Re: Humans most prim. existing family - a Flatworm?

Lane Lewis wrote:

> Sea creature mistaken for its lunch
> 
> Worm victim of mistaken identity reclassified.
> 21 August 2003
> HELEN R PILCHER
> 
> 
> http://www.nature.com/nsu/030818/030818-11.html
> 
> 
> Imagine being called a bag of chips, just because that was your last supper.
> This unlikely fate befell an obscure marine worm, new research has revealed.
> 
> The amorphous greenish-yellow sea creature was wrongly classified as a
> mollusk because specimens contained mollusk DNA and eggs. "Basically, the
> mollusk material was lunch," explains animal evolutionist Maximilian Telford
> of the University Museum of Zoology in Cambridge, UK.
> 
> Telford's team compared the DNA in fresh finds dredged up from soft mud 100
> meters under a Swedish fjord. They conclude that the creature - called
> Xenoturbella bocki - is a worm.


I think the moral of this story (aside from being sure what part of the 
organism you are sequencing) is that "worm" is a taxonomically useless term.


> It is the most primitive existing member of the group to which humans
> belong, called the deuterostomes, the authors argue. "It tells us what we
> evolved from 500 million years ago," says Telford. Deuterostomes include
> mammals, fish, starfish and worms.


Well, actually, the only known deuterostome "worms" are acorn worms, a 
group of cephalochordates. All the other "worms" are protostomes of one 
sort or another.


> The creature's rocky road to recognition began with its discovery more than
> 80 years ago. It's lack of recognizable features - it has no separate mouth
> or anus and no body cavity - led to its first labeling as a primitive
> flatworm.
> 
> Subsequent studies related it to acorn worms and starfish, because of
> similarities in its diffuse nerve network and outer epidermal layer. Then,
> in 1997, it received the lamentable mollusk moniker.


Still annoyingly vague. Is it specifically related to acorn worms, or is 
it a new "phylum", perhaps the sister group of all the other living 
deuterostomes?

Science journalism. Feh.


> A preference for sludgy sea habitats makes Xenoturbella difficult to find,
> so researchers can only guess at their numbers. "Quite possibly, they're
> everywhere," says Telford, "but they're not the sort of thing you trip over
> on a beach."
> 
> Lane
> 
>