Opabinia regalis is an extinct stem-group arthropod from the Cambrian Explosion, dating to the Middle Cambrian (~505 million years ago). It is distinguished by its unusual morphology, including a barbed proboscis, five stalked compound eyes, and fifteen imbricating biramous lobes running along a segmented body that terminates in a fan-shaped tail.

The species was first discovered in the Burgess Shale by Charles Doolittle Walcott, who described it in 1912 and initially classified it as a putative annelid. A more detailed reassessment by Harry B. Whittington in 1975 demonstrated that Opabinia could not be readily assigned to any known phylum, helping to fuel ongoing debates about the nature of the Cambrian Explosion.

Opabinia is now generally considered part of a stem group of arthropods, only distantly related to forms such as Anomalocaris and possibly to modern tardigrades.

Even though Opabinia is thought to have been a benthic scavenger it was still probably quite agile and capable of evading predators as it foraged about.

It is tempting to regard Opabinia and other long extinct creatures of the period as failed evolutionary "experiments".  However, species tend to be abundant and stable until disrupted by such things as environmental change or predation. Species extinction tends to be brought about by external forces rather than any inherent "design" fault.

It may be the case that Opabinia thrived for many millions of years without leaving any trace. The fossilised remains of such soft bodied creatures are so rare as to make it impossible to draw any clear conclusions. There are indications from other fine lagerstatten deposits around the world that soft bodied creatures did prosper alongside the harder shelled arthropods whose remains are more evident and that some lineages extended far into later periods (Kuhl, et al, 2009).

The collections of hard bodied fossils from around the world represent just a small fraction of the life that was present at any one time. 

 

With thanks to Dr  Jean-Bernard Caron for assistance with anatomical detail.