Mouthless and gutless animal????????

Paracatenula galateia, belong to the platyhelminths or flatworms, but inside they don't look like your usual fluke or tapeworm. Their bacteria-filled sac, called the trophosome, accounts for over 90% of the worm’s body and has cells called bacteriocytes that are filled with bacteria. In some species, the bacteria make up close to 50% of the total volume of the worm. By the way, the bacteria are quite big—5 to 8 μm in diameter. Incidentally, such large sizes are also seen in some insect bacterial endosymbionts.
For more information: http://www.ncbi.nlm.nih.gov/pubmed/22131640
http://schaechter.asmblog.org/