Cephalopoda

The cephalopods ( Cephalopoda , of the Greek képhalé , the head, and pous, podos , the foot) are animal class of the Mollusque S, of which the foot, divided into arm, surmounts the head. The known types of cephalopods are the Pieuvre, the Calmar, the Seiche.

The cephalopods are the Mollusque S most advanced, whose organization reaches the complexity of that of the Vertébré S. Their head, distinct from the visceral mass, comprises a true brain contained in a cartilagineux cranium; improved eyes, a horn nozzle, etc Their foot, which sticks to the head, is divided into arm provided with suction cups. The coat ventral, contractile, constitutes with the siphon a powerful body of locomotion.

The cephalopods exist since the end of the Cambrien, 500 million years ago. The current cephalopods are sailors and carnivorous. They were nourissent of molluscs, fish, and shellfish. They hold their prey with their arms, and shreds it with their horn nozzle. When they are sedentary, one can easily locate their presence by the cluster of shells emptied in front of their hole.

Anatomy

Head

The body is composed of a famous person, carrying two side eyes as complex as those of the Poisson S or the men.

In top opens a mouth, equipped with a nozzle for two mandibles, similar to those of a nozzle of Perroquet, and a Radula with salivary glands.

A solid cartilagineux cranium contains a very complicated brain, and gives fastener to the muscles of the arms and the back.

Their internal ear points out that of the vertebrate ones.

The Nervous system is extremely condensed. Fusion of the cerebroid, palléaux and pedal ganglia results true a Cerveau, from which leave the majority the nerves. It reveals a thorough cephalization and the capacities of solution to problem observed at the Poulpe S, for example, are astonishing.

Arm

These arms around the mouth are tentacles. As regards under class the coléoïdes, one can count of them eight at the Octopode S or ten at the décapode S.

These appendices are sometimes carrying suction cups (it is not the case of Nautiles), which recovers them more or less completely, and are laid out in lines. The suction cups are furnished with teeth or horn hooks. Each suction cup is a sophisticated instrument which applies to its target. A horn ring ensures the sealing, and a body functioning like a piston makes the vacuum inside, ensuring adhesion.

These bodies are used with the capture of the preys, the coupling, and the snaking on the ground.

Body

The body is sometimes in the shape of spindle (Calmar) sometimes in the shape of purse (Pieuvre). It contains a strong cavity containing of the complicated gills, and in which the bodies reproductive, urinary, and the anus open. The mass of the internal organs is leant there.

The skin, which recovers the whole body, forms a fold which limits the cavity branchiale (the nautiloïdes are tétrabranchiaux, 4 gills, and the coléoïdes are dibranchiaux, 2 gills): it is the coat. All this skin is covered with coloured bodies (Chromatophore S), under the action of the brain, which make it possible the cephalopods to abruptly change color. With the top of the pigmented cells exist made iridescent cells, which reflect the light.

These animals are very strong, and of large swimmers. The musculature of the body and the tentacles is very powerful. At the coléoïdes, the octopodes do not have fins and crawl, contrary to the decapodes which have one of them (triangular in position former for the squid and all around the body for the cuttlefish). The presence, the regression or the absence of shell are a reason for which they swim better than the remainder of molluscs. The nautiloïdes have a shell which handicap them in their displacements. On the other hand, at the coléoïdes, the décapodes have an internal shell in position dorsal, but the octopodes them are without shell.

Their heart is very sophisticated. Circulation is itself rather sophisticated. There are arteries, veins, capillaries. The system is not completely closed, but part of blood only passes by gaps, before returning in the middle. Blood is tinted of blue by Hémocyanine, substance containing copper which plays a part similar to hemoglobin for the transport of oxygen.

They have a large liver, a pancreas, a complicated intestine, very developed kidneys.

At the décapodes, one finds under the skin of the back a hard body, which is the shell Mollusque S transformed into a calcareous bone (Seiche) or into a horn body in the shape of feather (Calmar). At the Nautile S, the shell remained external; it is partitioned, traversed by a siphon, and surrounds the body.

