Flukes

A subclass of ectoparasitic flatworms usually found on freshwater fish, more rarely on amphibians or crustaceans. Body shape is variable but usually is much flattened and leaf-like. The epithelium is not ciliated. There is some form of holdfast organ near the mouth, which is either at or near the anterior tip of the body, and a second holdfast organ or set of organs near the posterior end. The gut is sac-like or else forked into two long blind tubes with or without diverticulae.

The order Monopisthocotylea contains about 15 families not all of which are recorded from Australia. The anterior part of the body has one or more pre-oral and/or oral suckers, or else paired muscular adhesive discs. The posterior has a single, flattened, holdfast organ comprising a sucker or suckers plus anchors and/or hooks.

Order Polyopisthocotylea contains about 29 families, not all recorded from Australia. The anterior part of the body has holdfast organs comprising one or more pre-oral or oral suckers or paired muscular adhesive discs, always with a pair of suckers in the buccal cavity. The posterior has two or more flattened, well-developed holdfast organs each with a sucker or suckers plus anchors and/or hooks.

Trematoda are not taken further in this set of keys.