Platyhelminthes is divided into two categories, the trematodes and which other group?

Platyhelminthes, commonly known as flatworms, are divided into two main categories: trematodes, which are flukes, and cestodes, which are tapeworms. This classification is based on their morphology, life cycles, and various biological characteristics.

Cestodes are characterized by their long, flat bodies and lack of a digestive system, as they absorb nutrients directly through their skin from the host's intestines. Trematodes and cestodes share several features, such as being hermaphroditic and having complex life cycles involving multiple hosts, which further categorizes them under the phylum Platyhelminthes.

Other groups mentioned, such as nematodes (roundworms), oligochaetes, and polychaetes (both of which are types of annelids), do not belong to the Platyhelminthes phylum. Nematodes are distinct due to their round body shape and different biological processes, while oligochaetes and polychaetes have segmented bodies typical of annelids and are classified in a separate phylum altogether. Thus, the only correct pairing within the Platyhelminthes phylum in this context is between trematodes and cest