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 Daphnia magna with eggs
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Daphnia are small, mostly planktonic, crustaceans, between . Plankton consist of any drifting Organisms ( Animals Plants Archaea, or Bacteria) that inhabit the Pelagic zone of Structure of crustaceans As Arthropods crustaceans have a stiff Exoskeleton, which must be shed to allow the animal to grow ( Ecdysis or molting 2 and 5 mm in length. The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style (although fleas are insects and thus only very distantly related). This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used Cladocera or cladocerans are small Crustaceans commonly called Water fleas, part of the Class Branchiopoda. Water flea is a generic term for a number of small aquatic Crustacea characterised by their jumping or jerky mode of swimming Flea is the Common name for any of the small wingless Insects of the order Siphonaptera (some authorities use the name Aphaniptera Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described They live in various aquatic environments ranging from acidic swamps to freshwater lakes, ponds, streams and rivers. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are A swamp is a Wetland featuring temporary or permanent inundation of large areas of land by shallow bodies of water Freshwater is a word that refers to bodies of water such as Ponds lakes rivers and streams containing low concentrations of dissolved Salts and other Total dissolved
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Biology
The division of the body into segments is nearly invisible. Segmentation in biology refers to the division of some Metazoan bodies and Plant body plans into a series of semi-repetitive segments and the question of The head is fused, and is generally bent down towards the body with a visible notch separating the two. In most species the rest of the body is covered by a carapace, with a ventral gap in which the five or six pairs of legs lie. A carapace is a dorsal section of an Exoskeleton or shell in a number of animal groups The most prominent features are the compound eyes, the second antennae, and a pair of abdominal setae. Antennae (singular antenna) are paired Appendages connected to the front-most segments of Arthropods In Crustaceans they are Seta (plural setae) is a biological term derived from the Latin word for " Bristle " In many species, the carapace is translucent or nearly so and as a result they make excellent subjects for the microscope as one can observe the beating heart. A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are
Even under relatively low power, it is possible to observe the feeding mechanism working, watch immature young moving in the brood-pouch, observe the eye being moved by the ciliary muscles and even watch blood corpuscles being pumped round the circulatory system by the simple heart. The Ciliary Muscle is a muscle in the eye that controls the eye's accommodation for viewing objects at varying distances This is an article about the rock music band "Circulatory System" The heart is at the top of the back, just behind the head, and their average heart rate is approximately 180bpm under normal conditions. Daphnia, like many animals, are prone to alcohol intoxication, and make excellent subjects for studying the effects of the depressant on the nervous system – due to the translucent exoskeleton, and the visibly altered heart rate. The nervous system is a Network of specialized cells that communicate information about an animal's surroundings and itself Measuring heart rate The Pulse rate (which in most people is identical to the heart rate can be measured at any point on the body where an Artery 's pulsation They are tolerant of being observed live under a cover slip and appear to suffer no harm when returned to open water. This experiment can also be done using caffeine, nicotine or adrenaline and observing an increase in heart rate. Caffeine is a bitter white crystalline Xanthine Alkaloid that acts as a Psychoactive Stimulant Drug and a mild Diuretic Nicotine is an Alkaloid found in the Nightshade family of plants ( Solanaceae) which constitutes approximately 0
A few Daphnia prey on tiny crustaceans and rotifers, but most are filter feeders, ingesting mainly unicellular algae and various sorts of organic detritus including protists and bacteria. Structure of crustaceans As Arthropods crustaceans have a stiff Exoskeleton, which must be shed to allow the animal to grow ( Ecdysis or molting The rotifers make up a Phylum of microscopic and near-microscopic pseudocoelomate Animals They were first described by Rev Filter feeders (also known as suspension feeders) are Animals that feed by straining suspended matter and food particles from water typically by passing the water Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have They also eat forms of yeast, but mostly in laboratories or controlled environments. Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described Daphnia can be kept easily on a diet of yeast. Beating of the legs produces a constant current through the carapace which brings such material into the digestive tract. The trapped food particles are formed into a food bolus which then moves down the digestive tract until voided through the anus located on the ventral surface of the terminal appendage. The first and second pair of legs are used in the organisms' filter feeding ensuring large unabsorbable particles are kept out while the other sets of legs create the stream of water rushing into the organism. Swimming, on the other hand, is powered mainly by the second set of antennae which are larger in size than the first set. The action of this second set of antennae is responsible for the jumping motion. Certain scientific studies have proved that even though it seems to fit into the kingdom Protista as a protist,it actual has the charateristics of a living animal,therefore it belongs to the kingdom Animalia.
