Sepiadarium austrinum, Southern Bottletail Squid
Figure from Cephalopods: A World Guide (amzn/b&n/abe/pwll), by Mark Norman.
Pharyngula
Evolution, development, and random biological ejaculations from a godless liberal
Cephalopods can inflict a nasty bite. On their underside, at the conjunction of their arms, they have a structure called the beak which does look rather like a bird’s beak, and which can close with enough force to crush shellfish. Many also dribble toxins into the wound that can cause pain, tissue necrosis, and paralysis. They aren’t the best animals to play with.
If you think about it, though, cephalopods don’t have a rigid internal skeleton. How do they get the leverage to move a pair of sharp-edged beaks relative to one another, and what the heck are they doing with a hard beak anyway? There’s a whole paper on the anatomy of just the buccal mass, the complex of beak, muscle, connective tissue, and ganglia that powers the cephalopod bite.
The diagram above shows the early cleavages of the embryo of the scaphopod mollusc, Dentalium. You may notice a few peculiarities: the first cleavage is asymmetric, producing a cell called AB and a larger sister cell, CD. Before the second division, CD makes a large bulge, called a polar lobe, and it almost looks like it’s a three-cell stage—this is called a trefoil embryo, and can look a bit like Mickey Mouse. The second division produces an A, a B, a C, and a D cell, and there’s that polar lobe, about as large as the regular cells, so that it now resembles a 5-cell embryo. What’s going on in these animals?
Maternal effect genes are a special class of genes that have their effect in the reproductive organs of the mutant; they are interesting because the mutant organism may appear phenotypically normal, and it is the progeny that express detectable differences, and they do so whether the progeny have inherited the mutant gene or not. That sounds a little confusing, but it really isn’t that complex. I’ll explain it using one canonical example of a maternal effect gene, bicoid.
I’m sorry, BigDumbChimp, but you’ve been beaten to this discovery: God Hates Shrimp. It’s old news. It’s also wrong in its emphasis. I read Leviticus…
Whatsoever hath no fins nor scales in the waters, that shall be an abomination unto you.
…and what I see is that God hates cephalopods, the bastard.
Anderson RC (2006) Results of the giant Pacific octopus census in Puget Sound, 2000-2005. Tentacle 14:35-36.
This photograph and more are available at Sky and Sea Photography.
Not all the email I get is from cranks and creationist loons. Sometimes I get sincere questions. In today’s edition of “Ask Mr Science Guy!”, Hank Fox asks,
I was thinking recently about the fact that wax collects in one’s ears, and suddenly thought to be amazed that some part of the HUMAN body produces actual WAX. Weird. Like having something like honeybee cells in your ear.
And then I started to think about what sorts of other … exudates the human exterior produces. Mucus, possibly several different types (does the nose itself produce more than one type?). Oils, possibly several different types. That something-or-other that hardens into your fingernails. Saliva, if you wanted to count our frequently-open mouth as sort-of exterior. What else?
To continue a bit of theme, I mentioned that there were some different ways to approach biology, and that old-school systematists with their breadth of knowledge about the diversity of life are getting harder and harder to find. This is something I also bring up in my introductory biology course, where we discuss how biologists do their work, and I mention that one distinction you can find (which is really a continuum and frequently breached) is that there are bench scientists and field scientists, and they differ in multiple ways. Bench scientists tend to be strongly reductionist, tend to focus on one or very few species, and may study just one specific, highly inbred lab strain of a species, and try to minimize environmental variables. Variation is noise that interferes with getting at basic mechanisms. Field scientists, on the other hand, argue that the simplicity of the lab is unrealistic, that the proper study of organisms has to be done in the messy complexity of the real world, and think that variation, rather than being uninteresting noise, is fascinating stuff, the meat and potatoes of evolution. Both points of view have their place, and speaking for all biologists, I think we appreciate the power and necessity of both approaches. The money seems to mostly go to the bench guys, though, which does unfortunately skew the field as a whole.
After the recent struggles trying to keep up with the traffic on this site, you wouldn’t think I’d feel compelled to go trolling for more visitors, but isn’t that the nature of weblogging? The only point to it all is to rack up a bigger score than the next guy, as if we were playing pinball. So what’s a good ploy? As Lauren has cleverly pointed out, sex sells. And while it may be estrogen week, I’m going to buck the trend, since we all know what’s really important for weblog popularity: penises.
