Hallucigenia

The hallucigenia is a extinct kind of animal which one found the Fossile S in the formations of the average Cambrien of the Schistes of Burgess in Colombia-British. It was named by Simon Conway-Morris when it re-examined the kind Canadia found in the schists of Burgess by Charles Doolittle Walcott in 1979. Morris discovered that what Walcott identified as being only one kind contained in fact some extremely different animals. One of them was so unusual that nothing about it had apparently direction. Since the animal was certainly not a worm polychète, Morris had to provide a new name to the creature to replace Canadia . He thus chooses the name of hallucigenia because of the " strange and whimsical qualities seeming left a rêve" animal (like a hallucination).

The body from 0.5 to 3 cm length is long and thin, such that of a worm, with a spot badly defined at an end. It was indicated arbitrarily as being the " tête" , though not having any characteristic of a head itself, namely a mouth, eyes or other sensors. The animal has seven tentacles ending in " pinces" , aligned on a side and seven pairs of spines united of the other. There is moreover six tentacles smaller which can be configured in three pairs behind seven larger. There is moreover one soft tubular extension of the body behind the tentacles.

Confronted with an animal not having nor clearly defined head and two types of appendices, none of both not seeming suited to the locomotion, Morris indicated the spot like the head and supposed that the spines were legs and the tentacles of the feeder appendices. It could moreover show a functional way though not very probable of locomotion on the spines. Only the tentacles in front of the body can join the " easily; tête" , meaning that mouth located on the latter would require that the food passed from one tentacle to the other to nourish it. This is why it suggested that a hollow tube in each tentacle could act as mouth. The rebuilding is very little satisfactory, but it nevertheless was accepted, being the best available one. The rebuilding of Morris can be found here: (page in English) .

An alternative interpretation supported by some paleontologists was that hallucigenia is in fact the appendix of a larger animal. Considering the uncertainty of its taxonomy, it was arranged among the lobopodes, a Clade containing several strange " worms with pattes".

In 1991, Ramiskold and Hou Xianguang, working with additional specimens of a " hallucigénide" Schistes of Maotianshan Chinese reinterpreted the hallucigenia as being a onychophore. They reversed it, interpreting this time the tentacles, which they believe outward journey of par, like structures adapted to walk, the spines constituting a protection. Interesting fact, none of some 30 specimens found in the schists of Burgess shows any index of pairs of the large tentacles; their counterparts Chinese either, moreover. The theory of the pair is based on a dissection of the one of the fossils, which reveals what is probably a second tentacular structure. Ramiskold and Hou believe that the spot earlier interpreted as being a head is indeed only one spot which appears at several specimens and not an anatomical part preserved by fossilization.

Though their theory is that generally accepted today, it is far from being stripped of problems. Contrary to its contemporary, the Aysheaia, the hallucigenia presents only few resemblances to the modern onychophores. The tentacles potentially in pairs resemble very little the ringed legs of the onychophores. Nobody knows yet what the spines were done, nor moreover which degree of protection they could offer. They never seem to be preserved independently of the animals with soft body like a shell of Chitine or of Carbonate would probably do it. It is difficult to explain why about thirty specimens, which have seven pairs long hypothetically and flexible legs, do not show any example of pairs of legs. At least, this reconstitution of the animal can go in a plausible way and the spines have a reasonable utility. An image of this new reconstitution just as a photograph of fossil are with. (page in English)

Certain paleontologists accept the interpretation of Hou and Ramiskold, but believe that the animal could be a " lobopode with armure" connected with the Anomalocaris rather than (or while being) to be related with the onychophores. The possibility that hallucigenia is only part of a larger animal, as for it, is not excluded.

Stephen Jay Gould, a popularizer who often quoted this fossil

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