My previous contributions to the basic concepts in science collection were on gastrulation and neurulation, so let’s add the next stage, and the one I named the blog after: the pharyngula.
This is the weirdest deep-sea video clip: a crinoid scuttling across the sea floor on its feeding appendages. These are supposed to be sessile creatures, a stalk with a flower-like fringe of many slender arms, but it’s picked itself up and started crawling.
I swear, I’m going to check under my bed just in case they’ve ended up there. That’s almost as improbable.
Way back in the early 19th century, Geoffroy St. Hilaire argued for a radical idea, that vertebrates and most invertebrates were inverted copies of each other. Vertebrates have a dorsal nerve cord and ventral heart, while an insect has a ventral nerve cord and dorsal heart. Could it be that there was a common plan, and that one difference is simply that one is upside down relative to the other? It was an interesting idea, but it didn’t hold up at the time; critics could just enumerate the multitude of differences observable between arthropods and vertebrates and drown out an apparent similarity in a flood of documented differences. Picking out a few superficial similarities and proposing that something just looks like it ought to be so is not a persuasive argument in science.
Something has changed in the almost 200 years since Geoffroy made his suggestion, though: there has been a new flood of molecular data that shows that Geoffroy was right. We’re finding that all animals seem to use the same early molecular signals to define the orientation of the body axis, and that the dorsal-ventral axis is defined by a molecule in the Bmp (Bone Morphogenetic Protein) family. In vertebrates, Bmp is high in concentration along the ventral side of the embryo, opposite the developing nervous system. In arthropods, Bmp (the homolog in insects is called decapentaplegic, or dpp) is high on the dorsal side, which is still opposite the nervous system. At this point, the question of whether the dorsal-ventral axis of the vertebrate and invertebrate body plans have a common origin and whether one is inverted relative to the other has been settled, and the answer is yes.
There are many more photos of adorable creatures of the deep sea at this site.
By the way, did you know that creationists hate cephalopods because they can’t stuff them in a sack and throw them in the water to drown? Also because they’re cute and lovable and beautiful.
Figure from Cephalopods: A World Guide (amzn/b&n/abe/pwll), by Mark Norman.
Brian O’Brien of Gustavus Adolphus College has sent along an important message for those of you who like big flowers that stink of rotting meat—they’ve got one.
Kids underfoot? Are they pestering you for entertainment? Tell them to go look up dinosaurs in Dinobase, and to come back when they’ve got them all memorized. I remember as a kid it was easy to wow the grownups by memorizing a few dozen genera, but now … whoa. There’s more minutia there than you’ll find in packs of baseball cards, that’s for sure.
I’ve been looking forward to seeing these little jewels in print since I saw Kuratani talk about them at the SICB meetings in January. Hagfish are wonderfully slimy jawless chordates that have been difficult to raise in the lab—although if you poke a whale corpse rotting in the cold deeps you’ll find them swarming everywhere. The Kuratani lab has managed to keep animals of the species Eptatretus burgeri alive and healthy in a lab aquarium maintained at cold temperatures (16°C), and has even had success in breeding them. That object to the right is a single hagfish egg, brown and leathery-shelled and surprisingly big—it’s an inch and a half long!
They collected 92 eggs, and then another limitation emerged: it took 5-7 months for embryos to develop in a small number of the eggs. Hagfish aren’t going to be your typical fast-developing model system, I’m afraid, but they are extraordinarily cool animals, and it’s good to see work beginning on them.
