Then what is an octopus?
a
mollusc.
An insect?
no, insects are
arthropods.
Sorry, but an octopus is a sea animal because it's a form of fish.
you can't be serious. you're putting us on, right? this is a joke? do i need to show you pictures of fish and octopodes? they're clearly not the same thing. for one, an octopus isn't even a vertebrate. actually, it's not even a CHORDATE. it has no spinal column. it has a nervous system, but it's not centralized in the same way a fish's (or a human's) is.
you'll note that tetrapods (four-legged animals) are all related to fish, but that octopodes (8 legs) and teuthoids (10 legs) are not tetrapods. neither are arthropods (number of legs varies). all are animals.
the octopus is more closely related to
snails. really. here's 2/3rds of an exam question from my 2nd
intro paleo course, that i just happen to have on hand. (i've labelled it for clarity)
click to expand
octopodes and teuthoids are basically the same as early nautiloids, minus the shell. early nautiloid are basically snails with snorkels an appendages. that diagram's
from memory. you could easily dig up much more information (like, actual fossils) if you do some real research. and for that matter, i draw a lot better when not under pressure and time constraints.
Edited by arachnophilia, : No reason given.