair of rubber elf ears for her Halloween constume. Much was available, but I kept my purchases modest. Once home, I continued to ponder the contrasts between the landscapes that my sister and I have chosen for our homes.

I grew up in a competitive family, and although Nancy and I have largely outgrown our desires to best each other, I confess that under the Trenton bridge I indulged briefly in a feeling of superiority. Finally, here was something I had better access to than my cool and groovy urban sister: seaweed. All felt right in the world. I'd had a flicker of the same feeling while still in New York, where my status as seaweed goddess was firmly established one evening over drinks with friends. Along with our martinis, we were served raw oysters resting on a bed of crushed ice and garnished with some brown seaweed, artfully coiled around the dish. Amid the elegance and the sophistication, the scientific name of the seaweed came tumbling, unbidden, from my lips, "Ascophyllum," branding me forever as a hopeless science geek from Maine, a label I am quite happy to embrace.

As I gathered seaweed for the salad back home, my smugness developed into a more generous and expansive sort of happiness. The afternoon was full of rich rewards. There were delicate carpets of hydroids, colonial cousins of sea anemones and jellyfish, which look like dense beds of tiny, nearly microscopic flowers. They blushed a fragile pale orange and pink beneath the water's surface. And happily feasting on them like pigs at a trough were dozens of fancy and flamboyant sea slugs, or nudibranchs, if you prefer their more technical yet also evocative label.

I often collect invertebrates and other marine organisms under the Trenton bridge for COA classes, but I never have been there at this time of the year. Much to my chagrin, most of the algae that I was looking for had already died back; the tender, fleshy bits that are nice to eat won't survive in Maine's frozen intertidal zone over the winter. But there was enough for the modest salad I had envisioned. The species composition of my salad reflected what was seasonally available, rather than the suggestions of the cookbook. As I searched in vain for dulse, one of the tastier and more charismatic of the red algae, my plans shifted as I sampled other things on the spot.

I felt strangely self-conscious out there collecting seaweed as food and happily nibbling along the way. I was imagining the picture I made: an eccentric, middle-aged marine biologist, bending over to peer at unseen objects of interest and popping bits of this and that from the water into her mouth. But really, what could be more Thanksgivingy than harvesting the Earth's bounty to enjoy with loved ones? Even though it felt like I was involved in a somewhat suspect, inappropriate, or at least peculiar activity, I began to let go of embarrassment and revel in the gift that we have in living in this place at this time. We have access to so many simple pleasures to be celebrated. That's what I gave thanks for most heartily on November 25th and what I am grateful for every time I sit down to enjoy food with loved ones.

I don't think it's weird that our family, headed by two atheists, says Grace before a meal. Isn't that what we're all looking for? Find it in food. Find it with family. Find it collecting seaweed at low tide under the Trenton bridge. Find it everywhere you can.

strobiliation

2008-09-26T12:50:00.002-04:00

In the life cycle of Scyphozoans, the medusa is the form that predominates. Nevertheless, scyphozoan life cycles also typically include a polyp form called a scyphistoma. The scyphistoma feeds with a ring of tentacles around the mouth. It undergoes asexual reproduction via transverse fission, and short stacks of genetically identical organisms, which will eventually bud off to become physiologically, anatomically separate individuals, are formed at the oral end of the polyp. The tranversly fissioning polyp is called a strobila. The individuals that bud off to swim freely in the water column are ephyrae, which are baby jellyfish. It is the adult jellyfish that makes gametes and reproduces sexually. A nice series of photos illustrating the life cycle of Aurelia labiata can be seen here. The scyphistoma typically exhibits strobilation only during a certain season. At other times it feeds as any solitary polyp would.

Ptilosarcus

2008-09-25T08:33:00.004-04:00

Even though I said earlier that the jellies were my favorite cnidarians, these magnificent, flamboyant sea pens are also in the running. These are colonial Anthozoans, with a single large polyp specialized to support the colony from a central axis, and tiny feeding polyps dispersed along the margins of each "leaf." As in all members of this subclass (Alcyonaria), the gastrozooids have 8 pinnate tentacles.

These animals get to be over a foot tall and they live with the lower, fleshy part of the central poylp planted in soft sediment. And if their appearance in the bright aquarium lights is not thrilling enough, there's more. These animals can bioluminesce, sending eerie, blue-green waves of light along the colony.

