Tadpole shrimp - Triops cancriformis |
Tadpole shrimps are small crustaceans that were already alive 300
million years ago. They are living fossils that have outlived the trilobites,
dinosaurs and mammoths and millions of other species.
They live in ponds and pools, an unstable habitat because they often
dry up during parts of the year.
The tadpole shrimp found in the Maltese islands, which goes by the
scientific name of Triops cancriformis, has existed unchanged for the
past 200 million years or so. It is the oldest living species known.
Triops
cancriformis is found in Europe, the Middle East and Japan. In many parts of Europe
it has lost its habitat and has decreased considerably. In some areas it is
endangered and strictly protected. Only two populations are known in the UK.
The tadpole shrimps I have seen in the Maltese islands have been about
six centimetres in length although it is not unknown for members of this
species to grow up to eleven centimetres long.
In Malta it has become very rare mainly because of destruction of its
habitat. Many of the sites in which it used to be found have disappeared and it
has also disappeared from most of its old but still existing sites.
Like the frog which shares the pools in which it lives, the tadpole
shrimp has a very fast life cycle. It becomes a mature adult within two or
three weeks of hatching. This allows it to complete its life cycle before the
rain pools in which they live dry up.
The eggs are very resistant to drought and extreme temperatures and can
survive for many years in the dried mud or dust at the bottom of a pool waiting
for the right hatching conditions. They can even survive digestive juices and
can pass through the digestive system of a bird unharmed. It is probably the
ability of the eggs to survive under very difficult conditions that has enables
the various species of triops to survive for so many millions of years.
Tadpole shrimps feed on small invertebrates, microscopic particles and
plants. They absorb oxygen through their legs and can be seen moving their legs
rhythmically all the time to move the water around them. They usually swim with
their shield upwards but when oxygen is scarce they swim upside down with their
feet close to the surface of the water where there is usually more oxygen.
The name Triops is derived from two Greek words meaning three and eyes.
It got its name because these species have a pair of compound eyes and a third
eye known as the ‘naupliar eye’ in between.
This article was published in The Times of Malta on 3 April 2014.
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