Daphnia Anatomy
General Description
Daphnia are kidney-shaped organisms that contain a single compound eye, one double-branched antenna, and leaf-like limbs inside of the carapace, the exoskeleton of the daphnia, that produce a current to water that carries food and oxygen to different body parts of daphnia. Daphnia are semi-transparent, enabling the sight of the heart beating and other organs under a microscope. A carapace, or an exoskeleton, covers the whole body of the daphnia, including its brood chamber. Daphnia swim by rapid downward strokes of the second large antenna, as illustrated in the diagram. The thoracic appendages are the leaf-like limbs that produce a constant current of water. The thoracic appendages also filter out small particles (less than 50 microns in diameter) in the water by fine setae on the thoracic legs and moved along a groove at the base of legs to the mouth.
The diagram on the left outlines more body parts and functions of daphnia. |
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Male vs Female
Male daphnia are usually distinguished from female daphnia by their smaller size, larger antennas, modified post-abdomen, and first legs, which are armed with a hook used in clasping. Female daphnia also contain a brood chamber with eggs, while males do not.
The slideshow on the left displays some visual differences between male and female daphnia. Notice that the daphnia in the black background has small yellow eggs, while the daphnia in the brown background does not. |
Life Span and Life CycleDaphnia lifespan is usually very short and heavily dependent on temperature and environment. In general, in the case of daphnia, the life span increases as the temperature decreases, due to lowered metabolic activity. The average life span of D. magna is about 40 days at 25 degrees Celsius and about 56 days at 20 degrees Celsius .
The life cycle of daphnia can illustrated in four main steps: egg, juvenile, adolescent, and adult. First, in the egg stage, six to ten eggs are released into the brood chamber and are hatched there as juveniles. The juveniles are released out of the female body when the female molts her exoskeleton, typically two days after the hatching. At that stage the juveniles are almost already similar in form to adults. Finally, after six to ten days, the juveniles become adults and reach maturity. |