La Recherche (No 314, November 1998)
Carnivores, the cones are shells as beautiful as they are dangerous
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POISON APPARATUS OF CONUS TEXTILE
Their shells exhibit splendid patterns, but their poisonous harpoons kill fish, other molluscs and even humans. The poison of these predators could however give rise to new analgesics.
If it had there a poetry of the wonders and emotions of intellect, there would not be for it of subject délicieusement exciting to choose than the painting of a spirit requested by some one of these remarkable natural formations which are observed that and there among so many things of figure indifferent and accidental which surrounds us.
Like a pure sound, or a melody system of pure sounds, in the medium of the noises, thus a crystal, a flower, a shell are detached from the ordinary disorder of the whole of the sensitive things. They are to us privileged objects, more understandable with the sight, though more mysterious with the reflexion, that all the others which we see indistinctly. They propose to us étrangement, plain, the ideas of command and imagination, invention and need, law and exception " How not to follow the matter which opens the admirable text of Valéry, the Man and the shell (1), especially if one notes the extreme fascination which can cause the shapes and drawings of the shells of some gastéropodes marine? Among the latter let us distinguish those which one indicates like Conidae . The cones are, indeed, with the porcelains ( Cypraea ), the object of passion maniac of certain collectors. This fascination rests on the extreme diversity of their drawing and their form. Initially for the beauty of their appearance, then for their carnivorous frenzy. " There are some 700 species of the Conus kind, specify George Richard(2), specialist in the cones great depth of News-Calédonie, among most dangerous textile Conus and Conus geographus ". Because they are terribly armed beings and strongly empoisonneurs.
One can refer to the sumptuous handbook of D. Röckel, W Korn and A.J. Kohn to be approached by the diversity concerning the drawing of their coquille(3). Thus the textile cone, that it comes from the Solomon Islands, of New Guinea-News-Guinea, or Madagascar, exhibe a variation of owners in spots, scratches, lattice, networks, sometimes of brown dark on green bottom bronzes. Almost always it shows a varied repetition of triangular reasons, organized in tapes, in subtle rollings up. Some of these triangles are only suggested like wedge-shaped signs, others on the contrary, very supported as those which exhibe textile C verriculum which is in Mauritius. The cone geographer, has to him a shell brown-red, irregularly mottled white points.
This variety of owners, following the example spots of the leopard or stripes of certain fish like the scalar of Brazil, is at the point of meeting of a beam of search which aims at elucidating difficult problems of morphogenèse. Concerning the texture of the drawing of the cones, Hans Meinhardt of the Max-Planck Institute in Tübingen, succeeded in reproducing, in a convincing way, the chemical reactions responsible for the pigmentation of the shells. Its work, which develops the algorithms of generates lies of the various owners and drawings is, this time still, as much of art than of science(4)(I).
In a general way, there exists more than 100 000 mollusc species in the seas. It is one of the most diversified marine junctions which knows the zoology. Among them, the gastéropodes (of the Greek gastêr : belly and pode : foot) are most numerous. They show, in general, a conical, spiral or helicoid shell, of a great regularity.
Those which stop us are the néo-gastéropodes, in which one arranges the cones. They form, morphologiquement, a very homogeneous group appeared tardily, with the Cretaceous (which is closed 65 million years ago). The fact that they are the only ones of all the gastéropodes to exploit certain ecological niches can explain their great current diversity. They colonize various biotopes of the littoral zone and abound more particularly on the platiers and the external slopes of the reefs. They often live in sands.
Confined in the tropical zone, with some exceptions, very abundant in indo-peaceful water, one can say cone, independently of his esthetics, that it is a frightening killer of the underwater worlds. Because all the cones, without exception, are carnivorous. All developed a lethal means to conclude their hunting, a weapon of an astonishing sophistication. In a general way, all these néogastéropodes has a musculeux foot, the plate, which enables them to move. Of their head, well individua- lized, one can initially observe two fine mobile tentacles which carry each one an eye on their external side; then a lengthened siphon which has a respiratory role; then a tentacle which is used as tactile body; below, is a retractile sheath charnue, the proboscis , a horn thus, which can dilate very promptly. At the end of this one is hung a hollow tooth provided with hooks. One names this last " tooth radulaire ", because it represents an extraordinary specialization of the teeth of gastéropodes, the " radula " being, usually, a raspy language provided with lines of teeth. It is the whole of this apparatus which forms the powerful tool of hunting that have the cones.
