Sea fleas (Lat: Podonidae) belong to an order of small-bodied crustaceans also known as Cladocera in Latin. While the majority of water flea species live in fresh water, there are about eight species that live in oceans, especially in coastal areas or in seas that are relatively closed, with an abundant supply of sweet water. These small creatures are very exciting, especially as they are able to survive even the harshest of climatic or weather conditions.
Sea fleas are small, their size ranging between 0.2-6 mm. The characteristic shape features a small, downward-angled head and a body that seems unsegmented as it is covered integrally by the carapace. Under the shell, the body is segmented, with a visible division line between the abdomen and the thorax. Most species have one compound eye and one ocellus, that is, a simple eye as well. The head also has a pair of unsegmented, smaller antennae and another pair that is longer, segmented, with powerful muscles used for swimming.
The mouth of sea fleas is also small, even compared to their body size, but very complex, consisting of mandibles, maxillae, labium and labrum. The thorax of the sea flea is also compound, being divided into 5-6 haired appendages.
The majority of sea flea species reproduce in both sexual and asexual ways. The choice of the reproduction method depends on the quality of living conditions – among favorable conditions, the preferred mode of reproduction is parthenogenesis, that is, asexual reproduction, with exclusively female off springs. Males appear only when living conditions become unfavorable. In these periods, the pairs of fleas start producing eggs that can lay dormant for years that are carried by the wind and start developing and hatching only when they reach a territory with more favorable living conditions.
Water fleas, including the species that live on or around the sea, are filter feeders, striving on algae and detritus of various types. Podonidae feed by making water currents with their legs, currents which bring nutrients to the animal’s digestive tract.
Even though the water fleas striving around salt water are among the smallest living beings on earth, they are also among the most populous and oldest species. There are numerous flea species that have already been catalogued, but scientists still have a long way to go until they can say the incredible world of sea fleas has been properly mapped.