Class Cephalopoda
General characteristics: They are the most complex invertebrates and mulluscs , The foot of a cephalopoda has evolved into tentacles or arms used for capturing prey, movement , and attachment. The foot in Cephalopods is incorporated into the mantle cavity and the head is in line with the visceral mass. The mantle of a cephalopods encloses all of the body except the arms and head , and it acts as a pump to deliver water to the mantle cavity.
shell: Ancestral cephalopods had a conical shell ,as nautilus are the only cephalopods that have a shell that's external. The nautilus secrete new shells around itself as it grows and they leave the empty septum behind , only the last chamber of the shell is occupied and are filled with fluid when formed. Their is a tissue called siphuncle that perforates the septa. In all other cephalopods the shell is absent or nonexistent. In cuttle fish the shell is internal and in thin layers , that make them buoyant. The shell of a squid is also internal called a pen and it helps keep their balance as it supports the mantle.
Locomotion: Cephalopods move using a jet proportion system from the mantle muscles contracting , and since the mantle encloses the body water is shot out through a narrow funnel. Radial mantles muscles bring water into the mantle by increasing its volume of the cavity. Posterior fins act as stabilizers for cephalopods and jet propulsion is usually used for escaping predators .
Feeding and digestion: Most cephalopods locate prey by sight do to their large eye muscles , and catch them with the suction cups on their arms. All cephalopods have jaws and radula , with beak like structures for tearing through food and then the radula forces it into its mouth. The digestive tract of cephalopods are peristalsis and muscular, and most digestion occurs in the stomach and a large cecum. Digestion is extra-cellular with digestive gland supplying enzymes. The intestines end at the anus and exhalant water carries waste out the mantle cavity.
Maintenance functions: Cephalopods have a closed circulatory system , blood is confined to the vessels, capillary beds connect to arteries and veins , and exchanges of gases , nutrients , and metabolic waste occur across capillary walls. The heart has two auricles and one ventricle, they also have branchial hearts. These modifications are necessary because of the creatures high metabolic rate and they need a increase blood flow rate. The brains of cephalopods are large and forms from fusion of the ganglia, the large areas control muscle contraction, sensory perception , and memory. Cephalopodas eyes are similar to vertebrate eyes , although they have no blind spots because the nerve cells can leave the eye from the outside of the eyeball. The eyes of cephalopods can form images , distinguish shapes , and discriminate certain colors. Pigments cells in their eyes called chromatophores can change color of the animal, this is used as a alarm response combined with ink discharge.
Learning:The complex nervous system of cephalopods are way different then other molluscs , They are very adapative and can be trained. Cephalopods are observational learners . Do to their short life spans and antisocial structure scientist believe these creatures learn through avoiding predators while being predators themselves. Cephalopods also have a variety of food sources to choose from and many escape and diversionary tactics to avoid predators which could hint for increased intelligence.
Reproduction and development: Dioecious with gonads in the viseral mass located in the dorsal portion of cepholopods , males reproductive tract consist of testes and structures for encasing spermatophores. One tentacle of the male cephalopods called hectocotylus is modified for spermatophore transfer. During copulation , male and female tentacles interwine, and the male removes spermatophores from his mantle cavity and places them in the female. Cephalopods develop in the confines of the the egg membrane and are hatched as mini adults .