The food itself is ground by the trophi jaws , located just behind the mouth in the pharynx throat. Trophi are found in almost all rotifers, and are characteristic organs of the phylum Rotifera.
The body of the rotifer is externally but not internally segmented. The body is telescopic, with a semi-flexible, extendible, transparent cuticle covering. It is the cuticle that suggests rotifers are close relatives of roundworms and arthropods. Within the body are the stomach and reproductive organs. Genomes of bdelloid rotifers are weird. There are two copies of each gene as you expect of a diploid, but they are very different.
This suggests that they originated as a hybrid between two species whose genes and genomes diverged 60 million years ago. Their homologous chromosomes have been differently rearranged so they can't pair at meiosis. The conclusion is that bdelloid rotifers have eschewed sex for 60 million years.
Some genes were typical of fungi or bacteria, and endowed the rotifer with handy new properties such as breaking down toxins or using new foodstuffs. This " horizontal transfer " between rotifers and other organisms is ancient and ongoing. Foreign DNA is spread all over the rotifer genome.
So how did it get there? It seems that dehydration makes holes in cell membranes that can suck up DNA. The rotifers' efficient mechanism for repairing double stranded DNA breaks in dehydrated animals is perfect for incorporating foreign DNA into the genome.
More extraordinary still is what happens to DNA from other rotifer individuals or species. It isn't incorporated just anywhere in the genome, but lines up with the appropriate DNA sequence and recombines.
This means that a new version of a particular gene may replace the old. Just like sex. Bacteria reproduce by fission to make clones of genetically identical cells. But they can take up DNA from another bacterial strain , swap it for the resident gene, and express a variant protein in the wild. DNA transformation is only one of several tricks that bacteria use to scavenge variant and novel genes.
Bacteria can also receive little packages of foreign bacterial genes by way of a virus. Some bacteria can exchange long DNA molecules — even the whole genome — through tube-like structures. This conjugation looks most like what we would consider sex. In throwing up a great variety of genotypes, sexual reproduction still seems to be the best bet in the long run — for vertebrates and invertebrates.
In its absence, organisms such as the tiny rotifers have had to find other ways to boost their gene pool. Far from falsifying the theory that genetic variation is essential for evolutionary success, rotifers brilliantly confirm it.
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