The many species of daphnia are mostly found in fresh-water ponds. Daphnia range in size up to 4mm and are often transparent. Their beating heart, dark digestive tract and brood pouch with developing embryos can be seen. Modified antenna
serve as the swimming organs. Respiration occurs through body surfaces. They have a single compound eye and are continually eating free-floating algae. They have no larval stage, young leave the brood pouch as miniature adults.
Normally, females produce eggs without being fertilized by a male (parthenogenesis). When the pond begins to dry up or conditions otherwise become unfavorable, male daphnia develop from some of the eggs and the female start producing a
different 'resting' egg. These require fertilization by a male. The Daphnia's brood pouch changes and at the next molt, the old shell (carapace) and the enclosed eggs are shed. The embryos can withstand drying and freezing cycles while awaiting
for more favorable conditions to return.