First thought to have been single-celled organism, now seen as animals

Myxozoans have one of the smallest reported animal genomes

Myxozoan is known to infect commercial stock fish, like trout and salmon

When a myxozoan infects a rainbow trout, it causes the fish to go crazy and prevents the fish from controlling its behaviour.

Up until now, these tiny pests were considered protists, which is in the same group as amoebas, paramecia and slime molds.

However, a strange discover has led scientists to reclassify them as animals alongside jellyfish, coral and sea anemones - and could change the definition of what an animal is.

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Up until now, these tiny pests were considered protists, which is in the same group as amoebas, paramecia and slime molds. A recent discovery of a polar capsules in the parasites, which resembles the tentacle of a jellyfish, has re-categorized them as cnidarians -- the category with jellyfish, coral and sea anemones

'This is a remarkable case of extreme degeneration of an animal body plan, said Paulyn Cartwright, associate professor of ecology and evolutionary biology at the University of Kansas and principal on the research project.

'First, we confirmed they're cnidarians'.

'Now we need to investigate how they got to be that way.'

A recent discovery of a polar capsules in the parasites, which resembles the tentacle of a jellyfish, has re-categorized them as cnidarians - the category with jellyfish, coral and sea anemones.

With the help of genome sequencing, scientists have proof jellyfish have evolved into a 'really weird' microscopic organism, made of only a few cells and lives inside other animal.

Myxozoa has held on to its characteristics of the jellyfish, its stinger, despite its radical phasedown of the modern jellyfish and genome over millions of years. These findings, although stuff of scientific fascination, could have a commercial effect

WHAT ARE MYXOZOANS? In addition to data indicating the parasite evolved with a stripped-down body of just a few cells, researchers also found that the myxozoan genome was drastically simplified. The Myxozoan are a group of aquatic environments. Over 1300 species have been described and many have a two-host lifecycle, involving a fish and an annelid worm or bryozoan. The average size of a myxosporean spore usually ranges from 10 μm to 20 μm whereas that of a malacosporean spore can be up to 2 mm. Myxozoans can live in both fresh and marine habitats. Early thought to be unicellular, they are in fact multicellular organisms, probably extremely reduced cnidarians. Despite their inclusion in Cnidaria, the World Register of Marine Species still classifies myxozoa as a separate phylum under Animalia. Advertisement

In addition to data indicating the parasite evolved with a stripped-down body of just a few cells, researchers also found that the myxozoan genome was drastically simplified.

'These were 20 to 40 times smaller than average jellyfish genomes,' Cartwright said.

'It's one of the smallest animal genomes ever reported.'

'It only has about 20 million base pairs, whereas the average cnidarian has over 300 million.'

'These are tiny little genomes by comparison.'

The study looked at the genomes and surveys of action for two types of myxozoans.'

Myxozoa has held on to its characteristics of the jellyfish, its stinger, despite its radical phasedown of the modern jellyfish and genome over millions of years.

'Because they're so weird, it's difficult to imagine they were jellyfish,' said Cartwright.

'They don't have a mouth or a gut.'

'They have just a few cells'.

'But then they have this complex structure that looks just like stinging cell of cnidarian'.

These findings, although stuff of scientific fascination, could have a commercial effect.

Myxozoa is known to infect commercial stock fish, such as trout and salmon.

In addition to data indicating the parasite evolved with a stripped-down body of just a few cells, researchers also found that the myxozoan genome was drastically simplified. Features is a pictured of a Turritopsis nutricula jellyfish

'They're a very diverse group of parasites, and some have been well-studied because they infect fish and can wreak havoc in aquaculture of economic importance,' Cartwright said.

'They cause a whirling disease in salmon.'

'The fish start swimming in circles – it's a neurological problem caused by a myxozoan.'

These micro jellyfish are such a find, that it could expand the understanding of what makes up an animal.

Myxozoan's makeup was known to scientists, but there was gaps into where they evolved from, as noted by Cartwright.