I’m looking for a creature (animal, bug, fish, whatever) that has an endoskeleton and an exoskeleton. Is there such a thing?
This is my first thread, Dopers please be kind!
I suspect there aren’t any, but the chelonian reptiles (turtles, tortoises, terrapins) might come closest. Their shells aren’t true exoskeletons but they are supported on a bony framework that is connected back to their internal skeletons.
Creatures with exoskeletons wouldn’t have much need for a full internal skeleton as well, and it would be a nightmare designing the joints for it that would work in concert with the joints of the exoskeleton.
They also tend to grow through a process called ecdysis, in which the shell moults off periodically and the animal puts on a spurt of growth before the new one has had a chance to harden. An internal skeleton wouldn’t be much use to an animal that lived that way.
Armadillos apparently are, even though they don’t use it for movement. I suppose tortoses are too, since their shell is attached to their bodies by muscles that allow them to withdraw into their shells.
It’s going to depend on what you mean be an exoskeleton and an endoskeleton. The terms are arther vgue. If you just mean a critter with both internal and external rigid suporting structures a few examples come to mind: seahorses, starfish/sea urchins, barnacles in an odd way.
As a matter of curiousity, is there any particular reason why, or did you just wonder?
Were there some dinosaurs with enough scales to count?
<dang> Should think before posting. :smack:
One of the basic uses of an exoskeleton is to give the muscles anchor points for movement, which mean that an armadillo doesn’t have an exoskeleton since it only uses the armor for defense and the internal skeleton for movement.
:smack:
Nope. There were a number of armored types, but those tended to be boney scutes, not anything that could be even remotely considered an exoskeleton.
I suppose one could argue that since most vertebrate heads are sort of exoskeletal since the hard outside surrounds most of the squishy insides.
Maybe this guy fits the bill ? 
Using that definition, turtles indeed would qualify, since their shoulder and hip girdles have become fused to the shell. In this case, what was originally an endoskelton has become partly an exoskeleton.
Another candidate is the boxfish, which along with related trunkfishes and cowfishes, has an external rigid “skeleton.”
It should also be pointed out that the exoskeletons of insects and other arthopods are in fact partly internal. They typically have internal projections, especially in the head and the thorax, to which muscles attach. Not all the muscles are attached to the external parts of the skeleton.
There’s also the odd case of the cuttlefish (actually a mollusk) where an exoskeleton has become completely internalized. A mollusk’s shell counts as an exoskeleton, right?
This is actually true in an evolutionary sense. Vertebrates have two kinds of bone: endoskeletal bone, which in embryos develops from a cartilaginous precursor skeleton; and dermal bone, which develops within the skin without going through a cartilaginous stage.
It is thought that dermal bone is an evolutionary descendant of the external armor of some of the earliest jawless fishes, which was essentially an exoskeleton. Endoskeletal bone corresponds to their original endoskeleton.
The outer bones of the braincase are dermal bones, while the internal bones are endoskeletal (as is the spine, ribs, and limbs). Therefore the bones of the cranium are in large part a remnant of the exoskeleton of our ancient ancestors.
scared the crap outta me…grrr…