Tunicates

2008-09-24T16:58:00.002-04:00

Thanks to Miriam Goldstein at the Oyster's Garter for writing this delightful post on tunicates; it's entertaining, information-rich, and downright sassy. What more could you want when reading about our closest relatives among the invertebrates?
You mean our closest relatives don't have a face or even a head? If you want to read more about the details that support the assertion that vertebrates and urochordates are sister taxa (and you should), PZ Myers at Pharyngula gives a great explanation about the evidence supplied by developmental genetics. And you can find out what a pharyngula really is; it's more than a blog. There's even a link to his previous post about the Hemichordata, so you can read more about the other non-Echinoderm deuterostome phylum.

Jellies

2008-09-22T16:49:00.005-04:00

The cnidarians exhibit phenomenal diversity within a simple body plan. This phylum includes the sea anemones, corals, sea fans, and hydroids. My definite favorite are the jellies. Claudia Mills, a researcher at Friday Harbor Labs, where I did my graduate work is one of the world's experts on gelatinous zooplankton, which includes familiar, large jellyfish (the scyphozoans), small hydromedusae, large pelagic hydrozoans like the Portuguese Man of War, and comb jellies (ctenophores). The Ctenophora are a separate phylum from the Cnidaria, which include the jellyfish, anemones and corals, as well as the Cubozoa, the scariest class of cnidarians. The sting of all cubozoan species is intensely painful and some are deadly.
Jellyfish blooms are currently in the news, although the causes of population fluctuations are not well understood.
There is a lot of information, some of it conflicting, about what to do if you are stung by a jellyfish. Here is a great place to get the lowdown on the most recent scientific research. They publish an online newsletter every six months that is an annotated bibliography of recent publications on jellyfish stings.

animal phyla

2008-09-12T08:52:00.012-04:00

There are about thirty-something animal phyla that are recognized by invertebrate zoologists. There are two reasons the total number of phyla is imprecise. There is some subjectivity involved in determining whether a clade should be considered a single phylum or whether the group exhibits sufficient diversity to be divided into several. It's the taxonomic argument between the "splitters" and the "lumpers." In addition, new data can increase our understanding of evolutionary relationships. For example, based on new molecular evidence, the vestimentiferans are no longer considered a separate phylum, but are now recognized as a group of highly derived annelids.

There are quite a few phyla that are easily named by non-experts, even if they don't know the scientific names. The Arthropoda is the largest and includes the insects, crustaceans, centipedes, spiders, and scorpions. Echinodermata, Mollusca, and Annelida also include critters familiar to most, as do the Cnidaria and Porifera. There are also various other phyla of worms (flat, round, and others) that are speciose, although less well-known by those who haven't taken an invertebrate zoology class. However, in addition to these groups, which include many large-bodied representatives, there are also quite a few so-called "minor phyla" that contain only a few members. Even though they are not numerically dominant, these groups are important to our understanding of the evolution of organismal diversity. Dave Barry's take on the recently described phylum, Cycliophora, shows that minor phyla can appeal even to humorists.

Figuring out how many phyla there are and who belongs in which phylum is straightforward compared with the task of understanding the evolutionary relationships among phyla. Kenneth Halanych gives a very clear description of our current understanding of the phylogeny of invertebrate phyla. This paper was published in 2004, and there are already minor changes to the tree that I will discuss in future posts.

Nothing in biology…

2008-09-05T14:00:00.003-04:00

During the term, we will be studying animals without backbones. We will be focusing on marine invertebrates and will delve into comparative anatomy, functional morphology, development, ecology, physiology, and behavior. However, it's important to emphasize that nothing in biology makes sense except in the light of evolution. The famous essay by Theodosius Dhobzhansky says it as well as anyone. It beautifully captures the themes of unity and diversity that will underlie our explorations throughout the term.
So this is first and foremost an evolution class.

welcome

2008-09-02T09:33:00.000-04:00

This is the blog for the Invertebrate Zoology class at College of the Atlantic for fall of 2008. I'll be using this as an additional forum to communicate and share information with students currently enrolled in the class, although I welcome readers and comments from all who share an interest in invertebrates. I am Helen Hess, professor for the course and new blogger.