Siphon

Between the head and the body is a tubular body, the siphon , which makes it possible to evacuate the water of the cavity palléale and to swim with reculon, by propulsion with reaction.

The coat has rhythmic and very energetic contractions. Each time it dilates, water enters by the opening of the pocket. With each contraction, it is driven out abruptly by the funnel. It results a displacement from it from the animal in contrary direction of the water current.

Under the siphon a gland opens which secret black, some drops are enough to disturb water around the cephalopod, and to enable him to escape, by combining this action with the transformation of its coloring by the play of the chromatophores. The ink of cuttlefish is the Indian ink or Sépia of the draftsmen.

Reproduction

The sexes are separate. The reproduction in the cephalopods is also very sophisticated.

In the male, one or two arms is modified and allows the coupling (Hectocotyle). The Spermatozoïde S are gathered in bags, or Spermatophore S, that the male seizes with one of its arms and introduced into the cavity palléale of the female. Sometimes, the arm copulator is detached in the operation, which made it take by the former naturalists for a parasitic worm.

The eggs are large, and rich in Vitellus ( eggs télolécithes ). Generally they are laid joined together in glaireuses layings or black bunches (cuttlefish), which one calls the " grapes of mer". In the argonaute, the secret female a calcareous nacelle to contain them.

The segmentation of egg is partial. The development is direct.

Classification

In the class of the cephalopods one meets Mollusque S advanced sailors which could form part, at varied geological times, the principal predatory ones of the oceans.

There are nothing any more but two lignées :

  • the group of the Nautiloïdes with some species (appeared in Cambrien)
  • the group of the Coléoïdes which includes/understands the Calmar S, the cuttlefish S, the Pieuvre S and the vampires of the seas with more than 700 species. (appeared with the Dévonien)

The group of the Ammonoïdes , appeared in Dévonien, died out with the higher Crétacé.

Place des cephalopods in the animal kingdom

Clean characters of the group

The anatomical organization of the cephalopods is marked by the présence :
  • of a drifting funnel of the foot of molluscs being used with the locomotion and the irrigation,
  • of arm carrying of the suction cups surrounding the mouth and forming a crown of Tentacle S,
  • of a pair of jaws corneas which sometimes fossilize (they are the aptychus ) or of a Opercule.
  • of advanced and powerful eyes.
  • according to the groups, of a shell with room and Siphon, of a shell intern sometimes reduced to a chitinous feather or of any framework (as for octopuses).
Their shell, when they have one of them, is made up of partitioned a part known as phragmocône.

According to ITIS

According to other sources

  • Subclass: Nautiloidea
*Fam: Nautilidae (family of the nautile) *Super-ordre: Octopodiformes (cephalopods with eight arm) - Octobrachia Fioroni, 1981
*Ordre: Vampyromorphida
*Fam: Vampyroteuthidae (family of the squid vampire)
*Ordre: Octopoda (octopuses or octopuses)
*Sous-ordre: Cirrata
*Sous-ordre: Incirrata
*Tribu: Argonautida
*Fam: Alloposidae
*Fam: Argonautidae
*Fam: Ocythoidae
*Fam: Tremoctopodidae
*Tribu: ----
*Fam: Amphitretidae
*Fam: Bolitaenidae
*Fam: Octopodidae (family of the Octopus).
*Fam: Vitreledonellidae
*Fam: Bolitaenidae
*Super-ordre: Decapodiformes (cephalopods with 10 arms: squids and cuttlefish) - Decabrachia Boettger, 1952
*Ordre: Oegopsida
*nombreuses families
*Ordre: Myopsida
*Fam: Loliginidae
*Fam: Chtenopterygidae
*Fam: Bathyteuthidae
*Ordre: Sepioidea
*Fam: Sepiidae
*Fam: Spirulidae
*Fam: Idiosepiidae
*Fam: Sepiadariidae
*Fam: Sepiolidae

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