Crustaceans - Large Branchiopoda
> Tanymastix stagnalis
Order: Anostraca (“fairy shrimp”)
Fairy-shrimps are temporary freshwater crustaceans adapted to very concrete conditions of the aquatic environment and with very strict tolerances to certain environmental factors and are, therefore, considered good ecological indicators.
They differ from the remaining Branchiopodes due to the lack of carapace. This temporary freshwater crustaceans can reach a maximum length of 1.5cm.
Crustaceans of the order Anostraca, have separated sexes but with a clear sexual dimorphism, that is, the males and the females have a different aspect. Males have retractable penis and antennas developed to grab the female during copulation. Females have smaller antennas and have a small globular ovissac (cystic sac) that rarely exceeds the 3rd abdominal somite. This bag of cysts is of reddish color with refringente central protuberance (from gold to metallic blue). It is in this ovissac that the eggs mature and are stored until their release. Next image shows a female with the bag of cysts.
Female of Tanymastix stagnalis. Photo of Luis Guilherme Sousa
Male of Tanymastix stagnalis. Photo of Luis Guilherme Sousa
These temporary freshwater crustaceans live in temporary ponds with few or no predators. One very interesting feature is that these fairy-shrimp swim freely with belly upwards through the body of water.
Movement, respiration and feeding are done together by toracopods beating which remove particles from the water column, such as phytoplankton, protozoa, organic debris or even clay particles because they have some organic matter in their composition. These foods accumulate in the alimentary canal and are pushed to the mouth with the help of the first toracopods.
The following image shows some details of the morphology of these animals.
The active stage of the life cycle takes place in the initial phase of flooding of the biotope, extending in optimum conditions until about 3 months.
They are filterers because they swim freely in the water column "filtering" what they find, such as phytoplankton, protozoa, organic debris or even clay particles because they have in their composition some organic matter that serves as food.
Fertilization is internal and female store the cysts in the ovissac until they're ready to release. The cysts are shaped like lentils with the flattened lip of reddish-brown color, are very visible in the ovissac.
The number of cysts per posture is directly related to the size of the female.
Freshwater temporary ponds, namely the Mediterranean Temporary Ponds (priority habitat 3170 - Directive 92/43/CEE).
Palearctic specie. In Portugal it was found in Minho, in the watershed of Tagus, in Lower and Higher Alentejo, and in Algarve, namely in the southwest coast, from Vila Nova de Milfontes until Vila do Bispo.
The threats to this species are directly related with the loss and degradation of its habitat. Up to this date it has no legal protection status.