Myoscolex

Myoscolex; Temporal range: 517 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ Early Cambrian
	Myoscolex ateles
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	†Dinocaridida
Family:	†Opabiniidae (?)
Genus:	†Myoscolex

Myoscolex is an early animal species known from the Cambrian Emu Bay Shale in South Australia. Originally interpreted as an annelid, it seems to be an arthropod; the possible presence of an Opabinia-like proboscis, eyes, and flaps suggests a plausible relationship with that species.[1] Myoscolex is the earliest known example of phosphotized muscle tissue, and as to which shows distinct annulation.

Etymology

Myoscolex ateles derives its name from Greek, "Myo-" meaning muscle, "Scolex" meaning worm, and "Ateles" meaning incomplete. This definition of "Incomplete muscle worm" is due to its initial identification as a "muscular" annelid worm with indistinct features after fossilization.

Description

Restoration of Myoscolex ateles, as an opabinid

As an Opabiniid

When described as an Opabiniid, Myoscolex is said to have at least 3 eyes, a thin proboscis jutting from under the proposed eyes, lateral lobes on the trunk, a tail fan on the posterior segments, and an upwardly curving trunk. It would have lived as a fast nektonic carnivore.

As a Polychaete

Myscolex as a polychaete worm was unconventional in appearance being laterally flattened body with "rods" protruding from the ventral side. Movement would have been an undulation similar to that of Pikaia, and without the use of chaetae for propulsion, unlike other polychaetes.[2]

Preservation

Myoscolex was preserved laterally compressed and in 4 layers. The outer two layers are composed of Calcium carbonate and represents the skin,rods,lateral lobes, eyes, and proboscis. The inner two layers were the internal muscles mineralized in Apatite with resounding detail.[1]

References

Briggs, D. E. G.; Nedin, C. (1997). "The Taphonomy and Affinities of the Problematic Fossil Myoscolex from the Lower Cambrian Emu Bay Shale of South Australia". Journal of Paleontology. 71 (1): 22–32. doi:10.1017/S0022336000038919. JSTOR 1306537.
Dzik, Jerzy (January 2004). "Anatomy and relationships of the Early Cambrian worm Myoscolex". Zoologica Scripta. 33 (1): 57–69. doi:10.1111/j.1463-6409.2004.00136.x. ISSN 0300-3256.

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[Briggs1997-1] Briggs, D. E. G.; Nedin, C. (1997). "The Taphonomy and Affinities of the Problematic Fossil Myoscolex from the Lower Cambrian Emu Bay Shale of South Australia". Journal of Paleontology. 71 (1): 22–32. doi:10.1017/S0022336000038919. JSTOR 1306537.

[2] Dzik, Jerzy (January 2004). "Anatomy and relationships of the Early Cambrian worm Myoscolex". Zoologica Scripta. 33 (1): 57–69. doi:10.1111/j.1463-6409.2004.00136.x. ISSN 0300-3256.