Aegirocassis

Aegirocassis is an extinct genus of radiodont arthropod belonging to the family Hurdiidae that lived 480 million years ago during the early Ordovician. It is known by a single species, Aegirocassis benmoulai. Out of all the Cambrian era arthropods so far named,‭ ‬Aegirocassis has certainly been one of the most remarkable.‭ ‬Obviously the thing that most people notice about Aegirocassis is the huge size,‭ ‬at just over two meters in length for the largest recorded specimen,‭ ‬Aegirocassis was in‭ ‬2015‭ ‬the largest anomalocaridid so far named,‭ ‬as well as amongst the largest arthropods ever discovered. Far more important than the size however,‭ ‬the three dimensional preservation of some of the Aegirocassis specimens has proven that Aegirocassis had two sets of swimming flaps,‭ ‬and not one as had been previously assumed for other anomalocaridids.‭ ‬Before,‭ ‬it had been assumed that anomalocaridids had‭ ‘‬lost‭’ ‬their lower sets in favour of one for easier swimming.‭ ‬Aegirocassis however has proven that the lower set,‭ ‬which originally would have been legs‭ (‬as in lobopods‭)‬,‭ ‬were simply adapted into additional swimming flaps.‭ ‬In addition to this comparisons to specimens of earlier named genera such as Peytoia and Hurdia seems to indicate that these other genera also had two sets of flaps and not just one as had been previously assumed.‭ ‬This two branched limb arrangement is something that is seen in modern arthropod types such as shrimps.