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Holochroal eye: found in nearly all Orders few to very many lenses (to >15,000!) lenses typically small, numerous one corneal layer covers all lenses lenses in direct contact with others no sclera between lenses corneal membrane covers surface only. Schizochroal eye: found in some Phacopida only typically fewer lenses (to ca 700) lenses much larger, fewer each lens bears an individual cornea lenses separated from each other sclera between lenses very deep corneal membrane extends into sclera. Abathochroal eye: found in Cambrian Eodiscina only few lenses (to ca 70) lens size small, not numerous each lens bears an individual cornea lenses separated from each other interlensar sclera not deeper than lenses corneal membrane ends at lens margin. All early trilobites (Cambrian), had holochroal eyes and it would seem hard to evolve the distinctive phacopid schizochroal eye from this form. The answer is thought to lie in ontogenetic (developmental) processes on an evolutionary ...

Most people realise that reconstructions of animals from their fossilised remains is a risky business, and that when there are only a few fossil specimens, opportunities for misinterpretation are many. Add to this an investigator who declares `I have a natural temptation to emphasise the unusual', then the probability of error is greatly increased. All these ingredients are present in the case of an organism named Hallucigenia, first described in 1977 by Conway Morris in the journal Palaeontology. However, new evidence has come to light which suggests that Hallucigenia exists only in our imagination. Lars Ramiskold of the Swedish Museum of Natural History and Hou Xianguang from the Nanjing Institute of Geology and Palaeontology have been studying worm-like fossils from Southern China. They consider that the fossils have a body plan similar to the velvet worms of modern rain forests, but that they were armoured - bearing protective spines. After comparing the characteristics of...

Hallucigenia is an extinct genus of animal found as fossils in the Middle Cambrian-aged Burgess Shale formation of British Columbia, Canada. It was named by Simon Conway Morris when he re-examined Charles Walcott's Burgess Shale genus Canadia in 1979. Conway Morris found that what Walcott had called one genus in fact included several quite different animals. One of them was so unusual that nothing about it made much sense. Since the species clearly was not a polychaete worm, Conway Morris had to provide a new generic name to replace Canadia. Conway Morris named the species Hallucigenia sparsa because of its "bizarre and dream-like quality" (like a hallucination). When originally discovered and prepared, fossils of the animal Hallucigenia appeared to have preserved two rows of spines on one side of the animal and one row of tentacles on the other. Identifying its head was a problem - the fossil showed only a rounded, dark stain at one end and a narrower, dark stain at ...

"The peninsula Avalon in Newfoundland is separated by 4000 km of ocean from legendary Avalon in Wales. Trilobites show that the two Avalons were conjoined half a billion years ago. Fortuitous congruence of names? Or the influence of the Arthurian magician Merlin?"