Cephalopod , any member of the class Cephalopoda of the phylum Mollusca , a small group of highly advanced and organized, exclusively marine animals. The octopus , squid , cuttlefish , and chambered nautilus are familiar representatives. The extinct forms outnumber the living, the class having attained great diversity in late Paleozoic and Mesozoic times. The extinct cephalopods are the ammonites, belemnites, and nautiloids, except for five living species of Nautilus. The cephalopods agree with the rest of the Mollusca in basic structure, and the ancestors appear to have the closest affinity with the ancestors of the class Gastropoda.
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Characteristics Description Vocabulary. Class Polychaeta Class scaphopoda. 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.
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. 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.
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.
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Mollusca: Class Cephalopoda
There are approximately to extant species of cephalopods in two subclasses and five orders. Cephalopods are strictly marine and are found in all of the world's oceans. Cephalopoda is the most morphologically and behaviorally complex class in phylum Mollusca. Cephalopoda means "head foot" and this group has the most complex brain of any invertebrate. The arms, tentacles, and funnel are all derivatives of the foot. Members of the order Nautiloidea have more than 90 tentacles; members of orders Sepioidea and Teuthoidea have eight arms and two tentacles; and members of orders Ocotopoidea and Vampyromorpha have eight arms. The mantle surrounds the visceral sac and possesses strong muscles required for contraction of the cavity and respiration.