25. fill in the correct remaining nucleotides.

Cephalopods are widely regarded as the most intelligent of the invertebrates, and have well developed senses and large brains (larger than those of gastropods).the nervous system of cephalopods is the most complex of the invertebratesand their brain-to-body-mass ratio falls between that of endothermic and ectothermic vertebrates.the brain is protected in a cartilaginous cranium. the giant nerve fibers of the cephalopod mantle have been widely used for many years as experimental material in neurophysiology; their large diameter (due to lack of myelination) makes them relatively easy to study compared with other animals. cephalopods have also been known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on the crabs, and return to their own aquarium. cephalopods are social creatures; when isolated from their own kind, they will sometimes shoal with fish.