Reproduction
Daphnia reproduce parthenogenetically usually in the spring until the end of the summer. Parthenogenesis (from the Greek παρθένος parthenos, "virgin" + γένεσις genesis, "creation" is an asexual form One or more juvenile animals are nurtured in the brood pouch inside the carapace. The newly hatched Daphnia must moult several times before they are fully grown into an adult usually after about two weeks. The young are small copies of the adult; there are no true nymphal or instar stages. In Biology, a nymph is the immature form of some Insects which undergoes incomplete metamorphosis ( Hemimetabolism) before reaching its adult An instar is a developmental stage of Arthropods, such as Insects, between each moult ( ecdysis) until sexual maturity is reached The fully mature females are able to produce a new brood of young about every ten days under ideal conditions. The reproduction process continues while the environmental conditions continue to support their growth. When winter approaches or in drought conditions or at times of other harsh environmental conditions, production of new female generations cease and parthenogenic males are produced. However, even in harsh environmental conditions males may make up considerably less than half the population, in some species they are unknown entirely. Males are much smaller in size than the female and they typically possess a specialised abdominal appendage which is used in mating to grasp a female from behind and prise open her carapace and insert a spermatheca and thus fertilise the eggs. An appendage in the broadest sense is an additional or subsidiary part existing on or added to something which can generally still function if the appendage has never existed or A carapace is a dorsal section of an Exoskeleton or shell in a number of animal groups The spermatheca (plural spermathecae) is an organ of the female reproductive tract in Insects some Mollusks and certain other Invertebrates These fertilised eggs are termed winter eggs and are provided with extra shell layer called ephippium. Bulbophyllum is the largest genus in the orchid family Orchidaceae. The extra layer preserves and protects the egg inside from harsh environmental conditions until the more favourable times, such as spring, when the reproductive cycle is able to take place once again.
In addition to the production of eggs capable of overwintering, this switch to sexual reproduction has also been proposed to allow greater offspring variation (through genetic recombination) which may be useful in varied or unpredictable conditions, this idea is often proposed under the name of the lottery model
Lifespan
The lifespan of a Daphnia does not exceed one year and is largely temperature dependent. For example, individual organisms can live up to 108 days at 3°C while some organisms live for only 29 days at 28°C. The Celsius Temperature scale was previously known as the centigrade scale. A clear exception to this trend is during the winter time in which harsh conditions limit the population in which females have been recorded to live for over six months. These females generally grow at slower rate but in the end are larger than ones under normal conditions.
Uses
Sometimes Daphnia may be used in certain environments to test the effects of toxins on an ecosystem. A toxin ( Greek:, toxikon, lit (poison for use on arrows is a Poisonous substance produced by living cells or organisms that is active at very low An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( This makes Daphnia an indicator species, particularly useful in that area because of its short lifespan and reproductive capabilities. An indicator species is any Biological species that defines a trait or Characteristic of the environment
Ecology
The populations of several water flea species are considered threatened. The following are listed as vulnerable by IUCN: Daphnia nivalis, Daphnia coronata, Daphnia occidentalis, and Daphnia jollyi.
External links
- Daphnia Genomics Consortium
- Daphnia Images and Information at MBL Aquaculture
- Daphnia: An Aquarist's Guide
- Waterflea.org: a Community resource for cladoceran biology
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