Since octopodes are invertebrates, they have no joints.
How about: To qualify as a limb, in vertebrates, there must be at least one joint.
According to Colibri, in post #24:
Italics mine
That will walk.
(Get it? Limb, walk?)
so, to follow up: it’s because our ancestors were four-finned fish, with two pairs.
are four-fins a better arrangement for swimming/fluid dynamics than six fins might be?
The earliest jawed fish apparently only had one set of paired fins, equivalent to the pectoral fins. I’m not sure when pelvic fins appeared.
I don’t see any reason why a six-finned fish couldn’t have evolved. Some crustaceans have many pairs of swimming legs.
In insects, the wings are homologous to the legs, but then, so are the antennae, some of the mouthparts, and several other structures. The first arthropods looked rather like centipedes, with some number of repeated nearly-identical body segments, each of which had two appendages. Along the line that led to the insects, those segments (and the appendages attached to them) specialized for various purposes, and many segments each fused into three main body divisions. But it’s fairly easy to revert those specializations, and so (for instance) to end up with a fruit fly with legs sprouting out of its head.
In the aquarium fish I am familiar with, the other paired fins, the ventral, don’t seem terribly useful.
Most fish mainly use the tail fin for propulsion, and the paired fins mostly only for steering and control. There are exceptions.
Yep.
The ventrals on a beta appear to be merely decorative.
On a killifish, they are insignificant save for appearance.
And he is damned pretty.
Vertebrate anatomy would have to be strikingly different to facilitate additional pairs of limbs. The skeleton would add more weight for little gain, and the limbs themselves would add weight and consume energy for minimal or no payback. Insect legs contribute a lot less to their body mass, and the circulatory system that supports them is somewhat less complex than that of most vertebrates.
So, really, one reason for the four limb arrangement of vertebrates is that it is practical. I mean, look at centaurs: darn ungainly critters. What the hell do you do with that extra stomach, anyway?
Oh yeah?
What about Tars Tarkas?
I still think the DC comics in the mid-70s had the best imagining for Tars Tarkas.
Did you miss the bit where they have to use their cerci to do it?
Then Groucho would have had to say:
“One morning I shot an elekey/monkphant (?) in my pajamas. How he got his 6 limbs in my pajamas I’ll never know.”
You mean like this? Naah.
Here’s the one I like best. Prob 'cuz it was on the cover of the first Barsoom book I read
I don’t recall how Burroughs described him, but I recall drawings where they were more heavily muscled.
Might as well include Zaphod in the mix, then. Unless you prefer not to have your head smacked with a slice of lemon wrapped around a large gold brick.
I suppose one might wonder what would happen if you crossed Zaphod Beeblebrox with a monkaphant, but knowing his proclivities, it’s probably already happened.
This is becoming boring, but (Zaphod Beeblebrox)*(monkaphant)*sine(theta).