Spriggina floundersi  is an extinct segmented organism from the Ediacaran period (635 ma - 543 ma) which grew to around 40 - 50 mm and it is one of the earliest complex multi-cellular organisms to appear on Earth. It was discovered by Reg Sprigg in 1940's within the Ediacaran Hills of the Flinders Ranges of South Australia - from which the Ediacaran period received its name. It has become one of the most keenly studied Ediacaran organisms but its affinities are still unknown.

Spriggina floundersi model from Paleozoo Evolutionary Models by Bruce Currie

Spriggina is of great interest to palaeontology because it combines a number of key evolutionary traits. These include: bilateral symmetry (disputed), a "head" and a "tail", motility, the suggestion of a mouth and digestive tract and possible light sensitive buds on its horseshoe shaped head which has similarities to the trilobite cephalon.

Spriggina was first classified as an annelid (Glaessner, 1957), because of its worm like segmentation but later analysis suggests that Spriggina may be more closely related to the arthropoda phylum and possibly the trilobita class (McMenamin, 2003). This has been countered by other analysis that points to Spriggina having a glide-reflection morphology rather than bilateral symmetry - precluding it from the arthropod phylum - although this discrepancy has been attributed to taphonomic processes or distortions incurred during fossilisation. The fossils of this period tend to lie within relatively coarse matrixes so impressions lack precise detail, making it hard to draw conclusive observations. 

The relatively advanced morphology and motility (the ability to move independently) of Spriggina has led to speculation that it was one of the first predators on Earth.

The evolution of motility  is thought to have initially facilitated scavenging - with organisms feeding on microbial mats and detritus (Gehling, Droser, 2018) - but progressively it underpinned the development of overt predatory behaviour. Predation is subsequently thought to have played a key role in the collapse of Ediacaran ecosystems and to have stimulated the biological arms race that was to follow in the Cambrian period. 

Spriggina floundersi  became the state fossil emblem of South Australia in 2017.

With thanks to Prof.Jim Gehling for feedback on anatomical detail.