Strange worm, Xenoturbella


This odd marine worm, Xenoturbella bocki, is in the news right now, and I had to look it up in Pechenik's Biology of the Invertebrates(amzn/b&n/abe/pwll) to remind myself of what it was. Here's the complete entry:

Xenoturbella bocki

This marine worm, first described in 1949 as an acoel flatworm and later claimed as either an early metazoan offshoot or a primitive deuterostome, has recently been affiliated with primitive bivalve molluscs, based upon a study of gamete development (oogenesis) and an analysis of sequence data from both 18S rRNA and mitochondrial genes. Little is known about its reproductive mode, and developmental studies that might help to resolve the phylogenetic issues are just starting to be reported. A second species was described in 1999.

The animals are up to 4 cm long, vermiform (worm-shaped), and covered by locomotory cilia. They have no digestive tract, and indeed no organs at all. Their only conspicuous morphological feature, other than their cilia, is a statocyst for determining orientation. To date, they have been collected only off the coasts of Sweden and Scotland, in sediments at depths of 20 m to 100 m.

That's it. Part of that is now known to be wrong: the data showing an affinity to the molluscs is an artifact, caused by the fact that it somehow eats bivalves, and partly digested clam material contaminated the samples. Otherwise, not much is known; I've found papers describing the presence of oocytes inside the animal, but no one as far as I know has actually observed its development. It's a strange, mysterious blob of a worm.

Continue reading "Strange worm, Xenoturbella" (on Pharyngula)


No organs? I wonder if it could be a new kind of Parazoa.

This may be a bit off topic, but here’s an article someone ought to do some deeper looking into:[…]02A.xml.html

Japanese researchers find dolphin with ‘remains of legs’

Japanese researchers said Sunday a bottlenose dolphin captured last month has an extra set of fins that could be the remains of back legs, providing further evidence ocean-dwelling mammals once lived on land.

So, has it been offered a job at the California Dept. of Transportation’s planning department yet? It seems to be qualified.

(Sorry, couldn’t resist.)

Any idea how long it will take to evolve? Perhaps isolation of different populations will produce both a primitive worm and a primitive mollusc.

Woah my bad… the mollusc part is wrong. But it’s still an interesting worm isn’t it? Perhaps it has room for improvement.

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