Suckers: trematodes have two distinctive structures called suckers, one anterior and one ventral. The former (also known as oral) is used for feeding; whereas the latter is used for attachment to their definitive habitat (e.g., vasculature, lung, liver) within the host.
Other unique structures: the outer surface of the adult worm is covered with a tegument (similar to cestodes), which serves as an absorbing surface. The tegument is covered by membrane-bound microvilli facilitating nutrient acquisition.
Digestive tract: unlike cestodes, trematodes have a functional blind gut into which they ingest and digest tissues of the host. However, it’s very rudimentary (unlike nematodes). Since the gut has no exit, wastes are regurgitated into the host.
Neuromuscular system: several layers of muscle lie just below the tegument, allowing trematodes to move about freely within the host. A pair of dorsal ganglia gives rise to lateral peripheral nerves running the length of the body, and they innervate the muscle layers.
Reproduction: worms are able to reproduce in various ways:
- Self-fertilization: this is when the worm possesses both sets of reproductive organs (e.g., Fasciola hepatica).
- Cross-fertilization: this happens between two worms possessing both sets of reproductive organs (e.g., Paragonimus westermani).
- Fertilization: happens between worms of the opposite sex, as is the case among the schistosomes. Remember the schistosomes mate for life and remain in copula in the vasculature laying eggs.
Figure 3. Notice both male and female schistosomes in copula
