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Mazon Creek: Sea Cucumbers?


araucaria1959

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Hello,

here are two purported sea cucumbers among some Mazon Creek material I purchased some time ago. The first, better preserved specimen (with counterpart) was labeled without genus, the second specimen was labeled as Achistrum sp. when I got them.

Is this correct? The second one looks like some Achistrum material depicted in the net, though my specimen is small (about 2 cm) and possibly only a fragment. However, I don't see anything specific in this specimen that reminds me of a sea cucumber, but the specimens "in the net" (google picture search) are of similar "structure" (except that they are longer/more complete).

The first specimen (28 mm long) is different from that material, e.g. with "undulated" distal part of the body; I can well image that this can be a sea cucumber (much more plausible than my specimen of purported "Achistrum").

However, since it's so different compared to the material of Achistrum that is usually depicted, this rises the question whether specimen 1 is another genus or if it is only another (better?) style of preservation of Achistrum? Or no sea cucumber at all?

Thanks,

araucaria1959

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The first specimen appears to me to be an Echiuran or Spoon Worm. These worms are often times referred to as leeches to collectors although they are no related.

The species is Coprinoscolex ellogimus and it is probably the most commonly found worm at Pit 11. C. ellogimus is the earliest known echiuran in the fossil record.

The second specimen is a bit more difficult. It Is most likely another Coprinoscolex however it may be an Achistrum sp. Either way it is a partial. If you have a microscope look at the fossil and see if you can detect any fishhook shaped structures. These are called Sigmoid Hooks and are found on the body of sea cucumbers.

Hope that helps!

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Thank you very much for this answer - so my doubts concerning the labeling of both specimens were justified.

I googled for the "sigmoidal hooks" I wanted to look for in my second specimen (to find out what magnification I need), and found this link back to the fossilforum:

http://i740.photobucket.com/albums/xx49/pleecan/Mazon%20Creek/IMG00709.jpg

There are no such hooks in my second specimen - so the purported ID for the second specimen is wrong too. Possibly a badly preserved coprolite.

araucaria1959

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