Squid
Description
Cephalopods have the most highly developed nervous systems among invertebrates. Squids have a complex brain in the form of a nerve ring encircling the oesophagus, enclosed in a cartilaginous cranium. Paired cerebral ganglia above the oesophagus receive sensory information from the eyes and statocysts, and further ganglia below control the muscles of the mouth, foot, mantle and viscera. Giant axons up to 1 mm (0.039 in) in diameter convey nerve messages with great rapidity to the circular muscles of the mantle wall, allowing a synchronous, powerful contraction and maximum speed in the jet propulsion system.
Squid-20