General Characteristics
Shell
- Only living cephalopod with an external shell is the nautilus.
- Septa subdivide its coiled shell
- siphuncle (a cord of tissue) perforate the septa
- All other cephalopods the shell is reduced or absent
- cuttlefish's shell is internal (called cuttle bore)
- the squid's shell is reduced to an internal chitinous structure called the pen
- the octopus's shell is absent
Locomotion
- Jet propulsion system
- mantle contains radial and circular muscles
- circular muscles contract to decrease the volume of the mantle cavity and close the collar like valves to prevent water from moving out of the mantle cavity between the head and the mantle wall
- water is forced out of a narrow funnel
- muscles are attached to the funnel to control the direction of the animals movement
- radial mantle muscles bring water into the mantle cavity by increasing the mantle's volume
- posterior fins act as stabilizers in the squid and aid in propulsion and steering in cuttlefish
- octopuses are more sedentary animals
- jet propulsion is an escape response
- normally they crawl over the substrate using tentacles
Feeding and Digestion
|
|
Other Maintenance
- cephalopods, unlike other molluscs, have a closed circulatory system and blood is confined to vessels throughout its circut around the body
- capilary beds connect arteries and veins and exchanges of gases, nutrients, and metabolic washes occur across capillary walls
- branchial hearts contract like arteries and structures
- at the base of each gill and help move blood through the gill
- increase blood pressure
Nervous System
- cephalopod's brains are large and their evolution is directly related to their predatory habits and dexterity
- brain forms by a fusion of ganglia
- large areas are devoted to controlling muscle contractions and sensory perception
- functions such as a memory and decision making
- eyes are similar to vertebrates; has no blind spot though because the nerve cells leave the eye from outside the eyeball
- statocysts respond to gravity and acceleration and are embedded in cartilages next to the brain
- osphtadiacre are only present in nautilis
- chromatephores are pigmented cells that change the color of the animal when muscles attached to them contract