<P> Whittington's first presentation about Opabinia made the audience laugh . The reconstruction showed a soft - bodied animal with a slim, segmented body; a pair of flap - like appendages on each segment with gills above the flaps; five stalked eyes; a backward - facing mouth under the head; and a long, flexible, hose - like proboscis that extended from under the front of the head and ended in a "claw" fringed with spines . Whittington concluded that it did not fit into any phylum known in the mid-1970s . Opabinia was one of the main reasons why Stephen Jay Gould in his book Wonderful Life considered that Early Cambrian life was much more diverse and "experimental" than any later set of animals, and that the Cambrian explosion was a truly dramatic event, possibly driven by unusual evolutionary mechanisms . He regarded Opabinia as so important to understanding this phenomenon that he originally wanted call his book Homage to Opabinia . However subsequent research has concluded that Opabinia is closely related to the arthropods and possibly even closer to ancestors of the arthropods . </P> <P> The discovery of Anomalocaris ("abnormal shrimp") was a comedy of errors . The name was initially given to a fossil that looked like the rear end of a shrimp - like crustacean . Walcott classified a ring - like fossil he called Peytoia as a kind of jellyfish, and another poorly preserved fossil he called Laggania as a holothurian (sea cucumber). After many plot twists, Derek Briggs started dissecting another ill - defined fossil in very thin slices and found a pair of Anomalocaris - like structures on one end of a specimen of Laggania, which also had a specimen of Peytoia attached just behind those of Anomalocaris . After dissecting more specimens and finding similar configurations, Briggs and Whittington concluded that the whole assemblage represented a single animal, which was named Anomalocaris because that was the earliest name assigned to any of its parts . This animal's body was fragile and usually disintegrated before it could be fossilized . But the complete animal had tough grasping appendages (Anomalocaris), a tough, ring - like mouth with teeth on the inner edge (Peytoia) and a long, segmented body (Laggania) with flaps on the sides that enabled it to swim with a Mexican wave motion, and perhaps to turn quickly by putting the flaps on one side into reverse . This monster was over 2 feet (0.61 m) long when other animals were only a few inches at most . Nedin suggested in 1999 that the animal was capable of taking heavily armored trilobites apart, possibly by grabbing one end of their prey in their jaws while using their appendages to quickly rock the other end of the animal back and forth, causing the prey's exoskeleton to rupture and allowing the predator to access its innards . In 2009 Hagadorn found that anomalocarid mouthparts showed little wear, which suggests they did not come into regular contact with mineralised trilobite shells . Computer modeling of the Anomalocaris mouthparts suggests they were in fact better suited to sucking on smaller, soft - bodied organisms . Although Whittington and Briggs concluded that Anomalocaris did not fit into any known phylum, research since the 1990s has concluded that it was closely related to Opabinia and to the ancestors of arthropods . In 2009 a fossil named Schinderhannes bartelsi, an apparent relative of Anomalocaris, was found in the Early Devonian period, about 100 million years later than the Burgess Shale . Conway Morris gave Hallucigenia its name because in his reconstruction it looked bizarre--a worm - like animal that walked on long, rigid spines and had a row of tentacles along its back . Science fiction author Greg Bear says the Jarts in his The Way stories were scaled - up versions of this reconstruction . However, in the late 1980s Lars Ramsköld literally turned it over, so that the tentacles, which he found were paired, became legs and the spines were defensive equipment on its back . Ramsköld classified it as one of the Onychophora, a phylum of "worms with legs" that is considered closely related to arthropods . Another current view is that Hallucigenia was an armored lobopod, in other words more closely related to arthropods than the onychophorans are, but less closely related to arthropods than Opabinia or Anomalocaris are . </P> <P> Most fossils of Wiwaxia are just a jumble of armor plates and spines, but after examining dozens of them Conway Morris reconstructed them as slug - like animals covered in rows of overlapping armor plates, with two rows of longer spines projecting upwards . Since 1990 there has been an intense debate about whether Wiwaxia was more closely related to molluscs or to polychaete annelids . Supporters of a close relationship with molluscs maintained that a pair of bars, running across the mouth and armed with backward - pointing teeth, were a rudimentary form of the radula, the toothed tongue that molluscs use to scrape up food and convey it back to the throat . Nicholas Butterfield, the one academic who has so far published articles placing Wiwaxia closer to polychaetes, stated that Wiwaxia ′ s two - row feeding apparatus could not have performed the sophisticated functions of the multi-row, conveyor - belt radula, suggesting instead that Wiwaxia ′ s apparatus was like the side - by - side pair of toothed bars found in some polychaetes . Later he found some fragmentary fossils, 5 to 10 million years before the Burgess Shale, that he regarded as a much more convincing early radula . Butterfield has also described Wiwaxia ′ s armor plates and spines as similar in internal structure to the chetae ("hairs") of polychaetes . Supporters of the link with molluscs have stated that Wiwaxia shows no signs of segmentation, appendages in front of the mouth, or "legs---- all of which are typical polychaete features . One writer adopted a neutral position, saying he saw no strong grounds for classifying Wiwaxia as a proto - annelid or a proto - mollusc, although he thought the objections against classification as a proto - annelid were the stronger . </P> <P> For many years Odontogriphus ("toothed riddle") was known from only one specimen, an almost featureless oval smear on a slab, with hints of tiny conical teeth . However, 189 new finds in the years immediately preceding 2006 made a detailed description possible . It had a pair of slightly V - shaped tooth - rows just ahead of the mouth, very like Wiwaxia ′ s . This pitched Odontogriphus into the middle of the debate about whether Wiwaxia was closer to the mollusc or the annelid lineage, resulting in a frank exchange of views . </P>

What are the predominant types of organisms found in the burgess shale