Crayfish or crawfish (Astacus astacus) are native to Central Europe and Southern Scandinavia.
Adult males measure 20-25 cm (8-10 in), females are smaller than 15 cm (6 in). They prefer clean rivers and streams of plains. They are protected in some countries, as they used to be popular as food, they are quite rare these days.
They hunt at night – they are predators eating mostly insects, snails, tadpoles and small fish. They may live for up to 20years. Females shed their shell twice a year, while males molt only once a year. They are soft and unprotected after molting.
Out of their five pairs of walking legs, the first pair has turned into a pair of strong pincers. We can find further legs on their abdomen as well: males have 5+1 pairs, while females have 4+1 pairs of abdomen legs. They have two cylinder-shaped, movable eyes.
Females lay 60-150eggs in bunches onto their own abdomen legs between October and December, in a way that the eggs are fixed by a sticky excretion material, assuring the flow of water rich in oxygen through moving the legs. Out of the many eggs usually only 20small crabs grow up. After hatching, they stay on their mothers for two more weeks, and they only start their own life after this period.
- An external frame providing physical protection for the body. As it cannot grow with the body, it must be molted for the animal to grow. The exoskeleton of crustacea is hard, due to its calcium carbonate content.
- Crustaceans – similarly to other arthropods – have open circulatory systems. Hemolymph fills the heart, vessels and body cavities, and transports nutrients, metabolic wastes and respiratory gases.
- Crayfish have separate sexes and show sexual dimorphism. They reproduce by external fertilization. Females lay 200-300 eggs at a time and carry them on their abdomen legs.
- It in the brain and runs along the abdomen. The ganglia of the ventral nerve cord contain neuron cells and are joined by bundles of nerve fibers.