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Daphnia Research Paper

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Daphnia are small planktonic crustaceans that belong to the Phyllopoda (sometimes called Branchiopoda), which are characterized by flattened leaf-like legs used to produce a water current for the filtering apparatus. Within the branchiopods, Daphnia belong to the Cladocera, whose bodies are enclosed by an uncalcified shell known as the carapace. It has a double wall, between which hemolymph flows and which is part of the body cavity. The carapace is largely made of chitin, a polysaccharide. Cladocera have up to 10 pairs of appendages, which are (from front to back): antennules, antennae (the second antennae, used for swimming); maxillae; and mandibles; followed by 5 (as in Daphnia) or 6 limbs on the trunk. The limbs form an apparatus for …show more content…
There are two small digestive ceca(diverticula) that are easily seen in the head section of the midgut. The midgut is lined with an epithelium and bears microvilli. Peristaltic contractions of the gut wall pass food through the gut, but a peritrophic membrane contains the food and prevents it from entering the ceca. Epithelial cells do not phagocytose particles but absorb molecules. The pH is 6 to 6.8 in the anterior part of the midgut and 6.6 to 7.2 in the posterior part. Food is expelled from the hindgut by peristaltic movement but also requires the pressure of more recently acquired food particles. The color of Daphnia adapts to the food that is predominant in their diet. Daphnia feeding on green algae will be transparent with a tint of green or yellow, whereas those feeding on bacteria will be white or salmon-pink. Well-fed animals are more strongly colored than starved animals. Daphnia have an open blood circulation. The heart is located dorsally and anterior from the brood chamber. At 20ºC, it beats about 200 times per minute, slowing down at lower temperatures. Blood cells are easily visible through the transparent body as they flow rapidly through the body cavity. To support oxygen transport, Daphnia have the extracellular respiratory protein hemoglobin (Hb), a multi-subunit, multi-domain macromolecule. There are at least four Hb genes. Daphnia tend to develop more Hb to …show more content…
This behavior stems from the beating of the large antennae, which they use to direct themselves through the water. The rapid downbeat produces a quick upward movement, whereas the relatively high density of the animals creates a sinking. Motionless Daphnia sink rapidly to the ground.
A second well-known behavior of Daphnia is diel vertical migration, in which they migrate toward upper levels of the water body during nighttime and then back downward during the early morning and daytime. This behavior probably developed as a predator avoidance strategy. During daylight, the Daphnia hide from fish that hunt visually by moving to darker depths, whereas during nighttime, they take advantage of the richer food (planktonic algae) in the well-illuminated upper water levels. Inverse diel vertical migration has been described as a strategy to escape other predators that migrate

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