hot nudibranchs

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

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

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

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

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

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

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.