Vampiroteuthis, a cirrate octopod

To start off, there are two types of octopods, which have little in common other than the fact that they are both coleoid cephalopods, (those without an external shell), are exclusively marine, and have eight arms with suckers. Cirrate octopods have a single row of suckers on each arm and finger-like projecions, cirri, projecting on either side. Incirrate octopods, what most of us probably envision when we think of an octopus, have a double row of suckers on each arm and no cirri. Cirrate octopods have fins and webbing between the arms, incirrate have neither.

Vampiroteuthis infernalis, the only kind of vampiroteuthid so far known, has much in common with cirrate octopods, and little with the incirrate or any of the decapods (squid, cuttlefish, and the like) -- other than what comes from being a cephalopod.  Vampiroteuthis has eight arms, each with a single row of suckers and cirri along either side, webbing between the arms and fins.  Also neither Vampiroteuthis nor cirrate octopods  produces ink which incirrate do.

Vampiroteuthis differs notably from common cirrate octopods in having a pair of narrow sensory filaments that extend from between the first and second pair of arms, unlike the tentacles of decapods that extend from between the third and fifth pairs. The structure and composition of these long filaments is different from that of the arms and in apparently a uniquely derived trait which does not tie it at all with some ten-armed ancestor.

In spite of its name, which means vampire squid, Vampiroteuthis is not a squid, nor does it tie squid and octopods, but is closely related to cirrate octopods to the point it may even be considered as one.

There are good illustrations on various websites, query, including Tree of Life (TOL) and in the FAO Species Catalogue for Fishery Purposes No. 4, Vol. 3, Octopods and Vampire Squids.

Pending, a look a Nautilus. 

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