According to the Merriam-Webster Dictionary cephalopod means "marine mollusks including the squids, cuttlefishes, and octopuses that move by expelling water from a tubular siphon under the head and that have a group of muscular usually sucker-bearing arms around the front of the head, highly developed eyes"
According to the Etymology Dictionary cephalopod derives from Greek cephalo-(chephale) means "head" and -pod (podos) means "foot"
Cephalotorax has got the same root as cephalopod. Other words with Cephalo- are: electrocefalogram, microcephalic, hidrocephalic
Other words with the root -pod are: arthropod, gastropod ,tripod.