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Could well be John. Octopus certainly leave drill holes in shells, I'm not sure how similar the radula was on a nautiloid to that of octopus though. They probably pretty much ate anything smaller than them and scurrying I'd imagine. Ordovician trilobites needed their defensive spines for some reason, and nautiloids were top predator...
While it could be a nautiloid, The holes don't seem right. Cephalopods drill bivalve shells in order to inject a venom that will kill or atleast nearly kill the animal inside, put them pull the shell and eat from the opened shell. This means that the hole needs to only be a pin prick. drilling as small of whole as you need with a radula will generally produce an oval drill. These holes seem to be more rounded and larger than one would expect from a hole merely intended for venom injection. This appears to be more like a gastropod drill, which feed through the hole rather than pulling the shell. This probably is not gastrood either, however, as drilling gastropods aren't thought to have evolved untill 110 million years ago, formly in the Mesozoic, long after these poor brachiopods met their fate.
Methinks this paper cited below help us this case. Unfortunately it would cost a subscription to obtain it. Is there anyone out there who could gain a free copy via an educational institution who could help please?