Questions: Monogenetic Trematodes Digenetic Trematodes

The answer is the first one: Monogenetic Trematodes.

Explanation:

• Monogenetic Trematodes are typically ectoparasites of fish, amphibians, and reptiles. They attach to the surfaces of gills, skin, the mouth, and fins, which aligns with the description provided in the question.
• Digenetic Trematodes, on the other hand, are usually endoparasites that have complex life cycles involving multiple hosts, including vertebrates and invertebrates, and are not typically found as ectoparasites on the surfaces of fish, amphibians, and reptiles.

Therefore, the correct answer is Monogenetic Trematodes.