This stage corresponds to the ciliated larval stage of the Trematoda.
Similar to them in appearance are the flukes (Trematoda), of which the best known of a large variety is that which infests sheep.
This is the hirudinean of which we have spoken above, which is allied transitionally to the Trematoda.
The tristomes are not strictly entozoa, yet their internal organisation conforms more to the Trematoda than to the Hirudinid.
On anatomical grounds the affinity of the Cestoda to the Trematoda has been insisted on by the majority of anatomists.
It develops during the encapsuled state into a cystic worm, equivalent to the sporocyst of Trematoda.
Trematoda Trem·a·to·da (trěm'ə-tō'də)
A class of flatworms of the phylum Platyhelminthes, including both external and internal parasites of animal hosts, that have a thick outer cuticle and one or more suckers or hooks for attaching to host tissue; the flukes.