Machaerid
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Machaerids are a little-studied class of fossil animals. They are known from the Ordovician to the early Permian. They are segmented and rather worm-like with body armor made of hollow spines sclerites. Classically, they have been regarded as echinoderms or possibly descendants of echinoderm ancestors. Some authors have proposed that the Machaerids might be aberrant barnacles -- (arthropods). It is also possible that the Machaerids might be related to a rather poorly defined group of early Cambrian animals that do not resemble each other or anything else except in the fact that they have sclerites. These include Halkeria (an armoured worm), Wiwaxia (a much different armoured worm), and the sponge-like Chancelloria.