[Gondring]

Now, for octopi ~ they are NEW as far as animal classes go.

Huh?! Cephalopods go back all the way to the Cambrian. And if you actually meant "order" instead of "class," then you can go back to the Late Cretaceous, with Palaeoctopus newboldi.

[muawiyah]

http://pandasthumb.org/archives/2008/12/the-radiation-o.html should clarify the ones I meant ~ the Antarctic cephalapods and the deep water cephalapods are REALLY DIFFERENT from all the others and were able to colonize the deep seas.

Notice the discussion of some species dispensing with red blood cells entirely.

I think these critters are sufficiently different from their more primitive ancestors who live in warm surface waters to merit special attention.