The bigfin squid (Magnapinna s.) is a cryptid, meaning it is an animal for which we have a dearth of information. Specifically, we have only *officially* seen its larval, paralarval, and juvenile stages. No one can confirm that they've seen the adult stage. But we *think* we have.
Photo source: ToLweb.org

Magnapinna is Latin for 'great fin'. This squid earned it because the fins on its head are very large, with distinctive morphology. So when researchers encountered this squid seen above (and in the video below), they saw the fins and thought, hey, we just might have found an adult Magnapinna.
They hadn't expected the long arms (elastic, and reaching a length of 15-20 times the mantle length). That's why the young ones have the name bigfin, and the adults the name long-arm. But the 'adults' have only ever been captured on film, and so have never been studied beneath the scalpel and microscope. Not until then can we confirm any link between the two cryptids.
Watch out for this video; it's flickery, has the feel of the beginnings of a horror film, and the squid reminds me at first glance of the queen alien from Alien.
Thanks for the squid, Christopher. And Happy Halloween.