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Water flea

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== Reproduction ==
== Reproduction ==
Daphnia can produce either sexually or asexually. Most of the Daphnia in a colony are female. This is because, when conditions are right, a Daphnia  will produce more females than males. When conditions are poor she will produce about an equal amount of males and females.[http://lawrencehallofscience.org/foss/fossweb/teachers/materials/plantanimal/daphnia.html] The female Daphnia has a brood pouch in which eggs and embryos are held until birth. [http://www.science.mcmaster.ca/Biology/Harbour/SPECIES/DAPHNIA/DAPHREPR.HTM] There are different kinds of eggs in the brood pouch. One is Summer eggs which develops parthenogenetically, has little yoke, and doesn't need to be fertilized. Summer eggs are very numerous and are usually not released until they are sexually mature or maybe even have young of their own. Second are resting eggs which have a lot of yoke, a thick shell, and can only produce after being fertilized. There are only two resting eggs (one from each ovary) that are released into the brooding chamber as well. Third there are winter eggs which are released instantly either naked or in a protected cuticular ephippium. How they are released depends on taxon. The eggs are held inside the Daphnia for only a few days before a new generation of Daphnia are born. [http://webs.lander.edu/rsfox/invertebrates/daphnia.html]
Daphnia can produce either sexually or asexually. Most of the Daphnia in a colony are female. This is because, when conditions are right, a Daphnia  will produce more females than males. When conditions are poor she will produce about an equal amount of males and females.[http://lawrencehallofscience.org/foss/fossweb/teachers/materials/plantanimal/daphnia.html] The female Daphnia has a brood pouch in which eggs and embryos are held until birth. [http://www.science.mcmaster.ca/Biology/Harbour/SPECIES/DAPHNIA/DAPHREPR.HTM] There are different kinds of eggs in the brood pouch. One is Summer eggs which develops parthenogenetically, has little yoke, and doesn't need to be fertilized. Summer eggs are very numerous and are usually not released until they are sexually mature or maybe even have young of their own. Second are resting eggs which have a lot of yoke, a thick shell, and can only produce after being fertilized. There are only two resting eggs (one from each ovary) that are released into the brooding chamber as well. Third there are winter eggs which are released instantly either naked or in a protected cuticular ephippium. How they are released depends on taxon. The eggs are held inside the Daphnia for only a few days before a new generation of Daphnia are born. [http://webs.lander.edu/rsfox/invertebrates/daphnia.html]
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Males are a lot smaller than females and have an appendage in their abdomen which is used to hold the female from behind, pry open her carapace, in injects the sperm inter her winter eggs. [http://en.wikipedia.org/wiki/Daphnia#Reproduction]
== Ecology ==
== Ecology ==

Revision as of 21:33, 27 November 2009

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Water flea
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Scientific Classification
Families
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Image Description
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Contents

Introduction

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Anatomy

Description

Daphnia are very small kidney shaped creatures in the water.For sight they have a single compound eye. They also have two doubly branched antennae, and leaf like limbs which make a current inside the carapace that allows food and water to pass through it's gills. Their bodies are translucent, and under a microscope, you can see it's heart beating, and maybe even their last meal they are digesting.[1]

The Daphnia's internal structures are protected by a shell-like carapace which is only one piece even though it looks like two valves.[2] It is a double fold of the body wall stretching across the whole of the Daphnia's body like a little cape attached only to the neck. It's a large, thin, very flexible layer folded along the mid-line of the dorsal side of the water flea making two valves. The carapace is closed on its dorsal side, but at the posterior and ventral sides, the two valves are opened allowing water and food to pass through with the current.[3] At the posterior end of the Daphnia there are paired claws used for getting rid of unwanted particles between the carapace.[4]

Most of the rest of the Daphnia's body is in the thorax. It has five pairs of biramous, setose and thoracopods (appendages). Two pairs of these appendages make the current through which water and food may run. It draws water through a setal filter where it exits through the spaces the limbs. Food particles are stopped at the setal filter and moved to the ventral food groove where they move from appendage to appendage until it reaches the mouth. The food will travel down in to a "C" shaped intestine where it is decomposed and goes directly from the mouth to the anus. [5]


The water flea's circulatory system consists of a heart, hemocoel (basically the body cavity), and blood. A short, oval heart is at the dorsal end and is surrounded by hemocoel. This heart has only a single pair of ostia although it may not be evident, and no blood vessels are present. The heart forces blood to the hemocoel of the head. It then flows to the posterior end through three hemocoel chambers and then it will travel back to the heart. The Daphnia's carapace is the primary source of gas exchange.[6]

Reproduction

Daphnia can produce either sexually or asexually. Most of the Daphnia in a colony are female. This is because, when conditions are right, a Daphnia will produce more females than males. When conditions are poor she will produce about an equal amount of males and females.[7] The female Daphnia has a brood pouch in which eggs and embryos are held until birth. [8] There are different kinds of eggs in the brood pouch. One is Summer eggs which develops parthenogenetically, has little yoke, and doesn't need to be fertilized. Summer eggs are very numerous and are usually not released until they are sexually mature or maybe even have young of their own. Second are resting eggs which have a lot of yoke, a thick shell, and can only produce after being fertilized. There are only two resting eggs (one from each ovary) that are released into the brooding chamber as well. Third there are winter eggs which are released instantly either naked or in a protected cuticular ephippium. How they are released depends on taxon. The eggs are held inside the Daphnia for only a few days before a new generation of Daphnia are born. [9]

Males are a lot smaller than females and have an appendage in their abdomen which is used to hold the female from behind, pry open her carapace, in injects the sperm inter her winter eggs. [10]

Ecology

Description




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