Tardigrades and Crayfish: Moulting Animals
According to the taxonomic classification, the group Ecdysozoa
includes all living organisms which moult their exoskeletons, such as arthropods (insects, arachnids, crabs) and some smaller animal phyla, such as the tardigrades. During the geological Paleozoic era, exoskeletons became thicker in order to adapt to the changing environment. Let’s take a look at two living beings that underwent
said adaptation: the tardigrades which are remarkable survivors, and the European crayfish which lives under the protection of its shell.
Tardigrades
Tardigrades, also known as waterbears or moss piglets are micro-animals of about
a half millimetre in length, typically living on mosses, but found in nearly all environments. They can survive extreme conditions that would be fatal for most life on Earth.
Antenna
Crustacea typically have
two pairs of antennae.
The small antennules are fork-like.
Tolerance
According to experiments, tardigrades are capable of withstanding temperatures between –272 and 151 °C, both in a vacuum and under extremely high pressure – up to several thousand times normal atmospheric pressure, which is several times the pressure of water in the deepest oceanic trench, the Mariana Trench. They can also survive radioactivity, and X-ray
and UV radiation up to 1,000 times the lethal dose for humans.
Under extreme conditions, tardigrades are capable of reversibly suspending their metabolism and going into
this state by losing nearly 99% of the water content of their bodies, which helps survival.
If they get back to an adequate environment, even years later, they rehydrate and revert
to their normal state.
normal state
dehydrated state
Dehydrated state
Tardigrade
Geographical range: worldwide
Feeding behaviour: plant sap, decaying organic matter
Body length: 0.2–1.5 mm
European crayfish
Crayfish or crawfish are native to Central Europe and Southern Scandinavia. They are a protected species.They hunt at night – they
are predators that mostly eat insects, snails, tadpoles and small fish.
They may live for up to 20 years. Out of their five pairs of walking legs,
the first pair has turned into a pair of pincers. We can find further legs
on their abdomen as well. They have two cylinder-shaped, movable eyes.
Compound eye
It consists of thousands
of individual photoreceptor units. It provides advanced visual perception.
Exoskeleton
An external frame providing physical protection for the body. The exoskeleton of crustacea is hard, due to its calcium
carbonate content.
Walking legs
Carapace
In crustacea, the cephalon and
thorax – similarly to Arachnids –
are fused together.
European crayfish
Geographical range: Central Europe and Southern Scandinavia
Feeding behaviour: predator
Body length: male 20–25 cm, female smaller than 15 cm
Invertebrates
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Invertebrates
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