Europe South Asia Asia Pacific Americas Middle East Africa BBC Homepage World Service Education



Front Page

World

UK

UK Politics

Business

Sci/Tech

Health

Education

Sport

Entertainment

Talking Point

In Depth

On Air

Archive
Feedback
Low Graphics
Help

Thursday, March 18, 1999 Published at 23:16 GMT


Sci/Tech

When we were worms

Acoels: These specimens are about six millimetres long

Take a good look at these curious creatures. Scientists from Spain and the UK believe they can help explain why some animals like humans have a left and a right side.

Researchers agree that the first multicelluar animals on Earth were circular in shape - much like the jellyfish and sea anemones of today - and it was only at a later stage in evolution that body shapes with bilateral symmetry (a right and a left side) began to emerge.

It was a crucially important development in history because features such as legs, fins and wings can only develop on bilateral organisms. But precisely when these creatures came on to the scene is something of a mystery.

The assumption is that most of them arose during a dramatic diversification of animal life - dubbed the Cambrian explosion - some 540-500 million years ago.

The ancestors of nearly all major modern animal groups, or phyla, can be found in the fossil record from this period.

Early emergence

However, evidence has been growing that they might have emerged much earlier. And a new study published in the journal Science would appear to confirm this by identifying a group of modern flatworms called the Acoela as the living descendants of an early lineage from this pre-Cambrian time.

The scientists were attracted to the Acoela because of their uniqueness. Unlike other flatworms they have no digestive tract of any sort.

To find out whether they should be reclassified, the team undertook an analysis of a specific gene common to the Acoela - the "18S rDNA" gene - and many other animals. This gene mutates at a constant rate and can be used to measure the _genetic distance_ between organisms.

In other words, the more variation that exists between organisms, the more distantly they are related - and the greater the time since they diverged from their common ancestor.

Fossil search

According to the results of the study, the Acoela were the first group of bilaterals to split off from the radial (circular) organisms, well before the other flatworms arose in the midst of the Cambrian explosion.

"It may well be that the origin of bilateral organisms occurred a bit earlier on, [before the Cambrian explosion,] from simple animals whose fossils have not been recovered," says Jaume Baguņā of the University of Barcelona.

"This may mean that we need to look more carefully at pre-Cambrian rocks or sediments to search for primitive bilateral animals."

The scientists suggest that the Acoela should now be classified in their own animal group.

Image courtesy of the Coral Reef Research Foundation, Palau.



Advanced options | Search tips




Back to top | BBC News Home | BBC Homepage | Š


Sci/Tech Contents


Relevant Stories

10 Dec 98 | Sci/Tech
Small worm makes history

10 Dec 98 | Sci/Tech
Hunting down the genes

25 Nov 98 | Sci/Tech
Mechanism for evolution described

30 Sep 98 | Sci/Tech
Fossil evidence of worms over one billion years ago





Internet Links


Science magazine

University of Barcelona

UK Natural History Museum


The BBC is not responsible for the content of external internet sites.




In this section

World's smallest transistor

Scientists join forces to study Arctic ozone

Mathematicians crack big puzzle

From Business
The growing threat of internet fraud

Who watches the pilots?

From Health
Cold 'cure' comes one step closer