They are most related to other cephalopods like squid or cuttlefish.
They are distantly related to other mollusks such as oysters or slugs.
octopus
squids and octopus.
Squids
No. Lobsters are related to spiders and scorpions, but nobody knows if octopus and squid are.
A cat fish An octopus
The squid and the cuttlefish. Wikipedia has more information, and a link is provided.
I think the difference is that cuttlefish has less legs than an octopus. =) =ㅇ =D!An octopus also has no shell, while cuttlefish have an internal shell
They are related: cousins of sorts. see: http://www.thecephalopodpage.org/
I think it depends on the type of octopus. I think the most common type of octopus is called the Common Octopus (octopus vulgaris). Hence the name! One of the most venemous types of octopus is the Blue Ringed octopus. If you are looking for a better answer search for 'types of octopuses' and maybe it will tell you which ones are more common.
Some of it's relatives are cuttle fish, squid and octopus.
There is no such thing as a cuddlefish. It is called a "cuttlefish", and it is a large mollusc that is related to the squid and octopus.
Although related cephalapod species do have shells elements either external or internal, octopi do not.