Corals in Maine

Maine is perhaps the only state that's famous for a marine invertebrate.  We even celebrate those lobsters on our license plates.  But recently, Maine has been getting attention for a completely different type of marine invertebrate: our spectacular corals (and here).  If you think of corals only as colonial creatures that make reefs in tropical regions, this news may be surprising.  But several diverse taxa within the phylum Cnidaria are informally referred to as corals.  And some of them live in great abundance in Maine's deep waters.  These include stony corals in the order Scleractinia, which also includes the tropical reef builders.  In addition, there are Alcyonaceans (soft corals and sea fans), and Pennatulaceans (sea pens), with many families represented within each of these orders.  Definitely check out the slide show here; there are gorgeous sea anemones in addition to the abundant gorgonians, which are the stars of the show, comprising the "coral gardens."

Phialella zappai

I told a story in class yesterday about a jellyfish named to honor Frank Zappa.  I think I first heard this story in graduate school in the late 1980s, and it was told to me as a funny little anecdote about the power of invertebrate systematics to bring together a talented musician and an admiring fan, who just happened to be a jellyfish expert.  I had forgotten the name of the genus, but now the entire rich tale has a life on the internet. And there are many examples of other species named after famous (and infamous) folk.  If you are thinking of developing your own expertise in a particular taxon and leveraging your power in giving names to new species you discover as a way to meeting up with your favorite celebrity, you will have to get familiar not only with your organism, but also with rules of taxonomic nomenclature.  What new species, or higher-level taxon (genus, family, order, etc) would you like to be able to name, and what would you name it?

Midterm exam

Chromodoris by David Doubilet

Well done, everyone!  I have a thick stack of exams to grade, and will get a good start on them this weekend.  What follows is a minor rewrite of what I posted at this point in the term last time I taught this class.  As my students recover from turning in their midterms and from the various viruses that seem to be sweeping campus, this slideshow of photos taken by David Doubilet  might be 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.

Bivalves are busier than they look

COA students census clams at Hadley Point

The processes of respiration, feeding, and locomotion in bivalves all rely on the animal moving water through the mantle cavity.  To burrow, bivalves rely on muscle action to squeeze the shells closed, which puts pressure on the blood sinuses in the visceral mass (body) and moves blood into the foot, causing it to extend.  The closing shells also squirt water anteriorly out of the mantle cavity, helping to soften the sediments in front of the burrowing clam, easing their work.  Ed Yong at Not Exactly Rocket Science has a great description of the burrowing process along with photos and links to videos.  The water movement for feeding and respiration is more subtle, and it relies on the action of the cilia that cover the extensive ctenidia (gills) of most bivalves.  Water is swept into the mantle cavity through a larger, ventral incurrent opening at the posterior of the animal.  The oxygen-rich water, laden with food particles, moves anteriorly and dorsally across the ctenidia, which both capture food and extract oxygen from the water current.  The cleared water then passes back posteriorly and out through a smaller dorsal excurrent opening.  You can sometimes see this process in the lab by carefully marking the water near the incurrent opening using food coloring or milk.  You can also visualize water flow through mussels, using the spiffy technique of Schlieren imaging. 

The inspiring Vi Hart

Having just finished my midterm check-in with the class on how the course is going, I’ve been reflecting on my teaching, particularly the lectures for invertebrate zoology.  I like to think my lectures are content-rich and characterized by enthusiasm for the material and that the energy I bring serves as an invitation for students to engage more deeply with the class content.  My speaking style has been influenced by many people, and I am amused to sometimes hear echoes of their voices coming through in my lectures.  Sometimes channeling my inner Diver Ed is a very effective teaching tool.  Vi Hart is someone else whose expertise and exuberance I greatly admire.  I’ll never be able to match her speed of presentation, probably to my students’ relief.  This post was really just an excuse to share these cool videos on hexaflexagons.

tiny camera captures internal view of a starfish eating a mussel

There are some really nice echinoderm videos out there, but this one featured at Deep Sea News is unique.  The beginning of the video is dramatic enough, with an advancing front of starfish creeping up a mussel-encrusted pier piling.  Notice how fluid the starfish look in the time lapse.  Mutable collagenous tissue doing its thing!  Then the predation begins.  The starfish’s stomach should look somewhat familiar if you’ve ever interrupted a feeding starfish.  But seeing it from the perspective inside a mussel shell is a thrilling novelty.  Not really a “mussel’s eye view” as they have no eyes, but still!  As the stomach slides in, you can see the mussel’s gills, the ctenidia, on the right.  The slender, ciliated filaments that make up the gill show up as blurry striations in the foreground.  On the left is the mussel’s mantle, the organ that lays down the shell.  The dark orange gonad can be seen extending into the mantle tissue.  It’s all just starfish food. 

Comb jellies

I always feel like the poor Ctenophora get short-shrift in Invertebrate Zoology, in the mad dash to get through 30+ phyla in a 10-week term.  So for some extra ctenophore wisdom, this is an excellent summary by Claudia Mills.  I knew Claudia from from my days as a UW grad student doing research at Friday HarborLabs.  I have memories of her walking along the FHL dock, scooping up various jellies (hydromedusae as well as ctenophores) using a plastic beaker attached to the end of a long pole.  This is the video I showed in class, in case you want to see it again.  Its awesomeness is marred only by a minor misspelling of the critter's name.  BEROE. 

