Apparently yesterday was International Cephalopod Awareness Day. This is one of the problems of living on the other side of the world from the blogging majority - by the time I discovered that October 8 was Cephalopod Day, October 8 was, for me, pretty much over. Mind you, except for Ben D at Principles of Parsimony, Cephalopod Awareness seemed to mostly be Neocoleoid Awareness. Unfortunately, modern cephalopods are something of a fragment of their former selves. Of the three traditional subclasses, only one - the coleoids - survives in any great numbers. 'Nautiloids'* are represented by only a single living genus, the eponymous Nautilus. The third class, the ammonoids (of which ammonites are the best-known members), never made it past the end of the Cretaceous.
*The inverted commas are because Nautiloidea in the traditional sense is a paraphyletic group that contains the ancestors of the other subclasses.
But once these creatures ruled the sea. The image above (from here) is of the largest known ammonite, Parapuzosia seppenradensis, with a diameter of about 2.5 metres. That's a lot of calamari.
Oh yes, and while looking stuff up for this, I came across one of the more disturbing article titles I've seen - "Implosion of living Nautilus under increased pressure". Ick. Can you imagine the grant proposal?