Cheilostomata
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Cheilostomida, an order under class Gymnolaemata are small, colonial, aquatic invertebrate animals. Cheilostomida grow on surfaces of rocks and kelps. They have a "blind-ended", pouch-like gut, and no respiratory, circulatory, or nerve system. Individual members of the cheilostome colony are protected by a calcareous or chitinous covering that may be closed by a lidlike structure, an operculum. The cheilostomes are the most abundant and varied of modern bryozoans. The classification in suborders is based upon frontal calcification and the mechanism of lophophore protrusion.
[edit] Evolution
Cheilostomes first appeared in the Late Jurassic but diversified very slowly during the Early Cretaceous, with only 10 genera known from the Albian. During the Late Cretaceous, cheilostomes diversified rapidly to reach a level of 185 known genera in the Maastrichtian. Subsequently, they declined through the Palaeocene to a Thanetian diversity of 125 genera. After the Thanetian, they again diversified through much of the remaining Cenozoic, interrupted by a modest Oligocene reversal, apparently reaching a plateau of 240 to 250 genera during the Neogene.
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