PLATYHELMINTHES
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| An SEM and a diagram of a monogenean platyhelminth |
We briefly covered some of the main features of Monogenea, prominent fish ectoparasites, focusing on their external anatomy, which includes the presence of a complex structure at the posterior end, an opisthaptor, and an anterior adhesion organ, a prohaptor.
We then moved on to discuss the flukes, Trematoda. Some of their main characteristics are:
- They are all parasitic
- They use at least two hosts in their life cycle
- The intermediate host is usually a snail
- Final hosts are vertebrates
- Most of them are hermaphrodites
The stages that can enter a host are "equipped" with glands that produce enzymes that disrupt the host's tissues. One of the most interesting characteristics of trematodes is their capability to detect the correct host, and ignore individuals that cannot host them.
NEMERTEA - Ribbon worms
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| Nemerteans in natural habitat and with the proboscis everted |
The nemerteans, or "ribbon worms", are a phylum of unsegmented, dorsoventrally flat, mostly marine, organisms, that have a muscular, evertible proboscis independent from the digestive system. In some cases there is only one opening shared by the mouth and the proboscis, but still the cavity containing the proboscis, the rhynchocoel, is separate from the digestive tract.
We discussed locomotion, and the nervous, excretory, digestive and circulatory systems.
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