Palaeontology has published a detailed study of the teeth of priapulids in the Burgess Shale.
"As teeth are the most hardy and resilient parts of animals, they are
much more common as fossils than whole soft-bodied specimens," he explained.
"But when these teeth - which are only about a millimetre long - are
found, they are easily misidentified as algal spores, rather than as
parts of animals. Now that we understand the structure of these tiny
fossils, we are much better placed to a wide suite of enigmatic
fossils."
Not familiar with penis worms? An article in
Nature explains that understanding the anatomy of the priapulids is central to a proper understanding of evolution:
...a major step in evolution occurred when an embryonic ball of cells
formed two indentations as opposed to one, giving way to a separate
mouth and an anus rather than the single opening that creatures such as
jellyfish and sea anemones have. In 1908, animals with a mouth and anus
were divided into two groups. In the protostomes (from the Greek for
‘mouth first’), the mouth formed first, and the anus second. In the
other, the deuterostomes (‘mouth second’), the mouth formed after the
anus...
Today, the protostomes include priapulids and most other invertebrates.
The deuterostomes include vertebrates such as humans and a few spineless
animal lineages... Now, using molecular techniques to analyse gene expression, Hejnol and
his team have revealed that a primitive protostome, the priapulid Priapus caudatus, develops like a deuterostome...
More details at the link, and at the
Washington Post, where there is a video of a penis worm. You learn something every day.
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