They are relatively common in Silurian and Devonian Lagerstätten, to which they are generally restricted due to their unmineralized cuticle [ 3 ], and have a total range extending from the mid-Ordovician until the end-Permian, throughout which time they exhibited a euryhaline distribution, with an increasing trend towards freshwater habitats apparent through the Carboniferous and Permian [ 4 ].
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