Fasciola belongs to class Trematoda of phylum Platyhelminthes. Animals of phylum Platyhelminthes possess an incomplete alimentary canal with only one opening, as the separate anus is absent. Undigested food material is probably ejected through the mouth or diffused into excretory system, so the correct answer is 2.

Explanation:

1) Unio:
Anus is present in Unio, which is a type of freshwater bivalve mollusk commonly known as a mussel. The anus is an opening at the end of the digestive tract that serves as an exit for undigested waste materials. The presence of an anus allows for the elimination of waste products from the body.

2) Fasciola:
Anus is absent in Fasciola, which is a parasitic flatworm commonly known as a liver fluke. These organisms have a complex digestive system but lack a separate anus. Instead, the waste materials are eliminated through the same opening where the food is ingested, which is known as the oral sucker. Therefore, Fasciola does not have a distinct anus.

3) Periplaneta:
Anus is present in Periplaneta, which is a type of cockroach commonly known as a household pest. Like most insects, Periplaneta has a complete digestive system with a distinct anus. The anus allows for the removal of undigested waste materials from the hindgut, which is the final section of the digestive tract.

Summary:
- Anus is present in Unio and Periplaneta.
- Anus is absent in Fasciola.
- Unio is a freshwater bivalve mollusk with a complete digestive system.
- Fasciola is a parasitic flatworm that lacks a distinct anus.
- Periplaneta is a cockroach with a complete digestive system and a distinct anus.