| Uaru |
the waroo to triangle cichlid of the Amazon and Guyana,
U. amphiacanthoides, a beautiful schooling species that is maintained
with some difficulty by specialized aquarists |
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| Udotea |
green marine algae with a calcified skeletal structure giving it
the shape of a fan emerging from the substrate |
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| Ultraviolet light |
(UV) electromagnetic radiation with a wavelength between 100 and
380 nanometers |
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| Ultraviolet sterilization |
elimination of microorganisms from water by exposure to ionizing
light radiation one of the oldest portions of the shell of a mollusk |
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| Umbra |
mudminnows, Family Umbridae, native to North America and Eurasia;
maintained successfully by aquarium hobbyists but rare and considered
extinct in some portions of its natural range |
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| Undergravel filter |
a device for enhancing bacterial nitrification in the substrate
of an aquarium, consisting of a perforated plate upon which substrate
is layerd, through which water is drawn and expelled near the surface
of the tank by various methods |
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| Undulipodium |
the long, whip-like locomotory organelle of a eukaryotic cell, synonymous
with flagellum in common usage; the latter term is reserved by microbiologist
for the functionally similar structure of a prokaryotic cell |
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| Urogenital opening |
the common outlet of the excretory and reproductive systems in fish |
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| Uropod |
the flattened blades of the sixth abdominal appendage of crustaceans,
together with the telson forming a tail fin |
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| Utricularia |
bladderworts, freshwater flowering plants of temperate, tropical,
and subtropical America with tiny bladders that trap microinvertebrates;
maintained in aquariums and garden ponds as a curiosity |
