Pycnogonid tagmosis and echoes of the Cambrian


I'm going to introduce you to either a fascinating question or a throbbing headache in evolution, depending on how interested you are in peculiar details of arthropod anatomy (Mrs Tilton may have just perked up, but the rest of you may resume napping). The issue is tagmosis.

The evolutionary foundation for the organization of many animal body plans is segmental—we are made of rings of similar stuff, repeated over and over again along our body length. That's sufficient to make a creature like a tapeworm or a leech (well, almost—leeches have sophisticated specializations), but there are further steps involved in making a fly or a spider or a human. There is an arrangement of positional information along the length of an animal, so one segment can recognize whether it is near the head or the tail, and the acquisition of new patterns of gene expression based on that positional information that cause the development of specialized structures in different segments. That process of specializing segments is called tagmosis. It's how a fly forms mouthparts in head segments, legs and wings in thoracic segments, and no limbs at all in abdominal segments.

The relationships between segments and how they are specialized are key features in identifying patterns of descent in the arthropod clade. An analysis of those elements in an obscure group, the pycnogonids, has uncovered a surprising relationship—they seem to be related to well known Cambrian organism. You'll have to read through to the end to discover what it is.

Continue reading Pycnogonid tagmosis and echoes of the Cambrian (on Pharyngula)


A fascinating headache, indeed.

Here’s something good that might not hurt:

UCSD Study Shows ‘Junk’ DNA Has Evolutionary Importance[…]e/mcjunk.asp

“…these non-coding regions play an important role in maintaining an organism’s genetic integrity. In his study of the genes from the fruit fly Drosophila melanogaster, he discovered that these regions are strongly affected by natural selection, the evolutionary process that preferentially leads to the survival of organisms and genes best adapted to the environment.”

careful, Norman, if Blast sees your post he likely will think it to support his “pant-loading” idea.


Poking holes in the Ignorati’s silly anti-evolutionary arguments is always fun (sometimes, it’s even a Blast, heh heh!), but the real protein on this site is the great rundowns on the latest findings of evolutionary biologists.

Great article, PZ. The Real Deal beats those Pitiful Posturings every time.

yup, i suddenly realize that i should congratulate the contributors more often for many of their unique and substantive posts like this one.

i’ts small wonder they managed an award from Sci Am


Tagmosis! You’re ‘it’!

Bayesian Bouffant Wrote:

Tagmosis! You’re ‘it’!

Maybe that should be: “Tagmosis! What ARE you?” ;-)

About this Entry

This page contains a single entry by PZ Myers published on October 20, 2005 10:44 PM.

Behe Blasted on Peer Review was the previous entry in this blog.

ID rejection in Australia / DI response is the next entry in this blog.

Find recent content on the main index or look in the archives to find all content.



Author Archives

Powered by Movable Type 4.381

Site Meter