''Myoscolex'' is an early animal species known from the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

Emu Bay Shale The Emu Bay Shale is a geological formation in Emu Bay, South Australia, containing a major Konservat-Lagerstätte (fossil beds with soft tissue preservation). It is one of two in the world containing Redlichiidan trilobites. The Emu Bay Shale ...

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

. It was interpreted as an annelid and some supports that theory, while it was also considered as an arthropod close to ''

Opabinia ''Opabinia regalis'' is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte (505 million years ago) of British Columbia. ''Opabinia'' was a soft-bodied animal, measuring up to 7 cm in body length, and it ...

'', through other studies questions that interpretation. ''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

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. However in 2022, new

opabiniid Opabiniidae is an extinct family of bizarre marine stem- arthropods. Its type and best-known genus is ''Opabinia''. It also contains ''Utaurora''. Opabiniids closely resemble radiodonts, but their frontal appendages were basally fused into a pr ...

Utaurora ''Utaurora'' is an extinct genus of opabiniid, which were bizarre stem-arthropods closely related to true arthropods and radiodonts; the type species is ''U. comosa''. The animal's fossils come from the Cambrian of Utah. This genus is so far ...

'' was described and ''Myoscolex'' is considered as animal with unknown affinity.

As a Polychaete

''Myoscolex'' 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 ''Pikaia gracilens'' is an extinct, primitive chordate animal known from the Middle Cambrian Burgess Shale of British Columbia. Described in 1911 by Charles Doolittle Walcott as an annelid, and in 1979 by Harry B. Whittington and Simon Conway ...

'', and without the use of chaetae for propulsion, unlike other polychaetes.

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, and possibly eyes and proboscis. The inner two layers were the internal muscles mineralized in

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...

with resounding detail.

References

Prehistoric protostome genera Prehistoric invertebrates of Oceania Controversial taxa Emu Bay Shale {{Cambrian-animal-stub