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“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.” – Neil Armstrong (1930-2012)

Fresh Reads from the Science 'o sphere!

Tuesday, July 10, 2007

A Squirmy Jellyfish

Scientists from Oxford University have discovered that a very rare, gutless, worm-like animal called Buddenbrockia is more closely related to jellyfish than to worms.

First described in 1851, Buddenbrockia is a bizarre animal because it is missing many features that true worms should have.

Lead scientist Prof. Peter Holland explained that:

"It has no mouth, no gut, no brain and no nerve cord. It doesn’t have a left or right side or a top or bottom – we can’t even tell which end is the front!"

Unlike true worms such as planarians, which I've blogged about before, Buddenbrockia doesn't have different specialized organs on different sides of its body.

Prof. Holland added that:

"Buddenbrockia is very unusual in not displaying this kind of body asymmetry. Seen in cross section it is completely symmetrical so no way is ‘up’ and no direction is ‘forward’."

So it IS made up of the same mushy meat throughout its body.

Based on DNA analysis, Prof. Holland's team discovered that Buddenbrockia is more closely related to jellyfish and sea anemone.

Which means that it is classified under the Phylum Cnidaria, a group of animals that are diploblastic - they have two embryonic germ layers: endoderm and ectoderm.

Other animals, such as true worms and vertebrates like us, are classified in a group called Bilateria. Such animals are triploblastic, containing three embryonic germ layers: endoderm, mesoderm and ectoderm.

So this is a particularly striking example of convergent evolution, where animals from different phyla can end up with the same body shape.

While Buddenbrockia is a diploblastic animal like the jellyfish, it doesn't appear to have an opening of any sort.

Perhaps it is tiny enough to absorb nutrients from the environment through its surface.

Jellyfish are not so lucky.

As Cervantes (from Stayin' Alive) describes in excruciating detail:

"You may have noticed that one thing that all of the triploblastic organisms have in common is a gut, a hollow tube running through the body. The food goes in one end, gets serially disassembled and the useful components absorbed, and the waste goes out the other end.

That is a major innovation, and for those contemplating possible options for reincarnation, it's a good reason to request not to come back as a diploblastic jellyfish. (Thanks to Jan Pechenik for this observation.) The food comes in, and the waste goes out, through the same opening. Life without an anus is clearly inferior. Not only is it impossible to take a meal until the last one has been discharged, but movement involves physical distortion of the digestive cavity and expulsion of much of what is in there. So, you can't digest and swim at the same time. Finally, you have to discharge your gametes and embryos through the same opening. Yuck.

So, let's hear it for one of our most important body parts, that gets very little respect."

Dammit I was eating.

Would you like to know more?

About other bizarre organisms
Magnetic bacteria
Planarian worm