PZ Myers posted Entry 2382 on June 16, 2006 12:44 PM.
Trackback URL: http://www.pandasthumb.org/cgi-bin/mt/mt-tb.fcgi/2377

dentalium_polar_lobe.gif
lobed_embryo_tease.jpg

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?

Continue reading "Polar lobes and trefoil embryos in the Precambrian" (on Pharyngula)

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Comment #106276

Posted by GvlGeologist, FCD on June 17, 2006 9:55 AM (e)

Just for any of you who haven’t read this post on Pharyngula, go take a look. For this geologist, it’s a facinating read.

Comment #106409

Posted by Bruce Thompson GQ on June 18, 2006 11:53 AM (e)

What signaling molecules set up spiral cleavage patterns? How do they differ from those that set up cleavage patterns in bilateral organisms?

As I read this it sounds like a test question, but I really don’t know.

Delta Pi Gamma (Scientia et Fermentum)