Animal Form and Function 5: Chelicerates

The chelicerates are likely the most primitive of the extant arthropod groups, and they are the simplest anatomically.  Chelicerates are one of the first groups of animals known to have made the move from water to land, but their dominion over terrestrial ecosystems has not lasted.  Nowadays, the spaces that once belonged to this ancient lineage mostly belong to crustaceans in water and insects (so, different crustaceans) on land.  Still, chelicerates remain a major ecological force, thanks to the multitudinous mites and ticks and the prevalence of spiders and scorpions as insect predators.

And, they are magnificently weird.

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Animal Form and Function 5: Chelicerates
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Animal Form and Function 4: Crustaceans

The arthropods are the only phylum covered in my course that is split over multiple sessions, and with good reason.  Arthropods are a majority of the species known to science.  Parse that carefully: not a majority of invertebrate species.  Not a majority of animal species.  A majority of species, period.

That massive diversity means that arthropods are also impressively different from one another across their various groups, and covering that diversity requires an extended fraction of the lecture course’s time and two entire lab sessions.  Which groups are covered in which sessions changes from year to year, so for this series I’m doing the three “classical” arthropod subphyla–crustaceans, chelicerates, and “atelocerates”–each as their own post.  Today’s topic is crustaceans.

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Animal Form and Function 4: Crustaceans

Animal Form and Function 3: Annelids and Nematodes

After the tour of seashore beauties in the previous chapter, the annelids and nematodes may seem dull.  The very limited array of annelids that most people encounter–mostly just the one–certainly don’t help that impression, and nematodes all look more-or-less alike.  Like any other animal phylum, though, the annelids have a few surprises for us.

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Animal Form and Function 3: Annelids and Nematodes

Animal Form and Function 2: Mollusks

The next big chapter in the course I teach is on the mollusks.  The most visible component of any seashore’s biota, mollusks are an incredibly diverse group of animals.  One could be forgiven for not knowing in advance that snails, clams, and the colossal squid are about as close together on the tree of life as spiders and lobsters, or humans and pipefish.  Mollusks are, in this way, a classic example of adaptive radiation, in which an ancestral body plan somewhat like a very primitive snail was reshaped into widely dissimilar beasts in response to very different selection pressures.

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Animal Form and Function 2: Mollusks

Guest Post: The Right Way To Be Poor

In discussions of poverty, we sometimes neglect to differentiate between types of poor. I don’t mean the contents of one’s wallet, but rather the poverty narratives that we consider excusable (or, sometimes, even laudable) and those that we don’t.
In the beginning, I was one right kind of poor, the kind that even the most solidly middle class people go through when they first leave home. I was a student. Things are different when you’re a student. Having a ‘hungry day’ is a life experience, something that teaches you a valuable life lesson, something that will become a funny story to tell your kids later. Ramen noodles are an inside joke. Student poverty is cute and funny because it’s expected and because it’s temporary.
With some exceptions, students can expect their poverty to end with the completion of their degree. Their poverty, as with their education, is an investment. Once they graduate, they will be able to work full time and their earning potential will be much higher than that of those who did not go through such a hazing.
That’s what many politicians and voters think of when they think of poverty – a hazing ritual that marks the transition of the individual from childhood into stable financial adulthood. We don’t need minimum wage increases, they argue, because the people asking for them are just entitled teens who don’t want to go through the same hardships as everyone else. They resist social change in the same terms that frat boys resist anti-hazing laws.

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Guest Post: The Right Way To Be Poor

Animal Form and Function 1: Cnidarians and Flatworms

I’m a big fan of this sentiment:

 

Being a geek is all about being honest about what you enjoy and not being afraid to demonstrate that affection.  It means never having to play it cool about how much you like something.  It’s basically a license to proudly emote on a somewhat childish level rather than behave like a supposed adult.  Being a geek is extremely liberating.  –Simon Pegg
I try to keep Pegg’s axiom in mind when I’m teaching.  Every winter, I teach the laboratory portion of a course in animal diversity, much of which consists of dissections.  Every week during that course, my students dissect one or more specimens from selected animal phyla and observe without cutting preserved specimens of several more.  Each week comes with a theme, such as convergent evolution, divergent evolution, or metamerism, and ideas such as the state of the body cavity pervade the entire course as well.

Every session of that class where the time is available, I spend the last 15 minutes or so showing videos, still images, and articles about the weirder and more wonderful aspects of the animals within that session.  For many students, classes like these are their one and only encounter with creatures like ragworms and tarantulas.  Augmenting the dry and often harried perspective offered by detailed dissection guides and midterm exams with the novelty and wonder of their living forms is one way that I try to keep this course interesting even for (gasp) pre-medical students who don’t necessarily enter the course brimming with enthusiasm about crayfish and sea stars.

Infectious enthusiasm is the best teaching aid there ever was, and I bring it to my classes even if I have to add my own material to an established course.  This is that material.

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Animal Form and Function 1: Cnidarians and Flatworms