The head is rudimentary and lacks eyes and tentacles. It feeds by contractile filaments called captacula, which are withdrawn into the body cavity when they meet up with food. All scaphopoda are marine, and live buried in muddy or sandy bottoms, where they feed on detritus . This class includes octopus, squid, cuttlefish and nautilus. They are bilaterally symmetrical and often highly streamlined.
Tentacles surround the head, and a funnel coming from the mantle produces jet propulsion.
Only a few cephalopoda produce a calcareous shell. All are marine inhabitants and are predators or scavengers. They range in size from 10 millimeters to 20 meters for the giant squid. They have a head with cephalic tentacles and a well-developed foot used in crawling. Some gastropods have lungs for respiration, others gills.