Even though I spend more time talking about Cnidaria in class than the virtually neglected ctenophores, they’re over far too quickly as well.  For a bit more on a Hydrozoan order that is unusual in entirely lacking a polyp stage, check out this videoabout Narcomedusae by our very own Riley Thompson. 

first field trip of the term

Our field trip yesterday to Otter Cliffs, my favorite intertidal site to explore on MDI, was blessed with gorgeous weather and a good low tide (-1.1 feet).  The goal was to see high diversity of higher taxa, and we focused our attention on phyla and classes, generating a fairly respectable list.

Phylum Porifera, Class Demospongiae

Phylum Cnidaria, Classes Hydrozoa and Anthozoa

Phylum Mollusca, Classes Gastropoda and Bivalvia

Phylum Annelida, Class Polychaeta

Phylum Arthropoda, Classes Insecta and Crustacea

Phylum Bryozoa, Classes Cheilostomata, Ctenostomata

Phylum Echinodermata, Classes Asteroidea, Ophiuroidea, and Echinoidea

Photo of springtails by Adam M

We could have expanded this list by aggressively tracking down flatworms (Platyhelminthes) and ribbonworms (Nemertea), both of which I've seen at Otter Cliffs in the past. As it was, we still had plenty to look at to provide tangible examples of those many branches of the phylogenetic trees that form the underlying conceptual structure for this course. 

The sponge was surprisingly hard to track down!  Virtually everywhere I expected to see it, in tidepools alongside coralline red algae, I found only bare rock.  I don't know what's happened to all the Halichondria that used to be so common there.

My students who are also taking entomology this term were thrilled to find springtails in the upper tidepools.

cladistics

Chiton http://eol.org/pages/586951/overview  

As I said in class on Thursday, phylogenetic trees offer an hypothesis about evolutionary relationships among organisms and provide a context that can help us organize the organismal diversity we encounter.  A tree depicts patterns of shared ancestry, with more closely related organisms sharing a common ancestor more recently.  How are these trees constructed?  They rely on assessing the occurrence of shared, derived characters and rules of parsimony.
Cone snails are united in a single genus, Conus, because they share a number of derived features, most notably, a feeding structure modified as a harpoon, which the largest species can use to kill fish. 
Most snails feed using a radula, which they use for scraping prey off the substrate.  To tell which type of structure is ancestral (exhibited by the common ancestor of all snails), and which type is derived (an evolutionary innovation within snails), compare the feeding structure seen in chitons, which is not a snail, but another class of mollusks.  They have a scraping radula, which suggests that this is the ancestral feeding structure in snails as well.
To construct phylogenetic trees, many characters, including morphological, developmental, and molecular, especially DNA sequence data, are examined. 

Phylum Cycliophora

SEM of Symbion pandora by P. Funch and R.M. Kristensen

The description of a new phylum indicates that the newly discovered organism is different from all known creatures in some very fundamental ways in terms of body plan, development and life cycle.  The Cycliophora were described in 1995, and these microscopic creatures, which make their home on the mouthparts of lobsters, are quite distinctive.  The details of their morphology and life cycle are clearly described in the references from the primary literature listed below and are nicely summarized at the Encyclopedia of Life.  The most compelling presentation of the life cycle of the cycliophorans, which includes sexual and asexual cycles, dwarf males, and various larval forms, is surely this video at CreatureCast.  Check out their full archive for more, and you may find a video created by someone in our current Invertebrate Zoology class.

References:
Funch, P. & R.M. Kristensen, 1995. Cycliophora is a new phylum with affinities to Entoprocta and Ectoprocta.  Nature 378:711-714 doi:10.1038/378711a0
pdf is here
Kristensen, R.M. 2000.  An Introduction to Loricifera, Cycliophora, and Micrognathozoa.  Integrative and Comparative Biology 42:641-651. doi: 10.1093/icb/42.3.641
http://icb.oxfordjournals.org/content/42/3/641.short

animal relationships

There are many ways to envision the relationships among all the animals on the planet, and phylogenetic trees offer a potent visual, as I discussed the last time I taught invertebrate zoology.  For a somewhat different message, you can compare the numbers of described species in various animal groups with the numbers of species known in other kingdoms, as in this drawing.
It's a few years old, but it still delights me as much as it did the first time I saw it described here by Chris Taylor. Even though each drawing is not a taxonomically equivalent group (the protists, plants, and fungi are all kingdoms that warrant a single sketch, while one animal phylum, the Chordata, gets a separate drawing for each of its 5 vertebrate classes), it is an arresting graphic.  Most of the space is taken up by the huge fly and by the bulbous tick in the lower left, which represent the arthropods.  Although we'll be spending plenty of time on crustaceans in class, a group oddly neglected in this drawing, I'll be leaving those terrestrial arthropods alone and focusing instead on the marine invertebrates, especially those groups with abundant and diverse local examples.

Invertebrate pancakes

For those who enjoy pondering invertebrates over breakfast, check this out.  And this ambitious cook does much more than inverts.

polychaete setae

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

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

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

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

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

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

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

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."