Where do crabs go in winter
Habitats - In the brook
Towards the end of the last century, crayfish plague was introduced to Europe from North America, presumably with imports of live crabs. Within a few weeks, the cancer populations of entire water systems were eradicated. The disease is caused by the fungus Aphanomyces astaci. Only a few stocks were spared, were able to recover and spread. The American species are also attacked by the cancer plague pathogen, but the disease is not epidemic in them.
A white worm (Branchiobdella), a blood-sucking parasite that is several millimeters long (film!) Is often found on the joints, in the gills and on the eye stalks. Some of the parasites are stripped off during the moult.
The cancer has one Exoskeleton, which consists of lime-impregnated chitin and supports and protects the body. Head and chest are one Head chest piece (Cephalothorax) fused. A particularly hard shell arches over it as armor. A transverse furrow gives an idea of where the head and chest meet. The armor ends between those sitting on stalks Compound eyes with a tip, the so-called crab nose (rostrum). The areas to the left and right of the two longitudinal furrows cover the two gill cavities. The Abdomen (Abdomen) is clearly divided into five rings. All higher cancers originally consisted of 21 segments, each with a pair of limbs. In the crayfish, the limbs are adapted to their function: The first pair of antennas is not only an organ of smell, but also carries the organ of equilibrium in the base (1); the 2nd larger pair of antennas is used for touching (2). The next three pairs of limbs function as the jaw [mandible (3), 1st maxilla (4) and 2nd maxilla (5)]. Three pairs of jaw feet form a transition from the jaws to the feet (6,7,8). The next pair of limbs are the scissors (9), which are used to grab food and as a weapon. Only the inner part of the scissors is movable. A stronger sphincter muscle in the lower part of the outer part - located on the outside - and a weaker opener muscle in the lower part of the outer part - located inside - are the antagonists necessary for movement. Four pairs of walking feet (10,11,12,13), the actual locomotion organs, follow. The abdomen has five pairs of webbed feet (anal feet) (14,15,16,17,18); in the male the first two are transformed into mating organs, in the female the first is stunted. The penultimate pair is converted into fins and forms the tail fan (19) with the 21st unpaired link (telson). The scissors and walking feet each consist of five links, the joints are only thinly armored: Arthropods.
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