Spriggina: Annelid worm or proto trilobite arthropod?

[MeargleSchmeargl]

I have wanted to post this debatable topic here since I read up on Spriggina. I want to see your thoughts on the issue. Personally I'm in proto trilobite camp, but I am by no means an expert on this. Can't wait to hear your opinions!

[piranha]

Most agree with Seilacher's Vendobiont interpretation: a variant of Charniodiscus.

 

 

 

 

 

 

 

 

 

[piranha]

Spriggina and allied vendobiont forms:

 

 

Seilacher, A., & Gishlick, A.D. (2015)

Morphodynamics. CRC Press, 514 pp.

 

 

Selden & Nudds: not a 'worm'

 

Spriggina is a small organism with a horseshoe-shaped ‘head’ followed by an elongate, leaf-like body composed of two rows of short segments either side of a medial line. At first, Spriggina was thought to resemble a polychaete worm such as Nereis, but a close look at the segmentation reveals that the segments do not match across the mid-line, just as in Dickinsonia. Seilacher (1989) turned the interpretation upside-down, suggesting that Spriggina could be another type of sea-pen, and that the ‘head’ was actually a holdfast.

 

Selden, P.A., & Nudds, J.A. (2012)

Evolution of Fossil Ecosystems

Academic Press, 288 pp.

 

 

Seilacher: not a 'trilobite'

 

In Spriggina and related shorter forms (Parvancorina, Vendomia, Vendia, Fig. 2), in contrast, the polar difference between the two ends is very pronounced - in fact so much so that one is tempted to call them the ‘missing link’ between annelid worms and trilobite arthropods. However, there is the problem of functional transformation. The broad pleural lobes of trilobites served primarily as a rigid hood under which the legs could process the sediment for food (Seilacher 1985b). So why make such structures while there were still no legs and no rigid exoskeleton?

 

Seilacher, A. (1989)

Vendozoa: organismic construction in the Proterozoic biosphere.

Lethaia, 22(3):229-239

[erose]

You needed a third "other" choice. The symmetry doesn't appear to be there for either.

[Fruitbat]

I'm in the camp for 'Other'. Birket-Smith (1981) concluded that Spriggina could not be classified as an annelid or an arthropod according to our present-day definitions and should be placed in a phylum of its own. He also suggested that trilobites evolved from Spriggina or from one of several related forms.

-Joe

[Wrangellian]

I guess you need to redo the poll...