Wouldn’t that mean that the cephalopods had an even more complex nervous system in the past? For that matter, why do we hear about so much stasis and so little about evolution? The evolution must be happening very fast, punctuated by long periods of stasis.
One reason that Cambrian cephalopods would be very interesting is that the octopus and cuttlefish, apart from being quite complex, are some of the few invertebrates known to be seriously intelligent. Were their ancestors intelligent back then?