Small but perfectly formed: Tiny water flea has 31,000 genes, more than any other animal

• Daphnia pulex is the first crustacean to have a blueprint made showing the sequence of chemicals that make up genetic code

It may be a simple form of pond life, but in terms of genetic complexity the humble water flea beats humans hands down.

Scientists have learned that the 1mm-long creature has more genes than another other animal known.

In total, around 31,000 genes are packed into its DNA. In comparison, humans have only around 23,000.

Daphnia pulex: The common water flea - just 1mm-long - has more genes than another other animal known

The common water flea - Daphnia pulex - is the first crustacean to have a blueprint made showing the sequence of chemicals that make up genetic code, or genome.

At first glance Daphnia seems ordinary enough, having a transparent body, jointed limbs, compound eyes and a simple nervous and circulatory system.

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But its genome is not only unusually large but full of surprises.

'More than a third of Daphnia's genes are undocumented in any other organism - in other words, they are completely new to science,' said Dr Don Gilbert, one of the researchers from Indiana University.

Its peculiar genetic make-up mirrors unusual behaviour that has long been studied by scientists.

The animal has unique ways of responding to stress, with some species producing exaggerated tail spines, neck teeth or protective helmets when threatened by predators.

31,000 genes are packed into the water flea's DNA. Its peculiar genetic make-up mirrors unusual behaviour that has long been studied by scientists

Daphnia can also adapt to wide ranges in acidity, toxins, oxygen concentrations, food quality and temperature.

The creatures are able to reproduce both sexually and asexually. They thrive in the absence of males by clonal reproduction, until harsh environmental conditions favour the benefits of sex.

A high rate of gene duplication is the main reason why Daphnia has so many genes, say the researchers writing in the journal Science.

'We estimate a rate that is three times greater than those of other invertebrates and 30 per cent greater than that of humans,' said genome project director Dr John Colbourne, also from Indiana University.

The scientists hope that sequencing the Daphnia genome will lead to a better understanding of how organisms respond to environmental changes.