Phylum Platyhelminthes

Planaria, a flatworm, has a very high capacity for regeneration: a cut piece can grow into a complete animal.

A digestive system with only a single opening to the outside, which serves as both mouth and anus, is called an incomplete digestive system (blind-sac plan).
It is found in coelenterates and in platyhelminthes.
$Fasciola$ (liver fluke) is a flatworm of phylum Platyhelminthes, so it has an incomplete alimentary canal with a single opening.
$Octopus$ (Mollusca), $Asterias$ (Echinodermata) and $Ascidia$ (Urochordata) have a complete digestive system with separate mouth and anus.
Hence the example is $Fasciola$.