But Conus textile and Conus geographus do not have the same predatory technique. Conus geographus is piscivorous, and it is a remote hunter, with the manner of an archer. The aguets, dissimulated in sand, it waits until a fish approaches, and there, car on its prey. Once that the tooth radulaire, in the shape of barbed harpoon, and coated with a powerful venom, is expelled, the proboscis is violently dilated. This extensible horn can even reach to exceed the size of the cone. A geographer of 80 mm can gober thus a fish to 130 mm.
The manner of Conus textile is very different. This cone is molluscivore, it thus nourishes primarily other shells. And it kills its prey by contact. It can, in its attack, to plant a true gust of arrows, many teeth radulaires, which in general measure some tenth of millimetres length and are held in reserve in a bag of the same name. Jointly, it holds its boor supported on the soft parts of its prey, which it devours then goulûment. Specify, which shows at which point the system cones is worked out, that after each expulsion, whereas a new tooth passes in its turn in the pharynx, in same time the poison gland contracts, poisonous secretion also passes it in the pharynx. It is there, then, which is filled the hollow tube with this tooth.
The dangerosity of the cones is known for a long time. It is known that they can cause dead of man. Thus, for the only News-Calédonie, in 1963, in Poindimié on the East coast of the Large-Ground, a young girl and an adult were victims of Conus geographus; it was the case also, in April 1975, of a 8 year old young girl, pricked by the shell which it had just collected. One counts some thirty fatalities in the world. The clinical table is more alarming. The area of the puncture inflates then very quickly and a feeling of dizzy spell extends to the whole body, involving a paralysis and death in the hour which follows. There is not any vaccine. Although to a lesser extent, the textile cone is him also dangerous for the man.
In a general way, the venom of the family of the cones has a remarkable diversity of active substances. It is a liquid blanchâtre container of small insoluble granules. As specify it Bernard Métivier and Stéphane Baghdiguian (Natural history museum): " venoms of cones act mainly on the transmission neuromusculaire and the ionic channels membrane. As for the majority of venoms, the first function of these toxins is to immobilize the preys by paralysing their muscles (5) ". These venoms, which contain in particular conotoxines, were, independently them noxious capacity, actively studied by pharmaceutical industry as from the years 1990. It was even made a specific request for conotoxines, whereas other animals secrete similar products. The advantage of toxins of cones is due indeed to their small size. A venom of snake, for example, consists of 60 to 80 amino acids. Certain toxins of spiders comprise up to 1 000 amino acids. The conotoxines show on the other hand seldom more than thirty of these acids, which makes them easier to synthesize by the biochemists.
An American firm (Neurex, Menlo Park California - now taken over by Elan Pharmaceuticals) is in the final stages of clinical tests of one of these conotoxins, baptized SNX-111 or Ziconotide, and synthesized in 1993, preliminary to being able to market it as an analgesic. SNX-111 is 100 to 1 000 times more powerful than morphine (6). More than one hundred of these conotoxins are currently being studied throughout the world and experiments are in hand which could provide drugs against certain forms of epilepsy and traumatic brain injury (7).
(2) Laboratoire de biologie et de biochimie mar in e de La Rochelle ; D. Röckel, G. Richard, R.B. Moolenbeek, in P. Bouchet (ed.), Mémoires du MNH, 167, 557, 1995.
(3) Manuel of the Living Conidae , vol. 1, Verlag Christa Hemmen, Wiesbaden, 1995.
(4) The Algorithmic Beauty of Sea Shells , Springer Verlag, Berlin, 2e édition, 1998.
(5) M. Goyffon, J. Heurtault (eds), La F onction venimeuse , Editions Masson, 1995, p. 46.
(6) J. Ramachandran, " Perspectives in Medical Chemistry ", B. Testa, E. Kybubs, W. Fuhrer, R. Gieger (eds), V CH, New York, 1993, p. 375.
(7) D. Concar, " Doctor snails ", New Scientist , 19/10/1996, p. 26 ; W.R. Gray, B.M. Olivera, L.J. Cruz, " Peptides toxins from venomous Conus Snails ", Annual Review of Biochemistry , 57 , 665, 1988; B.M. Olivera et al. , " Diversity of Conus neuropeptides ", Science , 249, 257, 1990.
La Recherche a publié :
(I) P. Coullet, " Le pendule et le coquillage ", et P. De Kepper et al ., " Taches, rayures et labyrinthes ", janvier 1998.
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