One example of animals having a single opening to the outside that serves both as mouth as well as anus is
- Octopus
- Asterias
- Ascidia
- Fasciola
Answer
(4) Fasciola
Solution
As per NCERT, animals with an incomplete digestive system have only a single opening to the outside which serves as both mouth and anus, e.g., Platyhelminthes.
∵ Fasciola (liver fluke) is a flatworm, whereas Octopus, Asterias and Ascidia have a complete digestive system with separate mouth and anus,
∴ the required example is Fasciola.
Answer: (4)