Gastrotricha
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Gastrotrich, group of microscopic wormlike animals that are common in aquatic environments worldwide. The gastrotrich lives in bottom sediments and on the surface of submerged vegetation and debris. Its head is divided into lobes and its body is generally flat, transparent, and unsegmented. Its back and sides are spiny, bristly, or scaly. The flattened bottom surface bears small hairs, or cilia, in characteristic patterns that are helpful in classifying species. Along the sides of the body are adhesive tubes that are used for clinging to vegetation.
Gastrotrichs range in length from 0.05 to 4.0 mm (0.002 to 0.16 in). Marine gastrotrichs, those living in the ocean, are abundant on the surfaces of corals and in shallow sandy areas, while freshwater species prefer standing water such as puddles, marshes, and wet bogs. They may be present in habitats where there is much decay and they can withstand low levels of dissolved oxygen for short periods. The gastrotrich feeds as it moves, ingesting bacteria, algae, small protozoans, and organic debris from the substrate. Waving cilia on the head create currents that push food particles to the mouth.
Marine gastrotrichs are hermaphroditic (having both male and female sex organs) and individuals alternately produce eggs and sperm. Most freshwater species are entirely female and reproduce through parthenogenesis (egg development without fertilization). A female will produce one to five very large eggs in its lifetime. The eggs are of two types: thin-walled eggs that develop as soon as they are laid, and thick-walled eggs that require exposure to harsh conditions such as drying, freezing, or high temperatures before they develop. Gastrotrichs have no larval stages. On emergence from the egg, the gastrotrich is already about 25 percent of its adult size. It grows rapidly and some species reach sexual maturity in only three days. The lifespans of gastrotrichs in nature are unknown, but individuals in laboratory cultures live 3 to 22 days. Gastrotrichs are important as food for many organisms in aquatic food webs.
Scientific classification: Gastrotrichs make up the phylum Gastrotricha, which contains two orders. Animals in the order Macrodasyida are strictly marine, and those in the order Chaetonotida are primarily freshwater.
Gastrotrichs range in length from 0.05 to 4.0 mm (0.002 to 0.16 in). Marine gastrotrichs, those living in the ocean, are abundant on the surfaces of corals and in shallow sandy areas, while freshwater species prefer standing water such as puddles, marshes, and wet bogs. They may be present in habitats where there is much decay and they can withstand low levels of dissolved oxygen for short periods. The gastrotrich feeds as it moves, ingesting bacteria, algae, small protozoans, and organic debris from the substrate. Waving cilia on the head create currents that push food particles to the mouth.
Marine gastrotrichs are hermaphroditic (having both male and female sex organs) and individuals alternately produce eggs and sperm. Most freshwater species are entirely female and reproduce through parthenogenesis (egg development without fertilization). A female will produce one to five very large eggs in its lifetime. The eggs are of two types: thin-walled eggs that develop as soon as they are laid, and thick-walled eggs that require exposure to harsh conditions such as drying, freezing, or high temperatures before they develop. Gastrotrichs have no larval stages. On emergence from the egg, the gastrotrich is already about 25 percent of its adult size. It grows rapidly and some species reach sexual maturity in only three days. The lifespans of gastrotrichs in nature are unknown, but individuals in laboratory cultures live 3 to 22 days. Gastrotrichs are important as food for many organisms in aquatic food webs.
Scientific classification: Gastrotrichs make up the phylum Gastrotricha, which contains two orders. Animals in the order Macrodasyida are strictly marine, and those in the order Chaetonotida are primarily freshwater.
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